xnu-1228.9.59.tar.gz

[apple/xnu.git] / osfmk / vm / vm_fault.c

/*
 * Copyright (c) 2000-2007 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */
/* 
 * Mach Operating System
 * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University
 * All Rights Reserved.
 * 
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 * 
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 * 
 * Carnegie Mellon requests users of this software to return to
 * 
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 * 
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 */
/*
 *      File:   vm_fault.c
 *      Author: Avadis Tevanian, Jr., Michael Wayne Young
 *
 *      Page fault handling module.
 */

#include <mach_cluster_stats.h>
#include <mach_pagemap.h>
#include <mach_kdb.h>
#include <libkern/OSAtomic.h>

#include <mach/mach_types.h>
#include <mach/kern_return.h>
#include <mach/message.h>       /* for error codes */
#include <mach/vm_param.h>
#include <mach/vm_behavior.h>
#include <mach/memory_object.h>
                                /* For memory_object_data_{request,unlock} */
#include <mach/sdt.h>

#include <kern/kern_types.h>
#include <kern/host_statistics.h>
#include <kern/counters.h>
#include <kern/task.h>
#include <kern/thread.h>
#include <kern/sched_prim.h>
#include <kern/host.h>
#include <kern/xpr.h>
#include <kern/mach_param.h>
#include <kern/macro_help.h>
#include <kern/zalloc.h>
#include <kern/misc_protos.h>

#include <ppc/proc_reg.h>

#include <vm/vm_fault.h>
#include <vm/vm_map.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_kern.h>
#include <vm/pmap.h>
#include <vm/vm_pageout.h>
#include <vm/vm_protos.h>
#include <vm/vm_external.h>
#include <vm/memory_object.h>
#include <vm/vm_purgeable_internal.h>   /* Needed by some vm_page.h macros */

#include <sys/kdebug.h>

#define VM_FAULT_CLASSIFY       0

/* Zero-filled pages are marked "m->zero_fill" and put on the
 * special zero-fill inactive queue  only if they belong to
 * an object at least this big.
 */
#define VM_ZF_OBJECT_SIZE_THRESHOLD     (0x200000)

#define TRACEFAULTPAGE 0 /* (TEST/DEBUG) */

int     vm_object_pagein_throttle = 16;

extern int cs_debug;

#if     MACH_KDB
extern struct db_watchpoint *db_watchpoint_list;
#endif  /* MACH_KDB */


/* Forward declarations of internal routines. */
extern kern_return_t vm_fault_wire_fast(
                                vm_map_t        map,
                                vm_map_offset_t va,
                                vm_map_entry_t  entry,
                                pmap_t          pmap,
                                vm_map_offset_t pmap_addr);

extern void vm_fault_continue(void);

extern void vm_fault_copy_cleanup(
                                vm_page_t       page,
                                vm_page_t       top_page);

extern void vm_fault_copy_dst_cleanup(
                                vm_page_t       page);

#if     VM_FAULT_CLASSIFY
extern void vm_fault_classify(vm_object_t       object,
                          vm_object_offset_t    offset,
                          vm_prot_t             fault_type);

extern void vm_fault_classify_init(void);
#endif


unsigned long vm_cs_validates = 0;
unsigned long vm_cs_revalidates = 0;
unsigned long vm_cs_query_modified = 0;
unsigned long vm_cs_validated_dirtied = 0;

#if CONFIG_ENFORCE_SIGNED_CODE
#if SECURE_KERNEL
const int cs_enforcement_disable=0;
#else
int cs_enforcement_disable=1;
#endif
#endif

/*
 *      Routine:        vm_fault_init
 *      Purpose:
 *              Initialize our private data structures.
 */
void
vm_fault_init(void)
{
#if !SECURE_KERNEL
#if CONFIG_ENFORCE_SIGNED_CODE
        PE_parse_boot_argn("cs_enforcement_disable", &cs_enforcement_disable, sizeof (cs_enforcement_disable));
#endif
        PE_parse_boot_argn("cs_debug", &cs_debug, sizeof (cs_debug));
#endif
}

/*
 *      Routine:        vm_fault_cleanup
 *      Purpose:
 *              Clean up the result of vm_fault_page.
 *      Results:
 *              The paging reference for "object" is released.
 *              "object" is unlocked.
 *              If "top_page" is not null,  "top_page" is
 *              freed and the paging reference for the object
 *              containing it is released.
 *
 *      In/out conditions:
 *              "object" must be locked.
 */
void
vm_fault_cleanup(
        register vm_object_t    object,
        register vm_page_t      top_page)
{
        vm_object_paging_end(object);
        vm_object_unlock(object);

        if (top_page != VM_PAGE_NULL) {
                object = top_page->object;

                vm_object_lock(object);
                VM_PAGE_FREE(top_page);
                vm_object_paging_end(object);
                vm_object_unlock(object);
        }
}

#if     MACH_CLUSTER_STATS
#define MAXCLUSTERPAGES 16
struct {
        unsigned long pages_in_cluster;
        unsigned long pages_at_higher_offsets;
        unsigned long pages_at_lower_offsets;
} cluster_stats_in[MAXCLUSTERPAGES];
#define CLUSTER_STAT(clause)    clause
#define CLUSTER_STAT_HIGHER(x)  \
        ((cluster_stats_in[(x)].pages_at_higher_offsets)++)
#define CLUSTER_STAT_LOWER(x)   \
         ((cluster_stats_in[(x)].pages_at_lower_offsets)++)
#define CLUSTER_STAT_CLUSTER(x) \
        ((cluster_stats_in[(x)].pages_in_cluster)++)
#else   /* MACH_CLUSTER_STATS */
#define CLUSTER_STAT(clause)
#endif  /* MACH_CLUSTER_STATS */

#define ALIGNED(x) (((x) & (PAGE_SIZE_64 - 1)) == 0)


boolean_t       vm_page_deactivate_behind = TRUE;
/* 
 * default sizes given VM_BEHAVIOR_DEFAULT reference behavior 
 */
int vm_default_ahead = 0;
int vm_default_behind = MAX_UPL_TRANSFER;

#define MAX_SEQUENTIAL_RUN      (1024 * 1024 * 1024)

/*
 * vm_page_is_sequential
 *
 * Determine if sequential access is in progress
 * in accordance with the behavior specified.
 * Update state to indicate current access pattern.
 *
 * object must have at least the shared lock held
 */
static
void
vm_fault_is_sequential(
        vm_object_t             object,
        vm_object_offset_t      offset,
        vm_behavior_t           behavior)
{
        vm_object_offset_t      last_alloc;
        int                     sequential;
        int                     orig_sequential;

        last_alloc = object->last_alloc;
        sequential = object->sequential;
        orig_sequential = sequential;

        switch (behavior) {
        case VM_BEHAVIOR_RANDOM:
                /*
                 * reset indicator of sequential behavior
                 */
                sequential = 0;
                break;

        case VM_BEHAVIOR_SEQUENTIAL:
                if (offset && last_alloc == offset - PAGE_SIZE_64) {
                        /*
                         * advance indicator of sequential behavior
                         */
                        if (sequential < MAX_SEQUENTIAL_RUN)
                                sequential += PAGE_SIZE;
                } else {
                        /*
                         * reset indicator of sequential behavior
                         */
                        sequential = 0;
                }
                break;

        case VM_BEHAVIOR_RSEQNTL:
                if (last_alloc && last_alloc == offset + PAGE_SIZE_64) {
                        /*
                         * advance indicator of sequential behavior
                         */
                        if (sequential > -MAX_SEQUENTIAL_RUN)
                                sequential -= PAGE_SIZE;
                } else {
                        /*
                         * reset indicator of sequential behavior
                         */
                        sequential = 0;
                }
                break;

        case VM_BEHAVIOR_DEFAULT:
        default:
                if (offset && last_alloc == (offset - PAGE_SIZE_64)) {
                        /*
                         * advance indicator of sequential behavior
                         */
                        if (sequential < 0)
                                sequential = 0;
                        if (sequential < MAX_SEQUENTIAL_RUN)
                                sequential += PAGE_SIZE;

                } else if (last_alloc && last_alloc == (offset + PAGE_SIZE_64)) {
                        /*
                         * advance indicator of sequential behavior
                         */
                        if (sequential > 0)
                                sequential = 0;
                        if (sequential > -MAX_SEQUENTIAL_RUN)
                                sequential -= PAGE_SIZE;
                } else {
                        /*
                         * reset indicator of sequential behavior
                         */
                        sequential = 0;
                }
                break;
        }
        if (sequential != orig_sequential) {
                if (!OSCompareAndSwap(orig_sequential, sequential, (UInt32 *)&object->sequential)) {
                        /*
                         * if someone else has already updated object->sequential
                         * don't bother trying to update it or object->last_alloc
                         */
                        return;
                }
        }
        /*
         * I'd like to do this with a OSCompareAndSwap64, but that
         * doesn't exist for PPC...  however, it shouldn't matter
         * that much... last_alloc is maintained so that we can determine
         * if a sequential access pattern is taking place... if only
         * one thread is banging on this object, no problem with the unprotected
         * update... if 2 or more threads are banging away, we run the risk of
         * someone seeing a mangled update... however, in the face of multiple
         * accesses, no sequential access pattern can develop anyway, so we
         * haven't lost any real info.
         */
        object->last_alloc = offset;
}


/*
 * vm_page_deactivate_behind
 *
 * Determine if sequential access is in progress
 * in accordance with the behavior specified.  If
 * so, compute a potential page to deactivate and
 * deactivate it.
 *
 * object must be locked.
 *
 * return TRUE if we actually deactivate a page
 */
static
boolean_t
vm_fault_deactivate_behind(
        vm_object_t             object,
        vm_object_offset_t      offset,
        vm_behavior_t           behavior)
{
        vm_page_t       m = NULL;
        int             sequential_run;
        int             sequential_behavior = VM_BEHAVIOR_SEQUENTIAL;

#if TRACEFAULTPAGE
        dbgTrace(0xBEEF0018, (unsigned int) object, (unsigned int) vm_fault_deactivate_behind); /* (TEST/DEBUG) */
#endif

        if (object == kernel_object || vm_page_deactivate_behind == FALSE) {
                /*
                 * Do not deactivate pages from the kernel object: they
                 * are not intended to become pageable.
                 * or we've disabled the deactivate behind mechanism
                 */
                return FALSE;
        }
        if ((sequential_run = object->sequential)) {
                  if (sequential_run < 0) {
                          sequential_behavior = VM_BEHAVIOR_RSEQNTL;
                          sequential_run = 0 - sequential_run;
                  } else {
                          sequential_behavior = VM_BEHAVIOR_SEQUENTIAL;
                  }
        }
        switch (behavior) {
        case VM_BEHAVIOR_RANDOM:
                break;
        case VM_BEHAVIOR_SEQUENTIAL:
                if (sequential_run >= (int)PAGE_SIZE)
                        m = vm_page_lookup(object, offset - PAGE_SIZE_64);
                break;
        case VM_BEHAVIOR_RSEQNTL:
                if (sequential_run >= (int)PAGE_SIZE)
                        m = vm_page_lookup(object, offset + PAGE_SIZE_64);
                break;
        case VM_BEHAVIOR_DEFAULT:
        default:
        {       vm_object_offset_t behind = vm_default_behind * PAGE_SIZE_64;

                /*
                 * determine if the run of sequential accesss has been
                 * long enough on an object with default access behavior
                 * to consider it for deactivation
                 */
                if ((uint64_t)sequential_run >= behind) {
                        if (sequential_behavior == VM_BEHAVIOR_SEQUENTIAL) {
                                if (offset >= behind)
                                        m = vm_page_lookup(object, offset - behind);
                        } else {
                                if (offset < -behind)
                                        m = vm_page_lookup(object, offset + behind);
                        }
                }
                break;
        }
        }
        if (m) {
                if (!m->busy && !m->no_cache && !m->throttled && !m->fictitious && !m->absent) {
                        pmap_clear_reference(m->phys_page);
                        m->deactivated = TRUE;
#if TRACEFAULTPAGE
                        dbgTrace(0xBEEF0019, (unsigned int) object, (unsigned int) m);  /* (TEST/DEBUG) */
#endif
                        return TRUE;
                }
        }
        return FALSE;
}


/*
 * check for various conditions that would
 * prevent us from creating a ZF page...
 * cleanup is based on being called from vm_fault_page
 *
 * object must be locked
 * object == m->object
 */
static vm_fault_return_t
vm_fault_check(vm_object_t object, vm_page_t m, vm_page_t first_m, boolean_t interruptible_state)
{
        if (object->shadow_severed) {
                /*
                 * the shadow chain was severed
                 * just have to return an error at this point
                 */
                if (m != VM_PAGE_NULL)
                        VM_PAGE_FREE(m);
                vm_fault_cleanup(object, first_m);

                thread_interrupt_level(interruptible_state);

                return (VM_FAULT_MEMORY_ERROR);
        }
        if (vm_backing_store_low) {
                /*
                 * are we protecting the system from
                 * backing store exhaustion.  If so
                 * sleep unless we are privileged.
                 */
                if (!(current_task()->priv_flags & VM_BACKING_STORE_PRIV)) {

                        if (m != VM_PAGE_NULL)
                                VM_PAGE_FREE(m);
                        vm_fault_cleanup(object, first_m);

                        assert_wait((event_t)&vm_backing_store_low, THREAD_UNINT);

                        thread_block(THREAD_CONTINUE_NULL);
                        thread_interrupt_level(interruptible_state);

                        return (VM_FAULT_RETRY);
                }
        }
        if (VM_PAGE_ZFILL_THROTTLED()) {
                /*
                 * we're throttling zero-fills...
                 * treat this as if we couldn't grab a page
                 */
                if (m != VM_PAGE_NULL)
                        VM_PAGE_FREE(m);
                vm_fault_cleanup(object, first_m);

                thread_interrupt_level(interruptible_state);

                return (VM_FAULT_MEMORY_SHORTAGE);
        }
        return (VM_FAULT_SUCCESS);
}


/*
 * do the work to zero fill a page and
 * inject it into the correct paging queue
 *
 * m->object must be locked
 * page queue lock must NOT be held
 */
static int
vm_fault_zero_page(vm_page_t m, boolean_t no_zero_fill)
{
        int my_fault = DBG_ZERO_FILL_FAULT;

        /*
         * This is is a zero-fill page fault...
         *
         * Checking the page lock is a waste of
         * time;  this page was absent, so
         * it can't be page locked by a pager.
         *
         * we also consider it undefined
         * with respect to instruction
         * execution.  i.e. it is the responsibility
         * of higher layers to call for an instruction
         * sync after changing the contents and before
         * sending a program into this area.  We 
         * choose this approach for performance
         */
        m->pmapped = TRUE;

        m->cs_validated = FALSE;
        m->cs_tainted = FALSE;

        if (no_zero_fill == TRUE)
                my_fault = DBG_NZF_PAGE_FAULT;
        else {
                vm_page_zero_fill(m);

                VM_STAT_INCR(zero_fill_count);
                DTRACE_VM2(zfod, int, 1, (uint64_t *), NULL);
        }
        assert(!m->laundry);
        assert(m->object != kernel_object);
        //assert(m->pageq.next == NULL && m->pageq.prev == NULL);

        if (!IP_VALID(memory_manager_default) &&
                (m->object->purgable == VM_PURGABLE_DENY ||
                 m->object->purgable == VM_PURGABLE_NONVOLATILE ||
                 m->object->purgable == VM_PURGABLE_VOLATILE )) {
                vm_page_lock_queues();

                queue_enter(&vm_page_queue_throttled, m, vm_page_t, pageq);
                m->throttled = TRUE;
                vm_page_throttled_count++;

                vm_page_unlock_queues();
        } else {
                if (m->object->size > VM_ZF_OBJECT_SIZE_THRESHOLD) {
                        m->zero_fill = TRUE;
                        OSAddAtomic(1, (SInt32 *)&vm_zf_count);
                }
        }
        return (my_fault);
}


/*
 *      Routine:        vm_fault_page
 *      Purpose:
 *              Find the resident page for the virtual memory
 *              specified by the given virtual memory object
 *              and offset.
 *      Additional arguments:
 *              The required permissions for the page is given
 *              in "fault_type".  Desired permissions are included
 *              in "protection".
 *              fault_info is passed along to determine pagein cluster 
 *              limits... it contains the expected reference pattern,
 *              cluster size if available, etc...
 *
 *              If the desired page is known to be resident (for
 *              example, because it was previously wired down), asserting
 *              the "unwiring" parameter will speed the search.
 *
 *              If the operation can be interrupted (by thread_abort
 *              or thread_terminate), then the "interruptible"
 *              parameter should be asserted.
 *
 *      Results:
 *              The page containing the proper data is returned
 *              in "result_page".
 *
 *      In/out conditions:
 *              The source object must be locked and referenced,
 *              and must donate one paging reference.  The reference
 *              is not affected.  The paging reference and lock are
 *              consumed.
 *
 *              If the call succeeds, the object in which "result_page"
 *              resides is left locked and holding a paging reference.
 *              If this is not the original object, a busy page in the
 *              original object is returned in "top_page", to prevent other
 *              callers from pursuing this same data, along with a paging
 *              reference for the original object.  The "top_page" should
 *              be destroyed when this guarantee is no longer required.
 *              The "result_page" is also left busy.  It is not removed
 *              from the pageout queues.
 */

vm_fault_return_t
vm_fault_page(
        /* Arguments: */
        vm_object_t     first_object,   /* Object to begin search */
        vm_object_offset_t first_offset,        /* Offset into object */
        vm_prot_t       fault_type,     /* What access is requested */
        boolean_t       must_be_resident,/* Must page be resident? */
        /* Modifies in place: */
        vm_prot_t       *protection,    /* Protection for mapping */
        /* Returns: */
        vm_page_t       *result_page,   /* Page found, if successful */
        vm_page_t       *top_page,      /* Page in top object, if
                                         * not result_page.  */
        int             *type_of_fault, /* if non-null, fill in with type of fault
                                         * COW, zero-fill, etc... returned in trace point */
        /* More arguments: */
        kern_return_t   *error_code,    /* code if page is in error */
        boolean_t       no_zero_fill,   /* don't zero fill absent pages */
#if MACH_PAGEMAP
        boolean_t       data_supply,    /* treat as data_supply if 
                                         * it is a write fault and a full
                                         * page is provided */
#else
        __unused boolean_t data_supply,
#endif
        vm_object_fault_info_t fault_info)
{
        vm_page_t               m;
        vm_object_t             object;
        vm_object_offset_t      offset;
        vm_page_t               first_m;
        vm_object_t             next_object;
        vm_object_t             copy_object;
        boolean_t               look_for_page;
        vm_prot_t               access_required = fault_type;
        vm_prot_t               wants_copy_flag;
        CLUSTER_STAT(int pages_at_higher_offsets;)
        CLUSTER_STAT(int pages_at_lower_offsets;)
        kern_return_t           wait_result;
        boolean_t               interruptible_state;
        vm_fault_return_t       error;
        int                     my_fault;
        uint32_t                try_failed_count;
        int                     interruptible; /* how may fault be interrupted? */
        memory_object_t         pager;

/*
 * MACH page map - an optional optimization where a bit map is maintained
 * by the VM subsystem for internal objects to indicate which pages of
 * the object currently reside on backing store.  This existence map
 * duplicates information maintained by the vnode pager.  It is 
 * created at the time of the first pageout against the object, i.e. 
 * at the same time pager for the object is created.  The optimization
 * is designed to eliminate pager interaction overhead, if it is 
 * 'known' that the page does not exist on backing store.
 *
 * MUST_ASK_PAGER() evaluates to TRUE if the page specified by object/offset is 
 * either marked as paged out in the existence map for the object or no 
 * existence map exists for the object.  MUST_ASK_PAGER() is one of the
 * criteria in the decision to invoke the pager.   It is also used as one
 * of the criteria to terminate the scan for adjacent pages in a clustered
 * pagein operation.  Note that MUST_ASK_PAGER() always evaluates to TRUE for
 * permanent objects.  Note also that if the pager for an internal object 
 * has not been created, the pager is not invoked regardless of the value 
 * of MUST_ASK_PAGER() and that clustered pagein scans are only done on an object
 * for which a pager has been created.
 *
 * PAGED_OUT() evaluates to TRUE if the page specified by the object/offset
 * is marked as paged out in the existence map for the object.  PAGED_OUT()
 * PAGED_OUT() is used to determine if a page has already been pushed
 * into a copy object in order to avoid a redundant page out operation.
 */
#if MACH_PAGEMAP
#define MUST_ASK_PAGER(o, f) (vm_external_state_get((o)->existence_map, (f)) \
                        != VM_EXTERNAL_STATE_ABSENT)
#define PAGED_OUT(o, f) (vm_external_state_get((o)->existence_map, (f)) \
                        == VM_EXTERNAL_STATE_EXISTS)
#else
#define MUST_ASK_PAGER(o, f) (TRUE)
#define PAGED_OUT(o, f) (FALSE)
#endif

/*
 *      Recovery actions
 */
#define PREPARE_RELEASE_PAGE(m)                         \
        MACRO_BEGIN                                     \
        vm_page_lock_queues();                          \
        MACRO_END

#define DO_RELEASE_PAGE(m)                              \
        MACRO_BEGIN                                     \
        PAGE_WAKEUP_DONE(m);                            \
        if (!m->active && !m->inactive && !m->throttled)\
                vm_page_activate(m);                    \
        vm_page_unlock_queues();                        \
        MACRO_END

#define RELEASE_PAGE(m)                                 \
        MACRO_BEGIN                                     \
        PREPARE_RELEASE_PAGE(m);                        \
        DO_RELEASE_PAGE(m);                             \
        MACRO_END

#if TRACEFAULTPAGE
        dbgTrace(0xBEEF0002, (unsigned int) first_object, (unsigned int) first_offset); /* (TEST/DEBUG) */
#endif


#if     MACH_KDB
                /*
                 *      If there are watchpoints set, then
                 *      we don't want to give away write permission
                 *      on a read fault.  Make the task write fault,
                 *      so that the watchpoint code notices the access.
                 */
            if (db_watchpoint_list) {
                /*
                 *      If we aren't asking for write permission,
                 *      then don't give it away.  We're using write
                 *      faults to set the dirty bit.
                 */
                if (!(fault_type & VM_PROT_WRITE))
                        *protection &= ~VM_PROT_WRITE;
        }
#endif  /* MACH_KDB */

        interruptible = fault_info->interruptible;
        interruptible_state = thread_interrupt_level(interruptible);
 
        /*
         *      INVARIANTS (through entire routine):
         *
         *      1)      At all times, we must either have the object
         *              lock or a busy page in some object to prevent
         *              some other thread from trying to bring in
         *              the same page.
         *
         *              Note that we cannot hold any locks during the
         *              pager access or when waiting for memory, so
         *              we use a busy page then.
         *
         *      2)      To prevent another thread from racing us down the
         *              shadow chain and entering a new page in the top
         *              object before we do, we must keep a busy page in
         *              the top object while following the shadow chain.
         *
         *      3)      We must increment paging_in_progress on any object
         *              for which we have a busy page before dropping
         *              the object lock
         *
         *      4)      We leave busy pages on the pageout queues.
         *              If the pageout daemon comes across a busy page,
         *              it will remove the page from the pageout queues.
         */

        object = first_object;
        offset = first_offset;
        first_m = VM_PAGE_NULL;
        access_required = fault_type;


        XPR(XPR_VM_FAULT,
                "vm_f_page: obj 0x%X, offset 0x%X, type %d, prot %d\n",
                (integer_t)object, offset, fault_type, *protection, 0);

        /*
         * default type of fault
         */
        my_fault = DBG_CACHE_HIT_FAULT;

        while (TRUE) {
#if TRACEFAULTPAGE
                dbgTrace(0xBEEF0003, (unsigned int) 0, (unsigned int) 0);       /* (TEST/DEBUG) */
#endif
                if (!object->alive) {
                        /*
                         * object is no longer valid
                         * clean up and return error
                         */
                        vm_fault_cleanup(object, first_m);
                        thread_interrupt_level(interruptible_state);

                        return (VM_FAULT_MEMORY_ERROR);
                }

                /*
                 * See whether the page at 'offset' is resident
                 */
                m = vm_page_lookup(object, offset);
#if TRACEFAULTPAGE
                dbgTrace(0xBEEF0004, (unsigned int) m, (unsigned int) object);  /* (TEST/DEBUG) */
#endif
                if (m != VM_PAGE_NULL) {

                        if (m->busy) {
                                /*
                                 * The page is being brought in,
                                 * wait for it and then retry.
                                 *
                                 * A possible optimization: if the page
                                 * is known to be resident, we can ignore
                                 * pages that are absent (regardless of
                                 * whether they're busy).
                                 */
#if TRACEFAULTPAGE
                                dbgTrace(0xBEEF0005, (unsigned int) m, (unsigned int) 0);       /* (TEST/DEBUG) */
#endif
                                wait_result = PAGE_SLEEP(object, m, interruptible);
                                XPR(XPR_VM_FAULT,
                                    "vm_f_page: block busy obj 0x%X, offset 0x%X, page 0x%X\n",
                                        (integer_t)object, offset,
                                        (integer_t)m, 0, 0);
                                counter(c_vm_fault_page_block_busy_kernel++);

                                if (wait_result != THREAD_AWAKENED) {
                                        vm_fault_cleanup(object, first_m);
                                        thread_interrupt_level(interruptible_state);

                                        if (wait_result == THREAD_RESTART)
                                                return (VM_FAULT_RETRY);
                                        else
                                                return (VM_FAULT_INTERRUPTED);
                                }
                                continue;
                        }

                        if (m->phys_page == vm_page_guard_addr) {
                                /*
                                 * Guard page: off limits !
                                 */
                                if (fault_type == VM_PROT_NONE) {
                                        /*
                                         * The fault is not requesting any
                                         * access to the guard page, so it must
                                         * be just to wire or unwire it.
                                         * Let's pretend it succeeded...
                                         */
                                        m->busy = TRUE;
                                        *result_page = m;
                                        assert(first_m == VM_PAGE_NULL);
                                        *top_page = first_m;
                                        if (type_of_fault)
                                                *type_of_fault = DBG_GUARD_FAULT;
                                        return VM_FAULT_SUCCESS;
                                } else {
                                        /*
                                         * The fault requests access to the
                                         * guard page: let's deny that !
                                         */
                                        vm_fault_cleanup(object, first_m);
                                        thread_interrupt_level(interruptible_state);
                                        return VM_FAULT_MEMORY_ERROR;
                                }
                        }

                        if (m->error) {
                                /*
                                 * The page is in error, give up now.
                                 */
#if TRACEFAULTPAGE
                                dbgTrace(0xBEEF0006, (unsigned int) m, (unsigned int) error_code);      /* (TEST/DEBUG) */
#endif
                                if (error_code)
                                        *error_code = KERN_MEMORY_ERROR;
                                VM_PAGE_FREE(m);

                                vm_fault_cleanup(object, first_m);
                                thread_interrupt_level(interruptible_state);

                                return (VM_FAULT_MEMORY_ERROR);
                        }
                        if (m->restart) {
                                /*
                                 * The pager wants us to restart
                                 * at the top of the chain,
                                 * typically because it has moved the
                                 * page to another pager, then do so.
                                 */
#if TRACEFAULTPAGE
                                dbgTrace(0xBEEF0007, (unsigned int) m, (unsigned int) 0);       /* (TEST/DEBUG) */
#endif
                                VM_PAGE_FREE(m);

                                vm_fault_cleanup(object, first_m);
                                thread_interrupt_level(interruptible_state);

                                return (VM_FAULT_RETRY);
                        }
                        if (m->absent) {
                                /*
                                 * The page isn't busy, but is absent,
                                 * therefore it's deemed "unavailable".
                                 *
                                 * Remove the non-existent page (unless it's
                                 * in the top object) and move on down to the
                                 * next object (if there is one).
                                 */
#if TRACEFAULTPAGE
                                dbgTrace(0xBEEF0008, (unsigned int) m, (unsigned int) object->shadow);  /* (TEST/DEBUG) */
#endif
                                next_object = object->shadow;

                                if (next_object == VM_OBJECT_NULL) {
                                        /*
                                         * Absent page at bottom of shadow
                                         * chain; zero fill the page we left
                                         * busy in the first object, and free
                                         * the absent page.
                                         */
                                        assert(!must_be_resident);

                                        /*
                                         * check for any conditions that prevent
                                         * us from creating a new zero-fill page
                                         * vm_fault_check will do all of the 
                                         * fault cleanup in the case of an error condition
                                         * including resetting the thread_interrupt_level
                                         */
                                        error = vm_fault_check(object, m, first_m, interruptible_state);

                                        if (error != VM_FAULT_SUCCESS)
                                                return (error);

                                        XPR(XPR_VM_FAULT,
                                            "vm_f_page: zero obj 0x%X, off 0x%X, page 0x%X, first_obj 0x%X\n",
                                                (integer_t)object, offset,
                                                (integer_t)m,
                                                (integer_t)first_object, 0);

                                        if (object != first_object) {
                                                /*
                                                 * free the absent page we just found
                                                 */
                                                VM_PAGE_FREE(m);

                                                /*
                                                 * drop reference and lock on current object
                                                 */
                                                vm_object_paging_end(object);
                                                vm_object_unlock(object);

                                                /*
                                                 * grab the original page we 
                                                 * 'soldered' in place and
                                                 * retake lock on 'first_object'
                                                 */
                                                m = first_m;
                                                first_m = VM_PAGE_NULL;

                                                object = first_object;
                                                offset = first_offset;

                                                vm_object_lock(object);
                                        } else {
                                                /*
                                                 * we're going to use the absent page we just found
                                                 * so convert it to a 'busy' page
                                                 */
                                                m->absent = FALSE;
                                                m->busy = TRUE;
                                        }
                                        /*
                                         * zero-fill the page and put it on
                                         * the correct paging queue
                                         */
                                        my_fault = vm_fault_zero_page(m, no_zero_fill);

                                        break;
                                } else {
                                        if (must_be_resident)
                                                vm_object_paging_end(object);
                                        else if (object != first_object) {
                                                vm_object_paging_end(object);
                                                VM_PAGE_FREE(m);
                                        } else {
                                                first_m = m;
                                                m->absent = FALSE;
                                                m->busy = TRUE;

                                                vm_page_lockspin_queues();
                                                VM_PAGE_QUEUES_REMOVE(m);
                                                vm_page_unlock_queues();
                                        }
                                        XPR(XPR_VM_FAULT,
                                            "vm_f_page: unavail obj 0x%X, off 0x%X, next_obj 0x%X, newoff 0x%X\n",
                                                (integer_t)object, offset,
                                                (integer_t)next_object,
                                                offset+object->shadow_offset,0);

                                        offset += object->shadow_offset;
                                        fault_info->lo_offset += object->shadow_offset;
                                        fault_info->hi_offset += object->shadow_offset;
                                        access_required = VM_PROT_READ;

                                        vm_object_lock(next_object);
                                        vm_object_unlock(object);
                                        object = next_object;
                                        vm_object_paging_begin(object);
                                        
                                        /*
                                         * reset to default type of fault
                                         */
                                        my_fault = DBG_CACHE_HIT_FAULT;

                                        continue;
                                }
                        }
                        if ((m->cleaning)
                            && ((object != first_object) || (object->copy != VM_OBJECT_NULL))
                            && (fault_type & VM_PROT_WRITE)) {
                                /*
                                 * This is a copy-on-write fault that will
                                 * cause us to revoke access to this page, but
                                 * this page is in the process of being cleaned
                                 * in a clustered pageout. We must wait until
                                 * the cleaning operation completes before
                                 * revoking access to the original page,
                                 * otherwise we might attempt to remove a
                                 * wired mapping.
                                 */
#if TRACEFAULTPAGE
                                dbgTrace(0xBEEF0009, (unsigned int) m, (unsigned int) offset);  /* (TEST/DEBUG) */
#endif
                                XPR(XPR_VM_FAULT,
                                    "vm_f_page: cleaning obj 0x%X, offset 0x%X, page 0x%X\n",
                                        (integer_t)object, offset,
                                        (integer_t)m, 0, 0);
                                /*
                                 * take an extra ref so that object won't die
                                 */
                                vm_object_reference_locked(object);

                                vm_fault_cleanup(object, first_m);
                                
                                counter(c_vm_fault_page_block_backoff_kernel++);
                                vm_object_lock(object);
                                assert(object->ref_count > 0);

                                m = vm_page_lookup(object, offset);

                                if (m != VM_PAGE_NULL && m->cleaning) {
                                        PAGE_ASSERT_WAIT(m, interruptible);

                                        vm_object_unlock(object);
                                        wait_result = thread_block(THREAD_CONTINUE_NULL);
                                        vm_object_deallocate(object);

                                        goto backoff;
                                } else {
                                        vm_object_unlock(object);

                                        vm_object_deallocate(object);
                                        thread_interrupt_level(interruptible_state);

                                        return (VM_FAULT_RETRY);
                                }
                        }
                        if (type_of_fault == NULL && m->speculative) {
                                /*
                                 * If we were passed a non-NULL pointer for
                                 * "type_of_fault", than we came from
                                 * vm_fault... we'll let it deal with
                                 * this condition, since it
                                 * needs to see m->speculative to correctly
                                 * account the pageins, otherwise...
                                 * take it off the speculative queue, we'll
                                 * let the caller of vm_fault_page deal
                                 * with getting it onto the correct queue
                                 */
                                vm_page_lockspin_queues();
                                VM_PAGE_QUEUES_REMOVE(m);
                                vm_page_unlock_queues();
                        }

                        if (m->encrypted) {
                                /*
                                 * ENCRYPTED SWAP:
                                 * the user needs access to a page that we
                                 * encrypted before paging it out.
                                 * Decrypt the page now.
                                 * Keep it busy to prevent anyone from
                                 * accessing it during the decryption.
                                 */
                                m->busy = TRUE;
                                vm_page_decrypt(m, 0);
                                assert(object == m->object);
                                assert(m->busy);
                                PAGE_WAKEUP_DONE(m);

                                /*
                                 * Retry from the top, in case
                                 * something changed while we were
                                 * decrypting.
                                 */
                                continue;
                        }
                        ASSERT_PAGE_DECRYPTED(m);

                        if (m->object->code_signed) {
                                /*
                                 * CODE SIGNING:
                                 * We just paged in a page from a signed
                                 * memory object but we don't need to
                                 * validate it now.  We'll validate it if
                                 * when it gets mapped into a user address
                                 * space for the first time or when the page
                                 * gets copied to another object as a result
                                 * of a copy-on-write.
                                 */
                        }

                        /*
                         * We mark the page busy and leave it on
                         * the pageout queues.  If the pageout
                         * deamon comes across it, then it will
                         * remove the page from the queue, but not the object
                         */
#if TRACEFAULTPAGE
                        dbgTrace(0xBEEF000B, (unsigned int) m, (unsigned int) 0);       /* (TEST/DEBUG) */
#endif
                        XPR(XPR_VM_FAULT,
                            "vm_f_page: found page obj 0x%X, offset 0x%X, page 0x%X\n",
                                (integer_t)object, offset, (integer_t)m, 0, 0);
                        assert(!m->busy);
                        assert(!m->absent);

                        m->busy = TRUE;
                        break;
                }
                

                /*
                 * we get here when there is no page present in the object at
                 * the offset we're interested in... we'll allocate a page
                 * at this point if the pager associated with
                 * this object can provide the data or we're the top object...
                 * object is locked;  m == NULL
                 */
                look_for_page = (object->pager_created && (MUST_ASK_PAGER(object, offset) == TRUE) && !data_supply);
                
#if TRACEFAULTPAGE
                dbgTrace(0xBEEF000C, (unsigned int) look_for_page, (unsigned int) object);      /* (TEST/DEBUG) */
#endif
                if ((look_for_page || (object == first_object)) && !must_be_resident && !object->phys_contiguous) {
                        /*
                         * Allocate a new page for this object/offset pair
                         */
                        m = vm_page_grab();
#if TRACEFAULTPAGE
                        dbgTrace(0xBEEF000D, (unsigned int) m, (unsigned int) object);  /* (TEST/DEBUG) */
#endif
                        if (m == VM_PAGE_NULL) {

                                vm_fault_cleanup(object, first_m);
                                thread_interrupt_level(interruptible_state);

                                return (VM_FAULT_MEMORY_SHORTAGE);
                        }
                        vm_page_insert(m, object, offset);
                }
                if (look_for_page && !must_be_resident) {
                        kern_return_t   rc;

                        /*
                         *      If the memory manager is not ready, we
                         *      cannot make requests.
                         */
                        if (!object->pager_ready) {
#if TRACEFAULTPAGE
                                dbgTrace(0xBEEF000E, (unsigned int) 0, (unsigned int) 0);       /* (TEST/DEBUG) */
#endif
                                if (m != VM_PAGE_NULL)
                                        VM_PAGE_FREE(m);

                                XPR(XPR_VM_FAULT,
                                "vm_f_page: ready wait obj 0x%X, offset 0x%X\n",
                                        (integer_t)object, offset, 0, 0, 0);

                                /*
                                 * take an extra ref so object won't die
                                 */
                                vm_object_reference_locked(object);
                                vm_fault_cleanup(object, first_m);
                                counter(c_vm_fault_page_block_backoff_kernel++);

                                vm_object_lock(object);
                                assert(object->ref_count > 0);

                                if (!object->pager_ready) {
                                        wait_result = vm_object_assert_wait(object, VM_OBJECT_EVENT_PAGER_READY, interruptible);

                                        vm_object_unlock(object);
                                        if (wait_result == THREAD_WAITING)
                                                wait_result = thread_block(THREAD_CONTINUE_NULL);
                                        vm_object_deallocate(object);

                                        goto backoff;
                                } else {
                                        vm_object_unlock(object);
                                        vm_object_deallocate(object);
                                        thread_interrupt_level(interruptible_state);

                                        return (VM_FAULT_RETRY);
                                }
                        }
                        if (!object->internal && !object->phys_contiguous && object->paging_in_progress > vm_object_pagein_throttle) {
                                /*
                                 * If there are too many outstanding page
                                 * requests pending on this external object, we
                                 * wait for them to be resolved now.
                                 */
#if TRACEFAULTPAGE
                                dbgTrace(0xBEEF0010, (unsigned int) m, (unsigned int) 0);       /* (TEST/DEBUG) */
#endif
                                if (m != VM_PAGE_NULL)
                                        VM_PAGE_FREE(m);
                                /*
                                 * take an extra ref so object won't die
                                 */
                                vm_object_reference_locked(object);

                                vm_fault_cleanup(object, first_m);

                                counter(c_vm_fault_page_block_backoff_kernel++);

                                vm_object_lock(object);
                                assert(object->ref_count > 0);

                                if (object->paging_in_progress > vm_object_pagein_throttle) {
                                        vm_object_assert_wait(object, VM_OBJECT_EVENT_PAGING_IN_PROGRESS, interruptible);

                                        vm_object_unlock(object);
                                        wait_result = thread_block(THREAD_CONTINUE_NULL);
                                        vm_object_deallocate(object);

                                        goto backoff;
                                } else {
                                        vm_object_unlock(object);
                                        vm_object_deallocate(object);
                                        thread_interrupt_level(interruptible_state);

                                        return (VM_FAULT_RETRY);
                                }
                        }
                        if (m != VM_PAGE_NULL) {
                                /*
                                 * Indicate that the page is waiting for data
                                 * from the memory manager.
                                 */
                                m->list_req_pending = TRUE;
                                m->absent = TRUE;
                        }

#if TRACEFAULTPAGE
                        dbgTrace(0xBEEF0012, (unsigned int) object, (unsigned int) 0);  /* (TEST/DEBUG) */
#endif

                        /*
                         * It's possible someone called vm_object_destroy while we weren't
                         * holding the object lock.  If that has happened, then bail out 
                         * here.
                         */

                        pager = object->pager;

                        if (pager == MEMORY_OBJECT_NULL) {
                                vm_fault_cleanup(object, first_m);
                                thread_interrupt_level(interruptible_state);
                                return VM_FAULT_MEMORY_ERROR;
                        }

                        /*
                         * We have an absent page in place for the faulting offset,
                         * so we can release the object lock.
                         */

                        vm_object_unlock(object);

                        /*
                         * If this object uses a copy_call strategy,
                         * and we are interested in a copy of this object
                         * (having gotten here only by following a
                         * shadow chain), then tell the memory manager
                         * via a flag added to the desired_access
                         * parameter, so that it can detect a race
                         * between our walking down the shadow chain
                         * and its pushing pages up into a copy of
                         * the object that it manages.
                         */
                        if (object->copy_strategy == MEMORY_OBJECT_COPY_CALL && object != first_object)
                                wants_copy_flag = VM_PROT_WANTS_COPY;
                        else
                                wants_copy_flag = VM_PROT_NONE;

                        XPR(XPR_VM_FAULT,
                            "vm_f_page: data_req obj 0x%X, offset 0x%X, page 0x%X, acc %d\n",
                                (integer_t)object, offset, (integer_t)m,
                                access_required | wants_copy_flag, 0);

                        /*
                         * Call the memory manager to retrieve the data.
                         */
                        rc = memory_object_data_request(
                                pager,
                                offset + object->paging_offset,
                                PAGE_SIZE,
                                access_required | wants_copy_flag,
                                (memory_object_fault_info_t)fault_info);

#if TRACEFAULTPAGE
                        dbgTrace(0xBEEF0013, (unsigned int) object, (unsigned int) rc); /* (TEST/DEBUG) */
#endif
                        vm_object_lock(object);

                        if (rc != KERN_SUCCESS) {

                                vm_fault_cleanup(object, first_m);
                                thread_interrupt_level(interruptible_state);

                                return ((rc == MACH_SEND_INTERRUPTED) ?
                                        VM_FAULT_INTERRUPTED :
                                        VM_FAULT_MEMORY_ERROR);
                        }
                        if ((interruptible != THREAD_UNINT) && (current_thread()->sched_mode & TH_MODE_ABORT)) {

                                vm_fault_cleanup(object, first_m);
                                thread_interrupt_level(interruptible_state);

                                return (VM_FAULT_INTERRUPTED);
                        }
                        if (m == VM_PAGE_NULL && object->phys_contiguous) {
                                /*
                                 * No page here means that the object we
                                 * initially looked up was "physically 
                                 * contiguous" (i.e. device memory).  However,
                                 * with Virtual VRAM, the object might not
                                 * be backed by that device memory anymore,
                                 * so we're done here only if the object is
                                 * still "phys_contiguous".
                                 * Otherwise, if the object is no longer
                                 * "phys_contiguous", we need to retry the
                                 * page fault against the object's new backing
                                 * store (different memory object).
                                 */
                                break;
                        }
                        /*
                         * potentially a pagein fault
                         * if we make it through the state checks
                         * above, than we'll count it as such
                         */
                        my_fault = DBG_PAGEIN_FAULT;

                        /*
                         * Retry with same object/offset, since new data may
                         * be in a different page (i.e., m is meaningless at
                         * this point).
                         */
                        continue;
                }

                /*
                 * We get here if the object has no pager, or an existence map 
                 * exists and indicates the page isn't present on the pager
                 * or we're unwiring a page.  If a pager exists, but there
                 * is no existence map, then the m->absent case above handles
                 * the ZF case when the pager can't provide the page
                 */
#if TRACEFAULTPAGE
                dbgTrace(0xBEEF0014, (unsigned int) object, (unsigned int) m);  /* (TEST/DEBUG) */
#endif
                if (object == first_object)
                        first_m = m;
                else
                        assert(m == VM_PAGE_NULL);

                XPR(XPR_VM_FAULT,
                    "vm_f_page: no pager obj 0x%X, offset 0x%X, page 0x%X, next_obj 0x%X\n",
                        (integer_t)object, offset, (integer_t)m,
                        (integer_t)object->shadow, 0);

                next_object = object->shadow;

                if (next_object == VM_OBJECT_NULL) {
                        /*
                         * we've hit the bottom of the shadown chain,
                         * fill the page in the top object with zeros.
                         */
                        assert(!must_be_resident);

                        if (object != first_object) {
                                vm_object_paging_end(object);
                                vm_object_unlock(object);

                                object = first_object;
                                offset = first_offset;
                                vm_object_lock(object);
                        }
                        m = first_m;
                        assert(m->object == object);
                        first_m = VM_PAGE_NULL;

                        /*
                         * check for any conditions that prevent
                         * us from creating a new zero-fill page
                         * vm_fault_check will do all of the 
                         * fault cleanup in the case of an error condition
                         * including resetting the thread_interrupt_level
                         */
                        error = vm_fault_check(object, m, first_m, interruptible_state);

                        if (error != VM_FAULT_SUCCESS)
                                return (error);

                        if (m == VM_PAGE_NULL) {
                                m = vm_page_grab();

                                if (m == VM_PAGE_NULL) {
                                        vm_fault_cleanup(object, VM_PAGE_NULL);
                                        thread_interrupt_level(interruptible_state);

                                        return (VM_FAULT_MEMORY_SHORTAGE);
                                }
                                vm_page_insert(m, object, offset);
                        }
                        my_fault = vm_fault_zero_page(m, no_zero_fill);

                        break;

                } else {
                        /*
                         * Move on to the next object.  Lock the next
                         * object before unlocking the current one.
                         */
                        if ((object != first_object) || must_be_resident)
                                vm_object_paging_end(object);

                        offset += object->shadow_offset;
                        fault_info->lo_offset += object->shadow_offset;
                        fault_info->hi_offset += object->shadow_offset;
                        access_required = VM_PROT_READ;

                        vm_object_lock(next_object);
                        vm_object_unlock(object);

                        object = next_object;
                        vm_object_paging_begin(object);
                }
        }

        /*
         *      PAGE HAS BEEN FOUND.
         *
         *      This page (m) is:
         *              busy, so that we can play with it;
         *              not absent, so that nobody else will fill it;
         *              possibly eligible for pageout;
         *
         *      The top-level page (first_m) is:
         *              VM_PAGE_NULL if the page was found in the
         *               top-level object;
         *              busy, not absent, and ineligible for pageout.
         *
         *      The current object (object) is locked.  A paging
         *      reference is held for the current and top-level
         *      objects.
         */

#if TRACEFAULTPAGE
        dbgTrace(0xBEEF0015, (unsigned int) object, (unsigned int) m);  /* (TEST/DEBUG) */
#endif
#if     EXTRA_ASSERTIONS
        if (m != VM_PAGE_NULL) {
                assert(m->busy && !m->absent);
                assert((first_m == VM_PAGE_NULL) ||
                        (first_m->busy && !first_m->absent &&
                         !first_m->active && !first_m->inactive));
        }
#endif  /* EXTRA_ASSERTIONS */

        /*
         * ENCRYPTED SWAP:
         * If we found a page, we must have decrypted it before we
         * get here...
         */
        if (m != VM_PAGE_NULL) {
                ASSERT_PAGE_DECRYPTED(m);
        }

        XPR(XPR_VM_FAULT,
            "vm_f_page: FOUND obj 0x%X, off 0x%X, page 0x%X, 1_obj 0x%X, 1_m 0x%X\n",
                (integer_t)object, offset, (integer_t)m,
                (integer_t)first_object, (integer_t)first_m);

        /*
         * If the page is being written, but isn't
         * already owned by the top-level object,
         * we have to copy it into a new page owned
         * by the top-level object.
         */
        if ((object != first_object) && (m != VM_PAGE_NULL)) {

#if TRACEFAULTPAGE
                dbgTrace(0xBEEF0016, (unsigned int) object, (unsigned int) fault_type); /* (TEST/DEBUG) */
#endif
                if (fault_type & VM_PROT_WRITE) {
                        vm_page_t copy_m;

                        /*
                         * We only really need to copy if we
                         * want to write it.
                         */
                        assert(!must_be_resident);

                        /*
                         * are we protecting the system from
                         * backing store exhaustion.  If so
                         * sleep unless we are privileged.
                         */
                        if (vm_backing_store_low) {
                                if (!(current_task()->priv_flags & VM_BACKING_STORE_PRIV)) {

                                        RELEASE_PAGE(m);
                                        vm_fault_cleanup(object, first_m);

                                        assert_wait((event_t)&vm_backing_store_low, THREAD_UNINT);

                                        thread_block(THREAD_CONTINUE_NULL);
                                        thread_interrupt_level(interruptible_state);

                                        return (VM_FAULT_RETRY);
                                }
                        }
                        /*
                         * If we try to collapse first_object at this
                         * point, we may deadlock when we try to get
                         * the lock on an intermediate object (since we
                         * have the bottom object locked).  We can't
                         * unlock the bottom object, because the page
                         * we found may move (by collapse) if we do.
                         *
                         * Instead, we first copy the page.  Then, when
                         * we have no more use for the bottom object,
                         * we unlock it and try to collapse.
                         *
                         * Note that we copy the page even if we didn't
                         * need to... that's the breaks.
                         */

                        /*
                         * Allocate a page for the copy
                         */
                        copy_m = vm_page_grab();

                        if (copy_m == VM_PAGE_NULL) {
                                RELEASE_PAGE(m);

                                vm_fault_cleanup(object, first_m);
                                thread_interrupt_level(interruptible_state);

                                return (VM_FAULT_MEMORY_SHORTAGE);
                        }
                        XPR(XPR_VM_FAULT,
                            "vm_f_page: page_copy obj 0x%X, offset 0x%X, m 0x%X, copy_m 0x%X\n",
                                (integer_t)object, offset,
                                (integer_t)m, (integer_t)copy_m, 0);

                        vm_page_copy(m, copy_m);

                        /*
                         * If another map is truly sharing this
                         * page with us, we have to flush all
                         * uses of the original page, since we
                         * can't distinguish those which want the
                         * original from those which need the
                         * new copy.
                         *
                         * XXXO If we know that only one map has
                         * access to this page, then we could
                         * avoid the pmap_disconnect() call.
                         */
                        if (m->pmapped)
                                pmap_disconnect(m->phys_page);

                        assert(!m->cleaning);

                        /*
                         * We no longer need the old page or object.
                         */
                        PAGE_WAKEUP_DONE(m);
                        vm_object_paging_end(object);
                        vm_object_unlock(object);

                        my_fault = DBG_COW_FAULT;
                        VM_STAT_INCR(cow_faults);
                        DTRACE_VM2(cow_fault, int, 1, (uint64_t *), NULL);
                        current_task()->cow_faults++;

                        object = first_object;
                        offset = first_offset;

                        vm_object_lock(object);
                        /*
                         * get rid of the place holder
                         * page that we soldered in earlier
                         */
                        VM_PAGE_FREE(first_m);
                        first_m = VM_PAGE_NULL;
                        
                        /*
                         * and replace it with the
                         * page we just copied into
                         */
                        assert(copy_m->busy);
                        vm_page_insert(copy_m, object, offset);
                        copy_m->dirty = TRUE;

                        m = copy_m;
                        /*
                         * Now that we've gotten the copy out of the
                         * way, let's try to collapse the top object.
                         * But we have to play ugly games with
                         * paging_in_progress to do that...
                         */     
                        vm_object_paging_end(object); 
                        vm_object_collapse(object, offset, TRUE);
                        vm_object_paging_begin(object);

                } else
                        *protection &= (~VM_PROT_WRITE);
        }
        /*
         * Now check whether the page needs to be pushed into the
         * copy object.  The use of asymmetric copy on write for
         * shared temporary objects means that we may do two copies to
         * satisfy the fault; one above to get the page from a
         * shadowed object, and one here to push it into the copy.
         */
        try_failed_count = 0;

        while ((copy_object = first_object->copy) != VM_OBJECT_NULL && (m != VM_PAGE_NULL)) {
                vm_object_offset_t      copy_offset;
                vm_page_t               copy_m;

#if TRACEFAULTPAGE
                dbgTrace(0xBEEF0017, (unsigned int) copy_object, (unsigned int) fault_type);    /* (TEST/DEBUG) */
#endif
                /*
                 * If the page is being written, but hasn't been
                 * copied to the copy-object, we have to copy it there.
                 */
                if ((fault_type & VM_PROT_WRITE) == 0) {
                        *protection &= ~VM_PROT_WRITE;
                        break;
                }

                /*
                 * If the page was guaranteed to be resident,
                 * we must have already performed the copy.
                 */
                if (must_be_resident)
                        break;

                /*
                 * Try to get the lock on the copy_object.
                 */
                if (!vm_object_lock_try(copy_object)) {

                        vm_object_unlock(object);
                        try_failed_count++;

                        mutex_pause(try_failed_count);  /* wait a bit */
                        vm_object_lock(object);

                        continue;
                }
                try_failed_count = 0;

                /*
                 * Make another reference to the copy-object,
                 * to keep it from disappearing during the
                 * copy.
                 */
                vm_object_reference_locked(copy_object);

                /*
                 * Does the page exist in the copy?
                 */
                copy_offset = first_offset - copy_object->shadow_offset;

                if (copy_object->size <= copy_offset)
                        /*
                         * Copy object doesn't cover this page -- do nothing.
                         */
                        ;
                else if ((copy_m = vm_page_lookup(copy_object, copy_offset)) != VM_PAGE_NULL) {
                        /*
                         * Page currently exists in the copy object
                         */
                        if (copy_m->busy) {
                                /*
                                 * If the page is being brought
                                 * in, wait for it and then retry.
                                 */
                                RELEASE_PAGE(m);

                                /*
                                 * take an extra ref so object won't die
                                 */
                                vm_object_reference_locked(copy_object);
                                vm_object_unlock(copy_object);
                                vm_fault_cleanup(object, first_m);
                                counter(c_vm_fault_page_block_backoff_kernel++);

                                vm_object_lock(copy_object);
                                assert(copy_object->ref_count > 0);
                                VM_OBJ_RES_DECR(copy_object);
                                vm_object_lock_assert_exclusive(copy_object);
                                copy_object->ref_count--;
                                assert(copy_object->ref_count > 0);
                                copy_m = vm_page_lookup(copy_object, copy_offset);
                                /*
                                 * ENCRYPTED SWAP:
                                 * it's OK if the "copy_m" page is encrypted,
                                 * because we're not moving it nor handling its
                                 * contents.
                                 */
                                if (copy_m != VM_PAGE_NULL && copy_m->busy) {
                                        PAGE_ASSERT_WAIT(copy_m, interruptible);

                                        vm_object_unlock(copy_object);
                                        wait_result = thread_block(THREAD_CONTINUE_NULL);
                                        vm_object_deallocate(copy_object);

                                        goto backoff;
                                } else {
                                        vm_object_unlock(copy_object);
                                        vm_object_deallocate(copy_object);
                                        thread_interrupt_level(interruptible_state);

                                        return (VM_FAULT_RETRY);
                                }
                        }
                }
                else if (!PAGED_OUT(copy_object, copy_offset)) {
                        /*
                         * If PAGED_OUT is TRUE, then the page used to exist
                         * in the copy-object, and has already been paged out.
                         * We don't need to repeat this. If PAGED_OUT is
                         * FALSE, then either we don't know (!pager_created,
                         * for example) or it hasn't been paged out.
                         * (VM_EXTERNAL_STATE_UNKNOWN||VM_EXTERNAL_STATE_ABSENT)
                         * We must copy the page to the copy object.
                         */

                        if (vm_backing_store_low) {
                                /*
                                 * we are protecting the system from
                                 * backing store exhaustion.  If so
                                 * sleep unless we are privileged.
                                 */
                                if (!(current_task()->priv_flags & VM_BACKING_STORE_PRIV)) {
                                        assert_wait((event_t)&vm_backing_store_low, THREAD_UNINT);

                                        RELEASE_PAGE(m);
                                        VM_OBJ_RES_DECR(copy_object);
                                        vm_object_lock_assert_exclusive(copy_object);
                                        copy_object->ref_count--;
                                        assert(copy_object->ref_count > 0);

                                        vm_object_unlock(copy_object);
                                        vm_fault_cleanup(object, first_m);
                                        thread_block(THREAD_CONTINUE_NULL);
                                        thread_interrupt_level(interruptible_state);

                                        return (VM_FAULT_RETRY);
                                }
                        }
                        /*
                         * Allocate a page for the copy
                         */
                        copy_m = vm_page_alloc(copy_object, copy_offset);

                        if (copy_m == VM_PAGE_NULL) {
                                RELEASE_PAGE(m);

                                VM_OBJ_RES_DECR(copy_object);
                                vm_object_lock_assert_exclusive(copy_object);
                                copy_object->ref_count--;
                                assert(copy_object->ref_count > 0);

                                vm_object_unlock(copy_object);
                                vm_fault_cleanup(object, first_m);
                                thread_interrupt_level(interruptible_state);

                                return (VM_FAULT_MEMORY_SHORTAGE);
                        }
                        /*
                         * Must copy page into copy-object.
                         */
                        vm_page_copy(m, copy_m);
                        
                        /*
                         * If the old page was in use by any users
                         * of the copy-object, it must be removed
                         * from all pmaps.  (We can't know which
                         * pmaps use it.)
                         */
                        if (m->pmapped)
                                pmap_disconnect(m->phys_page);

                        /*
                         * If there's a pager, then immediately
                         * page out this page, using the "initialize"
                         * option.  Else, we use the copy.
                         */
                        if ((!copy_object->pager_created)
#if MACH_PAGEMAP
                            || vm_external_state_get(copy_object->existence_map, copy_offset) == VM_EXTERNAL_STATE_ABSENT
#endif
                            ) {

                                vm_page_lockspin_queues();
                                assert(!m->cleaning);
                                vm_page_activate(copy_m);
                                vm_page_unlock_queues();

                                copy_m->dirty = TRUE;
                                PAGE_WAKEUP_DONE(copy_m);
                        } 
                        else {
                                assert(copy_m->busy == TRUE);
                                assert(!m->cleaning);

                                /*
                                 * dirty is protected by the object lock
                                 */
                                copy_m->dirty = TRUE;

                                /*
                                 * The page is already ready for pageout:
                                 * not on pageout queues and busy.
                                 * Unlock everything except the
                                 * copy_object itself.
                                 */
                                vm_object_unlock(object);

                                /*
                                 * Write the page to the copy-object,
                                 * flushing it from the kernel.
                                 */
                                vm_pageout_initialize_page(copy_m);

                                /*
                                 * Since the pageout may have
                                 * temporarily dropped the
                                 * copy_object's lock, we
                                 * check whether we'll have
                                 * to deallocate the hard way.
                                 */
                                if ((copy_object->shadow != object) || (copy_object->ref_count == 1)) {
                                        vm_object_unlock(copy_object);
                                        vm_object_deallocate(copy_object);
                                        vm_object_lock(object);

                                        continue;
                                }
                                /*
                                 * Pick back up the old object's
                                 * lock.  [It is safe to do so,
                                 * since it must be deeper in the
                                 * object tree.]
                                 */
                                vm_object_lock(object);
                        }
                        /*
                         * Because we're pushing a page upward
                         * in the object tree, we must restart
                         * any faults that are waiting here.
                         * [Note that this is an expansion of
                         * PAGE_WAKEUP that uses the THREAD_RESTART
                         * wait result].  Can't turn off the page's
                         * busy bit because we're not done with it.
                         */
                        if (m->wanted) {
                                m->wanted = FALSE;
                                thread_wakeup_with_result((event_t) m, THREAD_RESTART);
                        }
                }
                /*
                 * The reference count on copy_object must be
                 * at least 2: one for our extra reference,
                 * and at least one from the outside world
                 * (we checked that when we last locked
                 * copy_object).
                 */
                vm_object_lock_assert_exclusive(copy_object);
                copy_object->ref_count--;
                assert(copy_object->ref_count > 0);

                VM_OBJ_RES_DECR(copy_object);   
                vm_object_unlock(copy_object);

                break;
        }
        *result_page = m;
        *top_page = first_m;

        XPR(XPR_VM_FAULT,
                "vm_f_page: DONE obj 0x%X, offset 0x%X, m 0x%X, first_m 0x%X\n",
                (integer_t)object, offset, (integer_t)m, (integer_t)first_m, 0);

        if (m != VM_PAGE_NULL) {
                if (my_fault == DBG_PAGEIN_FAULT) {

                        VM_STAT_INCR(pageins);
                        DTRACE_VM2(pgin, int, 1, (uint64_t *), NULL);
                        DTRACE_VM2(maj_fault, int, 1, (uint64_t *), NULL);
                        current_task()->pageins++;

                        if (m->object->internal) {
                                DTRACE_VM2(anonpgin, int, 1, (uint64_t *), NULL);
                        } else {
                                DTRACE_VM2(fspgin, int, 1, (uint64_t *), NULL);
                        }

                        /*
                         * evaluate access pattern and update state
                         * vm_fault_deactivate_behind depends on the
                         * state being up to date
                         */
                        vm_fault_is_sequential(object, offset, fault_info->behavior);

                        vm_fault_deactivate_behind(object, offset, fault_info->behavior);
                }
                if (type_of_fault)
                        *type_of_fault = my_fault;
        } else
                vm_object_unlock(object);

        thread_interrupt_level(interruptible_state);

#if TRACEFAULTPAGE
        dbgTrace(0xBEEF001A, (unsigned int) VM_FAULT_SUCCESS, 0);       /* (TEST/DEBUG) */
#endif
        return (VM_FAULT_SUCCESS);

backoff:
        thread_interrupt_level(interruptible_state);

        if (wait_result == THREAD_INTERRUPTED)
                return (VM_FAULT_INTERRUPTED);
        return (VM_FAULT_RETRY);

#undef  RELEASE_PAGE
}



/*
 * CODE SIGNING:
 * When soft faulting a page, we have to validate the page if:
 * 1. the page is being mapped in user space
 * 2. the page hasn't already been found to be "tainted"
 * 3. the page belongs to a code-signed object
 * 4. the page has not been validated yet or has been mapped for write.
 */
#define VM_FAULT_NEED_CS_VALIDATION(pmap, page)                         \
        ((pmap) != kernel_pmap /*1*/ &&                                 \
         !(page)->cs_tainted /*2*/ &&                                   \
         (page)->object->code_signed /*3*/ &&                           \
         (!(page)->cs_validated || (page)->wpmapped /*4*/))


/*
 * page queue lock must NOT be held
 * m->object must be locked
 *
 * NOTE: m->object could be locked "shared" only if we are called
 * from vm_fault() as part of a soft fault.  If so, we must be
 * careful not to modify the VM object in any way that is not
 * legal under a shared lock...
 */
unsigned long cs_enter_tainted_rejected = 0;
unsigned long cs_enter_tainted_accepted = 0;
kern_return_t
vm_fault_enter(vm_page_t m,
               pmap_t pmap,
               vm_map_offset_t vaddr,
               vm_prot_t prot,
               boolean_t wired,
               boolean_t change_wiring,
               boolean_t no_cache,
               int *type_of_fault)
{
        unsigned int    cache_attr;
        kern_return_t   kr;
        boolean_t       previously_pmapped = m->pmapped;

        vm_object_lock_assert_held(m->object);
#if DEBUG
        mutex_assert(&vm_page_queue_lock, MA_NOTOWNED);
#endif /* DEBUG */

        if (m->phys_page == vm_page_guard_addr) {
                assert(m->fictitious);
                return KERN_SUCCESS;
        }

        cache_attr = ((unsigned int)m->object->wimg_bits) & VM_WIMG_MASK;

        if (m->pmapped == FALSE) {
                /*
                 * This is the first time this page is being
                 * mapped in an address space (pmapped == FALSE).
                 *
                 * Part of that page may still be in the data cache
                 * and not flushed to memory.  In case we end up
                 * accessing that page via the instruction cache,
                 * we need to ensure that the 2 caches are in sync.
                 */
                pmap_sync_page_data_phys(m->phys_page);

                if ((*type_of_fault == DBG_CACHE_HIT_FAULT) && m->clustered) {
                        /*
                         * found it in the cache, but this
                         * is the first fault-in of the page (m->pmapped == FALSE)
                         * so it must have come in as part of
                         * a cluster... account 1 pagein against it
                         */
                        VM_STAT_INCR(pageins);
                        DTRACE_VM2(pgin, int, 1, (uint64_t *), NULL);

                        if (m->object->internal) {
                                DTRACE_VM2(anonpgin, int, 1, (uint64_t *), NULL);
                        } else {
                                DTRACE_VM2(fspgin, int, 1, (uint64_t *), NULL);
                        }

                        current_task()->pageins++;

                        *type_of_fault = DBG_PAGEIN_FAULT;
                }
                VM_PAGE_CONSUME_CLUSTERED(m);

        } else if (cache_attr != VM_WIMG_DEFAULT)
                pmap_sync_page_attributes_phys(m->phys_page);

        if (*type_of_fault != DBG_COW_FAULT) {
                DTRACE_VM2(as_fault, int, 1, (uint64_t *), NULL);

                if (pmap == kernel_pmap) {
                        DTRACE_VM2(kernel_asflt, int, 1, (uint64_t *), NULL);
                }
        }

        if (VM_FAULT_NEED_CS_VALIDATION(pmap, m)) {
                vm_object_lock_assert_exclusive(m->object);

                if (m->cs_validated) {
                        vm_cs_revalidates++;
                }

                /* VM map is locked, so 1 ref will remain on VM object */
                vm_page_validate_cs(m);
        }

        if (m->cs_tainted       /* always invalidate a tainted page */
#if CONFIG_ENFORCE_SIGNED_CODE
            /*
             * Code Signing enforcement invalidates an executable page that
             * has no code directory, and thus could not be validated.
             */
            || ((prot & VM_PROT_EXECUTE) && !m->cs_validated )
#endif
                ) {
                /*
                 * CODE SIGNING:
                 * This page has been tainted and can not be trusted.
                 * Let's notify the current process and let it take any
                 * necessary precautions before we enter the tainted page
                 * into its address space.
                 */
                kr = KERN_SUCCESS;
#if CONFIG_ENFORCE_SIGNED_CODE
                if (!cs_enforcement_disable) {
#endif
                        if (cs_invalid_page((addr64_t) vaddr)) {
                                /* reject the tainted page: abort the page fault */
                                kr = KERN_MEMORY_ERROR;
                                cs_enter_tainted_rejected++;
                        } else {
                                /* proceed with the tainted page */
                                kr = KERN_SUCCESS;
                                cs_enter_tainted_accepted++;
                        }
#if CONFIG_ENFORCE_SIGNED_CODE
                }
#endif
                if (cs_debug || kr != KERN_SUCCESS) {
                        printf("CODESIGNING: vm_fault_enter(0x%llx): "
                               "page %p obj %p off 0x%llx *** INVALID PAGE ***\n",
                               (long long)vaddr, m, m->object, m->offset);
                }
        } else {
                /* proceed with the valid page */
                kr = KERN_SUCCESS;
        }

        if (kr == KERN_SUCCESS) {
                /*
                 * NOTE: we may only hold the vm_object lock SHARED
                 * at this point, but the update of pmapped is ok
                 * since this is the ONLY bit updated behind the SHARED
                 * lock... however, we need to figure out how to do an atomic
                 * update on a bit field to make this less fragile... right
                 * now I don't know how to coerce 'C' to give me the offset info
                 * that's needed for an AtomicCompareAndSwap
                 */
                m->pmapped = TRUE;
                if (prot & VM_PROT_WRITE) {
                        vm_object_lock_assert_exclusive(m->object);
                        m->wpmapped = TRUE;
                }

                PMAP_ENTER(pmap, vaddr, m, prot, cache_attr, wired);
        }

        /*
         * Hold queues lock to manipulate
         * the page queues.  Change wiring
         * case is obvious.
         */
        if (change_wiring) {
                vm_page_lockspin_queues();

                if (wired) {
                        if (kr == KERN_SUCCESS) {
                                vm_page_wire(m);
                        }
                } else {
                        vm_page_unwire(m);
                }
                vm_page_unlock_queues();

        } else {
                if (kr != KERN_SUCCESS) {
                        vm_page_lock_queues();
                        vm_page_deactivate(m);
                        vm_page_unlock_queues();
                } else {
                        if (((!m->active && !m->inactive) || no_cache) && !m->wire_count && !m->throttled) {
                                vm_page_lockspin_queues();
                                /*
                                 * test again now that we hold the page queue lock
                                 */
                                if (((!m->active && !m->inactive) || no_cache) && !m->wire_count) {

                                        /*
                                         * If this is a no_cache mapping and the page has never been
                                         * mapped before or was previously a no_cache page, then we
                                         * want to leave pages in the speculative state so that they
                                         * can be readily recycled if free memory runs low.  Otherwise
                                         * the page is activated as normal. 
                                         */

                                        if (no_cache && (!previously_pmapped || m->no_cache)) {
                                                m->no_cache = TRUE;

                                                if (m->active || m->inactive)
                                                        VM_PAGE_QUEUES_REMOVE(m);

                                                if (!m->speculative) 
                                                        vm_page_speculate(m, TRUE);

                                        } else if (!m->active && !m->inactive)
                                                vm_page_activate(m);

                                }

                                vm_page_unlock_queues();
                        }
                }
        }
        return kr;
}


/*
 *      Routine:        vm_fault
 *      Purpose:
 *              Handle page faults, including pseudo-faults
 *              used to change the wiring status of pages.
 *      Returns:
 *              Explicit continuations have been removed.
 *      Implementation:
 *              vm_fault and vm_fault_page save mucho state
 *              in the moral equivalent of a closure.  The state
 *              structure is allocated when first entering vm_fault
 *              and deallocated when leaving vm_fault.
 */

extern int _map_enter_debug;

unsigned long vm_fault_collapse_total = 0;
unsigned long vm_fault_collapse_skipped = 0;

kern_return_t
vm_fault(
        vm_map_t        map,
        vm_map_offset_t vaddr,
        vm_prot_t       fault_type,
        boolean_t       change_wiring,
        int             interruptible,
        pmap_t          caller_pmap,
        vm_map_offset_t caller_pmap_addr)
{
        vm_map_version_t        version;        /* Map version for verificiation */
        boolean_t               wired;          /* Should mapping be wired down? */
        vm_object_t             object;         /* Top-level object */
        vm_object_offset_t      offset;         /* Top-level offset */
        vm_prot_t               prot;           /* Protection for mapping */
        vm_object_t             old_copy_object; /* Saved copy object */
        vm_page_t               result_page;    /* Result of vm_fault_page */
        vm_page_t               top_page;       /* Placeholder page */
        kern_return_t           kr;

        vm_page_t               m;      /* Fast access to result_page */
        kern_return_t           error_code;
        vm_object_t             cur_object;
        vm_object_offset_t      cur_offset;
        vm_page_t               cur_m;
        vm_object_t             new_object;
        int                     type_of_fault;
        pmap_t                  pmap;
        boolean_t               interruptible_state;
        vm_map_t                real_map = map;
        vm_map_t                original_map = map;
        vm_prot_t               original_fault_type;
        struct vm_object_fault_info fault_info;
        boolean_t               need_collapse = FALSE;
        int                     object_lock_type = 0;
        int                     cur_object_lock_type;


        KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, 2)) | DBG_FUNC_START,
                              (int)((uint64_t)vaddr >> 32),
                              (int)vaddr,
                              0,
                              0,
                              0);

        if (get_preemption_level() != 0) {
                KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, 2)) | DBG_FUNC_END,
                                      (int)((uint64_t)vaddr >> 32),
                                      (int)vaddr,
                                      KERN_FAILURE,
                                      0,
                                      0);

                return (KERN_FAILURE);
        }
        interruptible_state = thread_interrupt_level(interruptible);

        VM_STAT_INCR(faults);
        current_task()->faults++;
        original_fault_type = fault_type;

        if (fault_type & VM_PROT_WRITE)
                object_lock_type = OBJECT_LOCK_EXCLUSIVE;
        else
                object_lock_type = OBJECT_LOCK_SHARED;

        cur_object_lock_type = OBJECT_LOCK_SHARED;

RetryFault:
        /*
         * assume we will hit a page in the cache
         * otherwise, explicitly override with
         * the real fault type once we determine it
         */
        type_of_fault = DBG_CACHE_HIT_FAULT;

        /*
         *      Find the backing store object and offset into
         *      it to begin the search.
         */
        fault_type = original_fault_type;
        map = original_map;
        vm_map_lock_read(map);

        kr = vm_map_lookup_locked(&map, vaddr, fault_type,
                                  object_lock_type, &version,
                                  &object, &offset, &prot, &wired,
                                  &fault_info,
                                  &real_map);

        if (kr != KERN_SUCCESS) {
                vm_map_unlock_read(map);
                goto done;
        }
        pmap = real_map->pmap;
        fault_info.interruptible = interruptible;

        /*
         * If the page is wired, we must fault for the current protection
         * value, to avoid further faults.
         */
        if (wired) {
                fault_type = prot | VM_PROT_WRITE;
                /*
                 * since we're treating this fault as a 'write'
                 * we must hold the top object lock exclusively
                 */
                if (object_lock_type == OBJECT_LOCK_SHARED) {

                        object_lock_type = OBJECT_LOCK_EXCLUSIVE;

                        if (vm_object_lock_upgrade(object) == FALSE) {
                                /*
                                 * couldn't upgrade, so explictly
                                 * take the lock exclusively
                                 */
                                vm_object_lock(object);
                        }
                }
        }

#if     VM_FAULT_CLASSIFY
        /*
         *      Temporary data gathering code
         */
        vm_fault_classify(object, offset, fault_type);
#endif
        /*
         *      Fast fault code.  The basic idea is to do as much as
         *      possible while holding the map lock and object locks.
         *      Busy pages are not used until the object lock has to
         *      be dropped to do something (copy, zero fill, pmap enter).
         *      Similarly, paging references aren't acquired until that
         *      point, and object references aren't used.
         *
         *      If we can figure out what to do
         *      (zero fill, copy on write, pmap enter) while holding
         *      the locks, then it gets done.  Otherwise, we give up,
         *      and use the original fault path (which doesn't hold
         *      the map lock, and relies on busy pages).
         *      The give up cases include:
         *              - Have to talk to pager.
         *              - Page is busy, absent or in error.
         *              - Pager has locked out desired access.
         *              - Fault needs to be restarted.
         *              - Have to push page into copy object.
         *
         *      The code is an infinite loop that moves one level down
         *      the shadow chain each time.  cur_object and cur_offset
         *      refer to the current object being examined. object and offset
         *      are the original object from the map.  The loop is at the
         *      top level if and only if object and cur_object are the same.
         *
         *      Invariants:  Map lock is held throughout.  Lock is held on
         *              original object and cur_object (if different) when
         *              continuing or exiting loop.
         *
         */


        /*
         * If this page is to be inserted in a copy delay object
         * for writing, and if the object has a copy, then the
         * copy delay strategy is implemented in the slow fault page.
         */
        if (object->copy_strategy == MEMORY_OBJECT_COPY_DELAY &&
            object->copy != VM_OBJECT_NULL && (fault_type & VM_PROT_WRITE))
                goto handle_copy_delay;

        cur_object = object;
        cur_offset = offset;

        while (TRUE) {
                m = vm_page_lookup(cur_object, cur_offset);

                if (m != VM_PAGE_NULL) {
                        if (m->busy) {
                                wait_result_t   result;

                                /*
                                 * in order to do the PAGE_ASSERT_WAIT, we must
                                 * have object that 'm' belongs to locked exclusively
                                 */
                                if (object != cur_object) {
                                        vm_object_unlock(object);

                                        if (cur_object_lock_type == OBJECT_LOCK_SHARED) {

                                                cur_object_lock_type = OBJECT_LOCK_EXCLUSIVE;

                                                if (vm_object_lock_upgrade(cur_object) == FALSE) {
                                                        /*
                                                         * couldn't upgrade so go do a full retry
                                                         * immediately since we've already dropped
                                                         * the top object lock associated with this page
                                                         * and the current one got dropped due to the
                                                         * failed upgrade... the state is no longer valid
                                                         */
                                                        vm_map_unlock_read(map);
                                                        if (real_map != map)
                                                                vm_map_unlock(real_map);

                                                        goto RetryFault;
                                                }
                                        }
                                } else if (object_lock_type == OBJECT_LOCK_SHARED) {

                                        object_lock_type = OBJECT_LOCK_EXCLUSIVE;

                                        if (vm_object_lock_upgrade(object) == FALSE) {
                                                /*
                                                 * couldn't upgrade, so explictly take the lock
                                                 * exclusively and go relookup the page since we
                                                 * will have dropped the object lock and
                                                 * a different thread could have inserted
                                                 * a page at this offset
                                                 * no need for a full retry since we're
                                                 * at the top level of the object chain
                                                 */
                                                vm_object_lock(object);

                                                continue;
                                        }
                                }
                                vm_map_unlock_read(map);
                                if (real_map != map)
                                        vm_map_unlock(real_map);

                                result = PAGE_ASSERT_WAIT(m, interruptible);

                                vm_object_unlock(cur_object);

                                if (result == THREAD_WAITING) {
                                        result = thread_block(THREAD_CONTINUE_NULL);

                                        counter(c_vm_fault_page_block_busy_kernel++);
                                }
                                if (result == THREAD_AWAKENED || result == THREAD_RESTART)
                                        goto RetryFault;

                                kr = KERN_ABORTED;
                                goto done;
                        }
                        if (m->phys_page == vm_page_guard_addr) {
                                /*
                                 * Guard page: let the slow path deal with it
                                 */
                                break;
                        }
                        if (m->unusual && (m->error || m->restart || m->private || m->absent)) {
                                /*
                                 * Unusual case... let the slow path deal with it
                                 */
                                break;
                        }
                        if (m->encrypted) {
                                /*
                                 * ENCRYPTED SWAP:
                                 * We've soft-faulted (because it's not in the page
                                 * table) on an encrypted page.
                                 * Keep the page "busy" so that no one messes with
                                 * it during the decryption.
                                 * Release the extra locks we're holding, keep only
                                 * the page's VM object lock.
                                 *
                                 * in order to set 'busy' on 'm', we must
                                 * have object that 'm' belongs to locked exclusively
                                 */
                                if (object != cur_object) {
                                        vm_object_unlock(object);

                                        if (cur_object_lock_type == OBJECT_LOCK_SHARED) {

                                                cur_object_lock_type = OBJECT_LOCK_EXCLUSIVE;

                                                if (vm_object_lock_upgrade(cur_object) == FALSE) {
                                                        /*
                                                         * couldn't upgrade so go do a full retry
                                                         * immediately since we've already dropped
                                                         * the top object lock associated with this page
                                                         * and the current one got dropped due to the
                                                         * failed upgrade... the state is no longer valid
                                                         */
                                                        vm_map_unlock_read(map);
                                                        if (real_map != map)
                                                                vm_map_unlock(real_map);

                                                        goto RetryFault;
                                                }
                                        }
                                } else if (object_lock_type == OBJECT_LOCK_SHARED) {

                                        object_lock_type = OBJECT_LOCK_EXCLUSIVE;

                                        if (vm_object_lock_upgrade(object) == FALSE) {
                                                /*
                                                 * couldn't upgrade, so explictly take the lock
                                                 * exclusively and go relookup the page since we
                                                 * will have dropped the object lock and
                                                 * a different thread could have inserted
                                                 * a page at this offset
                                                 * no need for a full retry since we're
                                                 * at the top level of the object chain
                                                 */
                                                vm_object_lock(object);

                                                continue;
                                        }
                                }
                                m->busy = TRUE;

                                vm_map_unlock_read(map);
                                if (real_map != map) 
                                        vm_map_unlock(real_map);

                                vm_page_decrypt(m, 0);

                                assert(m->busy);
                                PAGE_WAKEUP_DONE(m);

                                vm_object_unlock(cur_object);
                                /*
                                 * Retry from the top, in case anything
                                 * changed while we were decrypting...
                                 */
                                goto RetryFault;
                        }
                        ASSERT_PAGE_DECRYPTED(m);

                        if (VM_FAULT_NEED_CS_VALIDATION(map->pmap, m)) {
                                /*
                                 * We might need to validate this page
                                 * against its code signature, so we
                                 * want to hold the VM object exclusively.
                                 */
                                if (object != cur_object) {
                                        if (cur_object_lock_type == OBJECT_LOCK_SHARED) {
                                                vm_object_unlock(object);
                                                vm_object_unlock(cur_object);

                                                cur_object_lock_type = OBJECT_LOCK_EXCLUSIVE;

                                                vm_map_unlock_read(map);
                                                if (real_map != map)
                                                        vm_map_unlock(real_map);

                                                goto RetryFault;
                                        }

                                } else if (object_lock_type == OBJECT_LOCK_SHARED) {

                                        object_lock_type = OBJECT_LOCK_EXCLUSIVE;

                                        if (vm_object_lock_upgrade(object) == FALSE) {
                                                /*
                                                 * couldn't upgrade, so explictly take the lock
                                                 * exclusively and go relookup the page since we
                                                 * will have dropped the object lock and
                                                 * a different thread could have inserted
                                                 * a page at this offset
                                                 * no need for a full retry since we're
                                                 * at the top level of the object chain
                                                 */
                                                vm_object_lock(object);

                                                continue;
                                        }
                                }
                        }
                        /*
                         *      Two cases of map in faults:
                         *          - At top level w/o copy object.
                         *          - Read fault anywhere.
                         *              --> must disallow write.
                         */

                        if (object == cur_object && object->copy == VM_OBJECT_NULL) {
                                if ((fault_type & VM_PROT_WRITE) == 0) {
                                        /*
                                         * This is not a "write" fault, so we
                                         * might not have taken the object lock
                                         * exclusively and we might not be able
                                         * to update the "wpmapped" bit in
                                         * vm_fault_enter().
                                         * Let's just grant read access to
                                         * the page for now and we'll
                                         * soft-fault again if we need write
                                         * access later...
                                         */
                                        prot &= ~VM_PROT_WRITE;
                                }
                                goto FastPmapEnter;
                        }

                        if ((fault_type & VM_PROT_WRITE) == 0) {

                                prot &= ~VM_PROT_WRITE;

                                /*
                                 * Set up to map the page...
                                 * mark the page busy, drop
                                 * unneeded object lock
                                 */     
                                if (object != cur_object) {
                                        /*      
                                         * don't need the original object anymore
                                         */
                                        vm_object_unlock(object);

                                        /*
                                         * switch to the object that has the new page
                                         */
                                        object = cur_object;
                                        object_lock_type = cur_object_lock_type;
                                }
FastPmapEnter:
                                /*
                                 * prepare for the pmap_enter...
                                 * object and map are both locked
                                 * m contains valid data
                                 * object == m->object
                                 * cur_object == NULL or it's been unlocked
                                 * no paging references on either object or cur_object
                                 */
#if     MACH_KDB
                                if (db_watchpoint_list && (fault_type & VM_PROT_WRITE) == 0)
                                        prot &= ~VM_PROT_WRITE;
#endif
                                if (caller_pmap) {
                                        kr = vm_fault_enter(m,
                                                            caller_pmap,
                                                            caller_pmap_addr,
                                                            prot,
                                                            wired,
                                                            change_wiring,
                                                            fault_info.no_cache,
                                                            &type_of_fault);
                                } else {
                                        kr = vm_fault_enter(m,
                                                            pmap,
                                                            vaddr,
                                                            prot,
                                                            wired,
                                                            change_wiring,
                                                            fault_info.no_cache,
                                                            &type_of_fault);
                                }

                                if (need_collapse == TRUE)
                                        vm_object_collapse(object, offset, TRUE);

                                if (type_of_fault == DBG_PAGEIN_FAULT) {
                                        /*
                                         * evaluate access pattern and update state
                                         * vm_fault_deactivate_behind depends on the
                                         * state being up to date
                                         */
                                        vm_fault_is_sequential(object, cur_offset, fault_info.behavior);

                                        vm_fault_deactivate_behind(object, cur_offset, fault_info.behavior);
                                }
                                /*
                                 * That's it, clean up and return.
                                 */
                                if (m->busy)
                                        PAGE_WAKEUP_DONE(m);

                                vm_object_unlock(object);

                                vm_map_unlock_read(map);
                                if (real_map != map)
                                        vm_map_unlock(real_map);

                                goto done;
                        }
                        /*
                         * COPY ON WRITE FAULT
                         *
                         * If objects match, then
                         * object->copy must not be NULL (else control
                         * would be in previous code block), and we
                         * have a potential push into the copy object
                         * with which we can't cope with here.
                         */
                        if (cur_object == object) {
                                /*
                                 * must take the slow path to
                                 * deal with the copy push
                                 */
                                break;
                        }
                        assert(object_lock_type == OBJECT_LOCK_EXCLUSIVE);

                        /*
                         * This is now a shadow based copy on write
                         * fault -- it requires a copy up the shadow
                         * chain.
                         *
                         * Allocate a page in the original top level
                         * object. Give up if allocate fails.  Also
                         * need to remember current page, as it's the
                         * source of the copy.
                         *
                         * at this point we hold locks on both 
                         * object and cur_object... no need to take
                         * paging refs or mark pages BUSY since
                         * we don't drop either object lock until
                         * the page has been copied and inserted
                         */
                        cur_m = m;
                        m = vm_page_grab();

                        if (m == VM_PAGE_NULL) {
                                /*
                                 * no free page currently available...
                                 * must take the slow path
                                 */
                                break;
                        }
                        /*
                         * Now do the copy.  Mark the source page busy...
                         *
                         *      NOTE: This code holds the map lock across
                         *      the page copy.
                         */
                        vm_page_copy(cur_m, m);
                        vm_page_insert(m, object, offset);
                        m->dirty = TRUE;

                        /*
                         * Now cope with the source page and object
                         */
                        if (object->ref_count > 1 && cur_m->pmapped)
                                pmap_disconnect(cur_m->phys_page);

                        need_collapse = TRUE;

                        if (!cur_object->internal &&
                            cur_object->copy_strategy == MEMORY_OBJECT_COPY_DELAY) {
                                /*
                                 * The object from which we've just
                                 * copied a page is most probably backed
                                 * by a vnode.  We don't want to waste too
                                 * much time trying to collapse the VM objects
                                 * and create a bottleneck when several tasks
                                 * map the same file.
                                 */
                                if (cur_object->copy == object) {
                                        /*
                                         * Shared mapping or no COW yet.
                                         * We can never collapse a copy
                                         * object into its backing object.
                                         */
                                        need_collapse = FALSE;
                                } else if (cur_object->copy == object->shadow &&
                                           object->shadow->resident_page_count == 0) {
                                        /*
                                         * Shared mapping after a COW occurred.
                                         */
                                        need_collapse = FALSE;
                                }
                        }
                        vm_object_unlock(cur_object);

                        if (need_collapse == FALSE)
                                vm_fault_collapse_skipped++;
                        vm_fault_collapse_total++;

                        type_of_fault = DBG_COW_FAULT;
                        VM_STAT_INCR(cow_faults);
                        DTRACE_VM2(cow_fault, int, 1, (uint64_t *), NULL);
                        current_task()->cow_faults++;

                        goto FastPmapEnter;

                } else {
                        /*
                         * No page at cur_object, cur_offset... m == NULL
                         */
                        if (cur_object->pager_created) {
                                if (MUST_ASK_PAGER(cur_object, cur_offset) == TRUE) {
                                        /*
                                         * May have to talk to a pager...
                                         * take the slow path.
                                         */
                                        break;
                                }
                                /*
                                 * existence map present and indicates
                                 * that the pager doesn't have this page
                                 */
                        }
                        if (cur_object->shadow == VM_OBJECT_NULL) {
                                /*
                                 * Zero fill fault.  Page gets
                                 * inserted into the original object.
                                 */
                                if (cur_object->shadow_severed) {

                                        if (object != cur_object)
                                                vm_object_unlock(cur_object);
                                        vm_object_unlock(object);

                                        vm_map_unlock_read(map);
                                        if (real_map != map)
                                                vm_map_unlock(real_map);

                                        kr = KERN_MEMORY_ERROR;
                                        goto done;
                                }
                                if (VM_PAGE_ZFILL_THROTTLED()) {
                                        /*
                                         * drop all of our locks...
                                         * wait until the free queue is
                                         * pumped back up and then
                                         * redrive the fault
                                         */
                                        if (object != cur_object)
                                                vm_object_unlock(cur_object);
                                        vm_object_unlock(object);
                                        vm_map_unlock_read(map);
                                        if (real_map != map)
                                                vm_map_unlock(real_map);

                                        if (vm_page_wait((change_wiring) ? 
                                                         THREAD_UNINT :
                                                         THREAD_ABORTSAFE))
                                                goto RetryFault;

                                        kr = KERN_ABORTED;
                                        goto done;
                                }
                                if (vm_backing_store_low) {
                                        /*
                                         * we are protecting the system from
                                         * backing store exhaustion... 
                                         * must take the slow path if we're
                                         * not privileged
                                         */
                                        if (!(current_task()->priv_flags & VM_BACKING_STORE_PRIV))
                                                break;
                                }
                                if (cur_object != object) {
                                        vm_object_unlock(cur_object);

                                        cur_object = object;
                                }
                                if (object_lock_type == OBJECT_LOCK_SHARED) {

                                        object_lock_type = OBJECT_LOCK_EXCLUSIVE;

                                        if (vm_object_lock_upgrade(object) == FALSE) {
                                                /*
                                                 * couldn't upgrade so do a full retry on the fault
                                                 * since we dropped the object lock which
                                                 * could allow another thread to insert
                                                 * a page at this offset
                                                 */
                                                vm_map_unlock_read(map);
                                                if (real_map != map)
                                                        vm_map_unlock(real_map);

                                                goto RetryFault;
                                        }
                                }
                                m = vm_page_alloc(object, offset);

                                if (m == VM_PAGE_NULL) {
                                        /*
                                         * no free page currently available...
                                         * must take the slow path
                                         */
                                        break;
                                }

                                /*
                                 * Now zero fill page...
                                 * the page is probably going to 
                                 * be written soon, so don't bother
                                 * to clear the modified bit
                                 *
                                 *   NOTE: This code holds the map
                                 *   lock across the zero fill.
                                 */
                                type_of_fault = vm_fault_zero_page(m, map->no_zero_fill);

                                goto FastPmapEnter;
                        }
                        /*
                         * On to the next level in the shadow chain
                         */
                        cur_offset += cur_object->shadow_offset;
                        new_object = cur_object->shadow;

                        /*
                         * take the new_object's lock with the indicated state
                         */
                        if (cur_object_lock_type == OBJECT_LOCK_SHARED)
                                vm_object_lock_shared(new_object);
                        else
                                vm_object_lock(new_object);

                        if (cur_object != object)
                                vm_object_unlock(cur_object);

                        cur_object = new_object;

                        continue;
                }
        }
        /*
         * Cleanup from fast fault failure.  Drop any object
         * lock other than original and drop map lock.
         */
        if (object != cur_object)
                vm_object_unlock(cur_object);

        /*
         * must own the object lock exclusively at this point
         */
        if (object_lock_type == OBJECT_LOCK_SHARED) {
                object_lock_type = OBJECT_LOCK_EXCLUSIVE;

                if (vm_object_lock_upgrade(object) == FALSE) {
                        /*
                         * couldn't upgrade, so explictly
                         * take the lock exclusively
                         * no need to retry the fault at this
                         * point since "vm_fault_page" will
                         * completely re-evaluate the state
                         */
                        vm_object_lock(object);
                }
        }

handle_copy_delay:
        vm_map_unlock_read(map);
        if (real_map != map)
                vm_map_unlock(real_map);

        /*
         * Make a reference to this object to
         * prevent its disposal while we are messing with
         * it.  Once we have the reference, the map is free
         * to be diddled.  Since objects reference their
         * shadows (and copies), they will stay around as well.
         */
        vm_object_reference_locked(object);
        vm_object_paging_begin(object);

        XPR(XPR_VM_FAULT,"vm_fault -> vm_fault_page\n",0,0,0,0,0);

        error_code = 0;

        kr = vm_fault_page(object, offset, fault_type,
                           (change_wiring && !wired),
                           &prot, &result_page, &top_page,
                           &type_of_fault,
                           &error_code, map->no_zero_fill,
                           FALSE, &fault_info);

        /*
         * if kr != VM_FAULT_SUCCESS, then the paging reference
         * has been dropped and the object unlocked... the ref_count
         * is still held
         *
         * if kr == VM_FAULT_SUCCESS, then the paging reference
         * is still held along with the ref_count on the original object
         *
         *      if m != NULL, then the object it belongs to 
         *      is returned locked with a paging reference
         *
         *      if top_page != NULL, then it's BUSY and the 
         *      object it belongs to has a paging reference
         *      but is returned unlocked
         */
        if (kr != VM_FAULT_SUCCESS) {
                /*
                 * we didn't succeed, lose the object reference immediately.
                 */
                vm_object_deallocate(object);

                /*
                 * See why we failed, and take corrective action.
                 */
                switch (kr) {
                case VM_FAULT_MEMORY_SHORTAGE:
                        if (vm_page_wait((change_wiring) ? 
                                         THREAD_UNINT :
                                         THREAD_ABORTSAFE))
                                goto RetryFault;
                        /*
                         * fall thru
                         */
                case VM_FAULT_INTERRUPTED:
                        kr = KERN_ABORTED;
                        goto done;
                case VM_FAULT_RETRY:
                        goto RetryFault;
                case VM_FAULT_MEMORY_ERROR:
                        if (error_code)
                                kr = error_code;
                        else
                                kr = KERN_MEMORY_ERROR;
                        goto done;
                }
        }
        m = result_page;

        if (m != VM_PAGE_NULL) {
                assert((change_wiring && !wired) ?
                    (top_page == VM_PAGE_NULL) :
                    ((top_page == VM_PAGE_NULL) == (m->object == object)));
        }

        /*
         * What to do with the resulting page from vm_fault_page
         * if it doesn't get entered into the physical map:
         */
#define RELEASE_PAGE(m)                                 \
        MACRO_BEGIN                                     \
        PAGE_WAKEUP_DONE(m);                            \
        vm_page_lockspin_queues();                      \
        if (!m->active && !m->inactive && !m->throttled)\
                vm_page_activate(m);                    \
        vm_page_unlock_queues();                        \
        MACRO_END

        /*
         * We must verify that the maps have not changed
         * since our last lookup.
         */
        if (m != VM_PAGE_NULL) {
                old_copy_object = m->object->copy;
                vm_object_unlock(m->object);
        } else
                old_copy_object = VM_OBJECT_NULL;

        /*
         * no object locks are held at this point
         */
        if ((map != original_map) || !vm_map_verify(map, &version)) {
                vm_object_t             retry_object;
                vm_object_offset_t      retry_offset;
                vm_prot_t               retry_prot;

                /*
                 * To avoid trying to write_lock the map while another
                 * thread has it read_locked (in vm_map_pageable), we
                 * do not try for write permission.  If the page is
                 * still writable, we will get write permission.  If it
                 * is not, or has been marked needs_copy, we enter the
                 * mapping without write permission, and will merely
                 * take another fault.
                 */
                map = original_map;
                vm_map_lock_read(map);

                kr = vm_map_lookup_locked(&map, vaddr,
                                          fault_type & ~VM_PROT_WRITE,
                                          OBJECT_LOCK_EXCLUSIVE, &version,
                                          &retry_object, &retry_offset, &retry_prot,
                                          &wired,
                                          &fault_info,
                                          &real_map);
                pmap = real_map->pmap;

                if (kr != KERN_SUCCESS) {
                        vm_map_unlock_read(map);

                        if (m != VM_PAGE_NULL) {
                                /*
                                 * retake the lock so that
                                 * we can drop the paging reference
                                 * in vm_fault_cleanup and do the
                                 * PAGE_WAKEUP_DONE in RELEASE_PAGE
                                 */
                                vm_object_lock(m->object);

                                RELEASE_PAGE(m);

                                vm_fault_cleanup(m->object, top_page);
                        } else {
                                /*
                                 * retake the lock so that
                                 * we can drop the paging reference
                                 * in vm_fault_cleanup
                                 */
                                vm_object_lock(object);

                                vm_fault_cleanup(object, top_page);
                        }
                        vm_object_deallocate(object);

                        goto done;
                }
                vm_object_unlock(retry_object);

                if ((retry_object != object) || (retry_offset != offset)) {

                        vm_map_unlock_read(map);
                        if (real_map != map)
                                vm_map_unlock(real_map);

                        if (m != VM_PAGE_NULL) {
                                /*
                                 * retake the lock so that
                                 * we can drop the paging reference
                                 * in vm_fault_cleanup and do the
                                 * PAGE_WAKEUP_DONE in RELEASE_PAGE
                                 */
                                vm_object_lock(m->object);

                                RELEASE_PAGE(m);

                                vm_fault_cleanup(m->object, top_page);
                        } else {
                                /*
                                 * retake the lock so that
                                 * we can drop the paging reference
                                 * in vm_fault_cleanup
                                 */
                                vm_object_lock(object);

                                vm_fault_cleanup(object, top_page);
                        }
                        vm_object_deallocate(object);

                        goto RetryFault;
                }
                /*
                 * Check whether the protection has changed or the object
                 * has been copied while we left the map unlocked.
                 */
                prot &= retry_prot;
        }
        if (m != VM_PAGE_NULL) {
                vm_object_lock(m->object);

                if (m->object->copy != old_copy_object) {
                        /*
                         * The copy object changed while the top-level object
                         * was unlocked, so take away write permission.
                         */
                        prot &= ~VM_PROT_WRITE;
                }
        } else
                vm_object_lock(object);

        /*
         * If we want to wire down this page, but no longer have
         * adequate permissions, we must start all over.
         */
        if (wired && (fault_type != (prot | VM_PROT_WRITE))) {

                vm_map_verify_done(map, &version);
                if (real_map != map)
                        vm_map_unlock(real_map);

                if (m != VM_PAGE_NULL) {
                        RELEASE_PAGE(m);

                        vm_fault_cleanup(m->object, top_page);
                } else
                        vm_fault_cleanup(object, top_page);

                vm_object_deallocate(object);

                goto RetryFault;
        }
        if (m != VM_PAGE_NULL) {
                /*
                 * Put this page into the physical map.
                 * We had to do the unlock above because pmap_enter
                 * may cause other faults.  The page may be on
                 * the pageout queues.  If the pageout daemon comes
                 * across the page, it will remove it from the queues.
                 */
                if (caller_pmap) {
                        kr = vm_fault_enter(m,
                                            caller_pmap,
                                            caller_pmap_addr,
                                            prot,
                                            wired,
                                            change_wiring,
                                            fault_info.no_cache,
                                            &type_of_fault);
                } else {
                        kr = vm_fault_enter(m,
                                            pmap,
                                            vaddr,
                                            prot,
                                            wired,
                                            change_wiring,
                                            fault_info.no_cache,
                                            &type_of_fault);
                }
                if (kr != KERN_SUCCESS) {
                        /* abort this page fault */
                        vm_map_verify_done(map, &version);
                        if (real_map != map)
                                vm_map_unlock(real_map);
                        PAGE_WAKEUP_DONE(m);
                        vm_fault_cleanup(m->object, top_page);
                        vm_object_deallocate(object);
                        goto done;
                }
        } else {

                vm_map_entry_t          entry;
                vm_map_offset_t         laddr;
                vm_map_offset_t         ldelta, hdelta;

                /* 
                 * do a pmap block mapping from the physical address
                 * in the object 
                 */

#ifdef ppc
                /* While we do not worry about execution protection in   */
                /* general, certian pages may have instruction execution */
                /* disallowed.  We will check here, and if not allowed   */
                /* to execute, we return with a protection failure.      */

                if ((fault_type & VM_PROT_EXECUTE) &&
                        (!pmap_eligible_for_execute((ppnum_t)(object->shadow_offset >> 12)))) {

                        vm_map_verify_done(map, &version);

                        if (real_map != map)
                                vm_map_unlock(real_map);

                        vm_fault_cleanup(object, top_page);
                        vm_object_deallocate(object);

                        kr = KERN_PROTECTION_FAILURE;
                        goto done;
                }
#endif  /* ppc */

                if (real_map != map)
                        vm_map_unlock(real_map);

                if (original_map != map) {
                        vm_map_unlock_read(map);
                        vm_map_lock_read(original_map);
                        map = original_map;
                }
                real_map = map;

                laddr = vaddr;
                hdelta = 0xFFFFF000;
                ldelta = 0xFFFFF000;

                while (vm_map_lookup_entry(map, laddr, &entry)) {
                        if (ldelta > (laddr - entry->vme_start))
                                ldelta = laddr - entry->vme_start;
                        if (hdelta > (entry->vme_end - laddr))
                                hdelta = entry->vme_end - laddr;
                        if (entry->is_sub_map) {
                                
                                laddr = (laddr - entry->vme_start) 
                                                        + entry->offset;
                                vm_map_lock_read(entry->object.sub_map);

                                if (map != real_map)
                                        vm_map_unlock_read(map);
                                if (entry->use_pmap) {
                                        vm_map_unlock_read(real_map);
                                        real_map = entry->object.sub_map;
                                }
                                map = entry->object.sub_map;
                                
                        } else {
                                break;
                        }
                }

                if (vm_map_lookup_entry(map, laddr, &entry) && 
                                        (entry->object.vm_object != NULL) &&
                                        (entry->object.vm_object == object)) {

                        if (caller_pmap) {
                                /*
                                 * Set up a block mapped area
                                 */
                                pmap_map_block(caller_pmap, 
                                               (addr64_t)(caller_pmap_addr - ldelta), 
                                               (((vm_map_offset_t) (entry->object.vm_object->shadow_offset)) +
                                                entry->offset + (laddr - entry->vme_start) - ldelta) >> 12,
                                               ((ldelta + hdelta) >> 12), prot, 
                                               (VM_WIMG_MASK & (int)object->wimg_bits), 0);
                        } else { 
                                /*
                                 * Set up a block mapped area
                                 */
                                pmap_map_block(real_map->pmap, 
                                               (addr64_t)(vaddr - ldelta), 
                                               (((vm_map_offset_t)(entry->object.vm_object->shadow_offset)) +
                                                entry->offset + (laddr - entry->vme_start) - ldelta) >> 12,
                                               ((ldelta + hdelta) >> 12), prot, 
                                               (VM_WIMG_MASK & (int)object->wimg_bits), 0);
                        }
                }
        }

        /*
         * Unlock everything, and return
         */
        vm_map_verify_done(map, &version);
        if (real_map != map)
                vm_map_unlock(real_map);

        if (m != VM_PAGE_NULL) {
                PAGE_WAKEUP_DONE(m);

                vm_fault_cleanup(m->object, top_page);
        } else
                vm_fault_cleanup(object, top_page);

        vm_object_deallocate(object);

#undef  RELEASE_PAGE

        kr = KERN_SUCCESS;
done:
        thread_interrupt_level(interruptible_state);

        KERNEL_DEBUG_CONSTANT((MACHDBG_CODE(DBG_MACH_VM, 2)) | DBG_FUNC_END,
                              (int)((uint64_t)vaddr >> 32),
                              (int)vaddr,
                              kr,
                              type_of_fault,
                              0);

        return (kr);
}

/*
 *      vm_fault_wire:
 *
 *      Wire down a range of virtual addresses in a map.
 */
kern_return_t
vm_fault_wire(
        vm_map_t        map,
        vm_map_entry_t  entry,
        pmap_t          pmap,
        vm_map_offset_t pmap_addr)
{

        register vm_map_offset_t        va;
        register vm_map_offset_t        end_addr = entry->vme_end;
        register kern_return_t  rc;

        assert(entry->in_transition);

        if ((entry->object.vm_object != NULL) && 
                        !entry->is_sub_map && 
                        entry->object.vm_object->phys_contiguous) {
                return KERN_SUCCESS;
        }

        /*
         *      Inform the physical mapping system that the
         *      range of addresses may not fault, so that
         *      page tables and such can be locked down as well.
         */

        pmap_pageable(pmap, pmap_addr, 
                pmap_addr + (end_addr - entry->vme_start), FALSE);

        /*
         *      We simulate a fault to get the page and enter it
         *      in the physical map.
         */

        for (va = entry->vme_start; va < end_addr; va += PAGE_SIZE) {
                if ((rc = vm_fault_wire_fast(
                        map, va, entry, pmap, 
                        pmap_addr + (va - entry->vme_start)
                        )) != KERN_SUCCESS) {
                        rc = vm_fault(map, va, VM_PROT_NONE, TRUE, 
                                (pmap == kernel_pmap) ? 
                                        THREAD_UNINT : THREAD_ABORTSAFE, 
                                pmap, pmap_addr + (va - entry->vme_start));
                        DTRACE_VM2(softlock, int, 1, (uint64_t *), NULL);
                }

                if (rc != KERN_SUCCESS) {
                        struct vm_map_entry     tmp_entry = *entry;

                        /* unwire wired pages */
                        tmp_entry.vme_end = va;
                        vm_fault_unwire(map, 
                                &tmp_entry, FALSE, pmap, pmap_addr);

                        return rc;
                }
        }
        return KERN_SUCCESS;
}

/*
 *      vm_fault_unwire:
 *
 *      Unwire a range of virtual addresses in a map.
 */
void
vm_fault_unwire(
        vm_map_t        map,
        vm_map_entry_t  entry,
        boolean_t       deallocate,
        pmap_t          pmap,
        vm_map_offset_t pmap_addr)
{
        register vm_map_offset_t        va;
        register vm_map_offset_t        end_addr = entry->vme_end;
        vm_object_t             object;
        struct vm_object_fault_info fault_info;

        object = (entry->is_sub_map)
                        ? VM_OBJECT_NULL : entry->object.vm_object;

        /*
         * If it's marked phys_contiguous, then vm_fault_wire() didn't actually
         * do anything since such memory is wired by default.  So we don't have
         * anything to undo here.
         */

        if (object != VM_OBJECT_NULL && object->phys_contiguous)
                return;

        fault_info.interruptible = THREAD_UNINT;
        fault_info.behavior = entry->behavior;
        fault_info.user_tag = entry->alias;
        fault_info.lo_offset = entry->offset;
        fault_info.hi_offset = (entry->vme_end - entry->vme_start) + entry->offset;
        fault_info.no_cache = entry->no_cache;

        /*
         *      Since the pages are wired down, we must be able to
         *      get their mappings from the physical map system.
         */

        for (va = entry->vme_start; va < end_addr; va += PAGE_SIZE) {

                if (object == VM_OBJECT_NULL) {
                        if (pmap) {
                                pmap_change_wiring(pmap, 
                                                   pmap_addr + (va - entry->vme_start), FALSE);
                        }
                        (void) vm_fault(map, va, VM_PROT_NONE, 
                                        TRUE, THREAD_UNINT, pmap, pmap_addr);
                } else {
                        vm_prot_t       prot;
                        vm_page_t       result_page;
                        vm_page_t       top_page;
                        vm_object_t     result_object;
                        vm_fault_return_t result;

                        fault_info.cluster_size = end_addr - va;

                        do {
                                prot = VM_PROT_NONE;

                                vm_object_lock(object);
                                vm_object_paging_begin(object);
                                XPR(XPR_VM_FAULT,
                                        "vm_fault_unwire -> vm_fault_page\n",
                                        0,0,0,0,0);
                                result = vm_fault_page(
                                        object,
                                        entry->offset + (va - entry->vme_start),
                                        VM_PROT_NONE, TRUE,
                                        &prot, &result_page, &top_page,
                                        (int *)0,
                                        NULL, map->no_zero_fill, 
                                        FALSE, &fault_info);
                        } while (result == VM_FAULT_RETRY);

                        /*
                         * If this was a mapping to a file on a device that has been forcibly
                         * unmounted, then we won't get a page back from vm_fault_page().  Just
                         * move on to the next one in case the remaining pages are mapped from
                         * different objects.  During a forced unmount, the object is terminated
                         * so the alive flag will be false if this happens.  A forced unmount will
                         * will occur when an external disk is unplugged before the user does an 
                         * eject, so we don't want to panic in that situation.
                         */

                        if (result == VM_FAULT_MEMORY_ERROR && !object->alive)
                                continue;

                        if (result != VM_FAULT_SUCCESS)
                                panic("vm_fault_unwire: failure");

                        result_object = result_page->object;

                        if ((pmap) && (result_page->phys_page != vm_page_guard_addr)) {
                                pmap_change_wiring(pmap, 
                                                   pmap_addr + (va - entry->vme_start), FALSE);
                        }
                        if (deallocate) {
                                assert(result_page->phys_page !=
                                       vm_page_fictitious_addr);
                                pmap_disconnect(result_page->phys_page);
                                VM_PAGE_FREE(result_page);
                        } else {
                                vm_page_lockspin_queues();
                                vm_page_unwire(result_page);
                                vm_page_unlock_queues();
                                PAGE_WAKEUP_DONE(result_page);
                        }
                        vm_fault_cleanup(result_object, top_page);
                }
        }

        /*
         *      Inform the physical mapping system that the range
         *      of addresses may fault, so that page tables and
         *      such may be unwired themselves.
         */

        pmap_pageable(pmap, pmap_addr, 
                pmap_addr + (end_addr - entry->vme_start), TRUE);

}

/*
 *      vm_fault_wire_fast:
 *
 *      Handle common case of a wire down page fault at the given address.
 *      If successful, the page is inserted into the associated physical map.
 *      The map entry is passed in to avoid the overhead of a map lookup.
 *
 *      NOTE: the given address should be truncated to the
 *      proper page address.
 *
 *      KERN_SUCCESS is returned if the page fault is handled; otherwise,
 *      a standard error specifying why the fault is fatal is returned.
 *
 *      The map in question must be referenced, and remains so.
 *      Caller has a read lock on the map.
 *
 *      This is a stripped version of vm_fault() for wiring pages.  Anything
 *      other than the common case will return KERN_FAILURE, and the caller
 *      is expected to call vm_fault().
 */
kern_return_t
vm_fault_wire_fast(
        __unused vm_map_t       map,
        vm_map_offset_t va,
        vm_map_entry_t  entry,
        pmap_t                  pmap,
        vm_map_offset_t pmap_addr)
{
        vm_object_t             object;
        vm_object_offset_t      offset;
        register vm_page_t      m;
        vm_prot_t               prot;
        thread_t                thread = current_thread();
        int                     type_of_fault;
        kern_return_t           kr;

        VM_STAT_INCR(faults);

        if (thread != THREAD_NULL && thread->task != TASK_NULL)
          thread->task->faults++;

/*
 *      Recovery actions
 */

#undef  RELEASE_PAGE
#define RELEASE_PAGE(m) {                               \
        PAGE_WAKEUP_DONE(m);                            \
        vm_page_lockspin_queues();                      \
        vm_page_unwire(m);                              \
        vm_page_unlock_queues();                        \
}


#undef  UNLOCK_THINGS
#define UNLOCK_THINGS   {                               \
        vm_object_paging_end(object);                      \
        vm_object_unlock(object);                          \
}

#undef  UNLOCK_AND_DEALLOCATE
#define UNLOCK_AND_DEALLOCATE   {                       \
        UNLOCK_THINGS;                                  \
        vm_object_deallocate(object);                   \
}
/*
 *      Give up and have caller do things the hard way.
 */

#define GIVE_UP {                                       \
        UNLOCK_AND_DEALLOCATE;                          \
        return(KERN_FAILURE);                           \
}


        /*
         *      If this entry is not directly to a vm_object, bail out.
         */
        if (entry->is_sub_map)
                return(KERN_FAILURE);

        /*
         *      Find the backing store object and offset into it.
         */

        object = entry->object.vm_object;
        offset = (va - entry->vme_start) + entry->offset;
        prot = entry->protection;

        /*
         *      Make a reference to this object to prevent its
         *      disposal while we are messing with it.
         */

        vm_object_lock(object);
        vm_object_reference_locked(object);
        vm_object_paging_begin(object);

        /*
         *      INVARIANTS (through entire routine):
         *
         *      1)      At all times, we must either have the object
         *              lock or a busy page in some object to prevent
         *              some other thread from trying to bring in
         *              the same page.
         *
         *      2)      Once we have a busy page, we must remove it from
         *              the pageout queues, so that the pageout daemon
         *              will not grab it away.
         *
         */

        /*
         *      Look for page in top-level object.  If it's not there or
         *      there's something going on, give up.
         * ENCRYPTED SWAP: use the slow fault path, since we'll need to
         * decrypt the page before wiring it down.
         */
        m = vm_page_lookup(object, offset);
        if ((m == VM_PAGE_NULL) || (m->busy) || (m->encrypted) ||
            (m->unusual && ( m->error || m->restart || m->absent))) {

                GIVE_UP;
        }
        ASSERT_PAGE_DECRYPTED(m);

        if (m->fictitious &&
            m->phys_page == vm_page_guard_addr) {
                /*
                 * Guard pages are fictitious pages and are never
                 * entered into a pmap, so let's say it's been wired...
                 */
                kr = KERN_SUCCESS;
                goto done;
        }

        /*
         *      Wire the page down now.  All bail outs beyond this
         *      point must unwire the page.  
         */

        vm_page_lockspin_queues();
        vm_page_wire(m);
        vm_page_unlock_queues();

        /*
         *      Mark page busy for other threads.
         */
        assert(!m->busy);
        m->busy = TRUE;
        assert(!m->absent);

        /*
         *      Give up if the page is being written and there's a copy object
         */
        if ((object->copy != VM_OBJECT_NULL) && (prot & VM_PROT_WRITE)) {
                RELEASE_PAGE(m);
                GIVE_UP;
        }

        /*
         *      Put this page into the physical map.
         */
        type_of_fault = DBG_CACHE_HIT_FAULT;
        kr = vm_fault_enter(m,
                            pmap,
                            pmap_addr,
                            prot,
                            TRUE,
                            FALSE,
                            FALSE,
                            &type_of_fault);

done:
        /*
         *      Unlock everything, and return
         */

        PAGE_WAKEUP_DONE(m);
        UNLOCK_AND_DEALLOCATE;

        return kr;

}

/*
 *      Routine:        vm_fault_copy_cleanup
 *      Purpose:
 *              Release a page used by vm_fault_copy.
 */

void
vm_fault_copy_cleanup(
        vm_page_t       page,
        vm_page_t       top_page)
{
        vm_object_t     object = page->object;

        vm_object_lock(object);
        PAGE_WAKEUP_DONE(page);
        vm_page_lockspin_queues();
        if (!page->active && !page->inactive && !page->throttled)
                vm_page_activate(page);
        vm_page_unlock_queues();
        vm_fault_cleanup(object, top_page);
}

void
vm_fault_copy_dst_cleanup(
        vm_page_t       page)
{
        vm_object_t     object;

        if (page != VM_PAGE_NULL) {
                object = page->object;
                vm_object_lock(object);
                vm_page_lockspin_queues();
                vm_page_unwire(page);
                vm_page_unlock_queues();
                vm_object_paging_end(object);   
                vm_object_unlock(object);
        }
}

/*
 *      Routine:        vm_fault_copy
 *
 *      Purpose:
 *              Copy pages from one virtual memory object to another --
 *              neither the source nor destination pages need be resident.
 *
 *              Before actually copying a page, the version associated with
 *              the destination address map wil be verified.
 *
 *      In/out conditions:
 *              The caller must hold a reference, but not a lock, to
 *              each of the source and destination objects and to the
 *              destination map.
 *
 *      Results:
 *              Returns KERN_SUCCESS if no errors were encountered in
 *              reading or writing the data.  Returns KERN_INTERRUPTED if
 *              the operation was interrupted (only possible if the
 *              "interruptible" argument is asserted).  Other return values
 *              indicate a permanent error in copying the data.
 *
 *              The actual amount of data copied will be returned in the
 *              "copy_size" argument.  In the event that the destination map
 *              verification failed, this amount may be less than the amount
 *              requested.
 */
kern_return_t
vm_fault_copy(
        vm_object_t             src_object,
        vm_object_offset_t      src_offset,
        vm_map_size_t           *copy_size,             /* INOUT */
        vm_object_t             dst_object,
        vm_object_offset_t      dst_offset,
        vm_map_t                dst_map,
        vm_map_version_t         *dst_version,
        int                     interruptible)
{
        vm_page_t               result_page;
        
        vm_page_t               src_page;
        vm_page_t               src_top_page;
        vm_prot_t               src_prot;

        vm_page_t               dst_page;
        vm_page_t               dst_top_page;
        vm_prot_t               dst_prot;

        vm_map_size_t           amount_left;
        vm_object_t             old_copy_object;
        kern_return_t           error = 0;

        vm_map_size_t           part_size;
        struct vm_object_fault_info fault_info_src;
        struct vm_object_fault_info fault_info_dst;

        /*
         * In order not to confuse the clustered pageins, align
         * the different offsets on a page boundary.
         */

#define RETURN(x)                                       \
        MACRO_BEGIN                                     \
        *copy_size -= amount_left;                      \
        MACRO_RETURN(x);                                \
        MACRO_END

        amount_left = *copy_size;

        fault_info_src.interruptible = interruptible;
        fault_info_src.behavior = VM_BEHAVIOR_SEQUENTIAL;
        fault_info_src.user_tag  = 0;
        fault_info_src.lo_offset = vm_object_trunc_page(src_offset);
        fault_info_src.hi_offset = fault_info_src.lo_offset + amount_left;
        fault_info_src.no_cache   = FALSE;

        fault_info_dst.interruptible = interruptible;
        fault_info_dst.behavior = VM_BEHAVIOR_SEQUENTIAL;
        fault_info_dst.user_tag  = 0;
        fault_info_dst.lo_offset = vm_object_trunc_page(dst_offset);
        fault_info_dst.hi_offset = fault_info_dst.lo_offset + amount_left;
        fault_info_dst.no_cache   = FALSE;

        do { /* while (amount_left > 0) */
                /*
                 * There may be a deadlock if both source and destination
                 * pages are the same. To avoid this deadlock, the copy must
                 * start by getting the destination page in order to apply
                 * COW semantics if any.
                 */

        RetryDestinationFault: ;

                dst_prot = VM_PROT_WRITE|VM_PROT_READ;

                vm_object_lock(dst_object);
                vm_object_paging_begin(dst_object);

                fault_info_dst.cluster_size = amount_left;

                XPR(XPR_VM_FAULT,"vm_fault_copy -> vm_fault_page\n",0,0,0,0,0);
                switch (vm_fault_page(dst_object,
                                      vm_object_trunc_page(dst_offset),
                                      VM_PROT_WRITE|VM_PROT_READ,
                                      FALSE,
                                      &dst_prot, &dst_page, &dst_top_page,
                                      (int *)0,
                                      &error,
                                      dst_map->no_zero_fill,
                                      FALSE, &fault_info_dst)) {
                case VM_FAULT_SUCCESS:
                        break;
                case VM_FAULT_RETRY:
                        goto RetryDestinationFault;
                case VM_FAULT_MEMORY_SHORTAGE:
                        if (vm_page_wait(interruptible))
                                goto RetryDestinationFault;
                        /* fall thru */
                case VM_FAULT_INTERRUPTED:
                        RETURN(MACH_SEND_INTERRUPTED);
                case VM_FAULT_MEMORY_ERROR:
                        if (error)
                                return (error);
                        else
                                return(KERN_MEMORY_ERROR);
                }
                assert ((dst_prot & VM_PROT_WRITE) != VM_PROT_NONE);

                old_copy_object = dst_page->object->copy;

                /*
                 * There exists the possiblity that the source and
                 * destination page are the same.  But we can't
                 * easily determine that now.  If they are the
                 * same, the call to vm_fault_page() for the
                 * destination page will deadlock.  To prevent this we
                 * wire the page so we can drop busy without having
                 * the page daemon steal the page.  We clean up the 
                 * top page  but keep the paging reference on the object
                 * holding the dest page so it doesn't go away.
                 */

                vm_page_lockspin_queues();
                vm_page_wire(dst_page);
                vm_page_unlock_queues();
                PAGE_WAKEUP_DONE(dst_page);
                vm_object_unlock(dst_page->object);

                if (dst_top_page != VM_PAGE_NULL) {
                        vm_object_lock(dst_object);
                        VM_PAGE_FREE(dst_top_page);
                        vm_object_paging_end(dst_object);
                        vm_object_unlock(dst_object);
                }

        RetrySourceFault: ;

                if (src_object == VM_OBJECT_NULL) {
                        /*
                         *      No source object.  We will just
                         *      zero-fill the page in dst_object.
                         */
                        src_page = VM_PAGE_NULL;
                        result_page = VM_PAGE_NULL;
                } else {
                        vm_object_lock(src_object);
                        src_page = vm_page_lookup(src_object,
                                                  vm_object_trunc_page(src_offset));
                        if (src_page == dst_page) {
                                src_prot = dst_prot;
                                result_page = VM_PAGE_NULL;
                        } else {
                                src_prot = VM_PROT_READ;
                                vm_object_paging_begin(src_object);

                                fault_info_src.cluster_size = amount_left;

                                XPR(XPR_VM_FAULT,
                                        "vm_fault_copy(2) -> vm_fault_page\n",
                                        0,0,0,0,0);
                                switch (vm_fault_page(
                                                src_object, 
                                                vm_object_trunc_page(src_offset),
                                                VM_PROT_READ, FALSE,
                                                &src_prot, 
                                                &result_page, &src_top_page,
                                                (int *)0, &error, FALSE,
                                                FALSE, &fault_info_src)) {

                                case VM_FAULT_SUCCESS:
                                        break;
                                case VM_FAULT_RETRY:
                                        goto RetrySourceFault;
                                case VM_FAULT_MEMORY_SHORTAGE:
                                        if (vm_page_wait(interruptible))
                                                goto RetrySourceFault;
                                        /* fall thru */
                                case VM_FAULT_INTERRUPTED:
                                        vm_fault_copy_dst_cleanup(dst_page);
                                        RETURN(MACH_SEND_INTERRUPTED);
                                case VM_FAULT_MEMORY_ERROR:
                                        vm_fault_copy_dst_cleanup(dst_page);
                                        if (error)
                                                return (error);
                                        else
                                                return(KERN_MEMORY_ERROR);
                                }


                                assert((src_top_page == VM_PAGE_NULL) ==
                                       (result_page->object == src_object));
                        }
                        assert ((src_prot & VM_PROT_READ) != VM_PROT_NONE);
                        vm_object_unlock(result_page->object);
                }

                if (!vm_map_verify(dst_map, dst_version)) {
                        if (result_page != VM_PAGE_NULL && src_page != dst_page)
                                vm_fault_copy_cleanup(result_page, src_top_page);
                        vm_fault_copy_dst_cleanup(dst_page);
                        break;
                }

                vm_object_lock(dst_page->object);

                if (dst_page->object->copy != old_copy_object) {
                        vm_object_unlock(dst_page->object);
                        vm_map_verify_done(dst_map, dst_version);
                        if (result_page != VM_PAGE_NULL && src_page != dst_page)
                                vm_fault_copy_cleanup(result_page, src_top_page);
                        vm_fault_copy_dst_cleanup(dst_page);
                        break;
                }
                vm_object_unlock(dst_page->object);

                /*
                 *      Copy the page, and note that it is dirty
                 *      immediately.
                 */

                if (!page_aligned(src_offset) ||
                        !page_aligned(dst_offset) ||
                        !page_aligned(amount_left)) {

                        vm_object_offset_t      src_po,
                                                dst_po;

                        src_po = src_offset - vm_object_trunc_page(src_offset);
                        dst_po = dst_offset - vm_object_trunc_page(dst_offset);

                        if (dst_po > src_po) {
                                part_size = PAGE_SIZE - dst_po;
                        } else {
                                part_size = PAGE_SIZE - src_po;
                        }
                        if (part_size > (amount_left)){
                                part_size = amount_left;
                        }

                        if (result_page == VM_PAGE_NULL) {
                                vm_page_part_zero_fill(dst_page,
                                                        dst_po, part_size);
                        } else {
                                vm_page_part_copy(result_page, src_po,
                                        dst_page, dst_po, part_size);
                                if(!dst_page->dirty){
                                        vm_object_lock(dst_object);
                                        dst_page->dirty = TRUE;
                                        vm_object_unlock(dst_page->object);
                                }

                        }
                } else {
                        part_size = PAGE_SIZE;

                        if (result_page == VM_PAGE_NULL)
                                vm_page_zero_fill(dst_page);
                        else{
                                vm_page_copy(result_page, dst_page);
                                if(!dst_page->dirty){
                                        vm_object_lock(dst_object);
                                        dst_page->dirty = TRUE;
                                        vm_object_unlock(dst_page->object);
                                }
                        }

                }

                /*
                 *      Unlock everything, and return
                 */

                vm_map_verify_done(dst_map, dst_version);

                if (result_page != VM_PAGE_NULL && src_page != dst_page)
                        vm_fault_copy_cleanup(result_page, src_top_page);
                vm_fault_copy_dst_cleanup(dst_page);

                amount_left -= part_size;
                src_offset += part_size;
                dst_offset += part_size;
        } while (amount_left > 0);

        RETURN(KERN_SUCCESS);
#undef  RETURN

        /*NOTREACHED*/  
}

#if     VM_FAULT_CLASSIFY
/*
 *      Temporary statistics gathering support.
 */

/*
 *      Statistics arrays:
 */
#define VM_FAULT_TYPES_MAX      5
#define VM_FAULT_LEVEL_MAX      8

int     vm_fault_stats[VM_FAULT_TYPES_MAX][VM_FAULT_LEVEL_MAX];

#define VM_FAULT_TYPE_ZERO_FILL 0
#define VM_FAULT_TYPE_MAP_IN    1
#define VM_FAULT_TYPE_PAGER     2
#define VM_FAULT_TYPE_COPY      3
#define VM_FAULT_TYPE_OTHER     4


void
vm_fault_classify(vm_object_t           object,
                  vm_object_offset_t    offset,
                  vm_prot_t             fault_type)
{
        int             type, level = 0;
        vm_page_t       m;

        while (TRUE) {
                m = vm_page_lookup(object, offset);
                if (m != VM_PAGE_NULL) {                
                        if (m->busy || m->error || m->restart || m->absent) {
                                type = VM_FAULT_TYPE_OTHER;
                                break;
                        }
                        if (((fault_type & VM_PROT_WRITE) == 0) ||
                            ((level == 0) && object->copy == VM_OBJECT_NULL)) {
                                type = VM_FAULT_TYPE_MAP_IN;
                                break;  
                        }
                        type = VM_FAULT_TYPE_COPY;
                        break;
                }
                else {
                        if (object->pager_created) {
                                type = VM_FAULT_TYPE_PAGER;
                                break;
                        }
                        if (object->shadow == VM_OBJECT_NULL) {
                                type = VM_FAULT_TYPE_ZERO_FILL;
                                break;
                        }

                        offset += object->shadow_offset;
                        object = object->shadow;
                        level++;
                        continue;
                }
        }

        if (level > VM_FAULT_LEVEL_MAX)
                level = VM_FAULT_LEVEL_MAX;

        vm_fault_stats[type][level] += 1;

        return;
}

/* cleanup routine to call from debugger */

void
vm_fault_classify_init(void)
{
        int type, level;

        for (type = 0; type < VM_FAULT_TYPES_MAX; type++) {
                for (level = 0; level < VM_FAULT_LEVEL_MAX; level++) {
                        vm_fault_stats[type][level] = 0;
                }
        }

        return;
}
#endif  /* VM_FAULT_CLASSIFY */


extern int cs_validation;

void
vm_page_validate_cs_mapped(
        vm_page_t       page,
        const void      *kaddr)
{
        vm_object_t             object;
        vm_object_offset_t      offset;
        kern_return_t           kr;
        memory_object_t         pager;
        void                    *blobs;
        boolean_t               validated, tainted;

        assert(page->busy);
        vm_object_lock_assert_exclusive(page->object);

        if (!cs_validation) {
                return;
        }

        if (page->wpmapped && !page->cs_tainted) {
                /*
                 * This page was mapped for "write" access sometime in the
                 * past and could still be modifiable in the future.
                 * Consider it tainted.
                 * [ If the page was already found to be "tainted", no
                 * need to re-validate. ]
                 */
                page->cs_validated = TRUE;
                page->cs_tainted = TRUE;
                if (cs_debug) {
                        printf("CODESIGNING: vm_page_validate_cs: "
                               "page %p obj %p off 0x%llx "
                               "was modified\n",
                               page, page->object, page->offset);
                }
                vm_cs_validated_dirtied++;
        }

        if (page->cs_validated) {
                return;
        }

        vm_cs_validates++;

        object = page->object;
        assert(object->code_signed);
        offset = page->offset;

        if (!object->alive || object->terminating || object->pager == NULL) {
                /*
                 * The object is terminating and we don't have its pager
                 * so we can't validate the data...
                 */
                return;
        }
        /*
         * Since we get here to validate a page that was brought in by
         * the pager, we know that this pager is all setup and ready
         * by now.
         */
        assert(!object->internal);
        assert(object->pager != NULL);
        assert(object->pager_ready);

        pager = object->pager;

        kr = vnode_pager_get_object_cs_blobs(pager, &blobs);
        if (kr != KERN_SUCCESS) {
                blobs = NULL;
        }

        /* verify the SHA1 hash for this page */
        validated = cs_validate_page(blobs,
                                     offset + object->paging_offset,
                                     (const void *)kaddr,
                                     &tainted);

        page->cs_validated = validated;
        if (validated) {
                page->cs_tainted = tainted;
        }
}

void
vm_page_validate_cs(
        vm_page_t       page)
{
        vm_object_t             object;
        vm_object_offset_t      offset;
        vm_map_offset_t         koffset;
        vm_map_size_t           ksize;
        vm_offset_t             kaddr;
        kern_return_t           kr;
        boolean_t               busy_page;

        vm_object_lock_assert_held(page->object);

        if (!cs_validation) {
                return;
        }

        if (page->wpmapped && !page->cs_tainted) {
                vm_object_lock_assert_exclusive(page->object);

                /*
                 * This page was mapped for "write" access sometime in the
                 * past and could still be modifiable in the future.
                 * Consider it tainted.
                 * [ If the page was already found to be "tainted", no
                 * need to re-validate. ]
                 */
                page->cs_validated = TRUE;
                page->cs_tainted = TRUE;
                if (cs_debug) {
                        printf("CODESIGNING: vm_page_validate_cs: "
                               "page %p obj %p off 0x%llx "
                               "was modified\n",
                               page, page->object, page->offset);
                }
                vm_cs_validated_dirtied++;
        }

        if (page->cs_validated) {
                return;
        }

        vm_object_lock_assert_exclusive(page->object);

        object = page->object;
        assert(object->code_signed);
        offset = page->offset;

        busy_page = page->busy;
        if (!busy_page) {
                /* keep page busy while we map (and unlock) the VM object */
                page->busy = TRUE;
        }
        
        /*
         * Take a paging reference on the VM object
         * to protect it from collapse or bypass,
         * and keep it from disappearing too.
         */
        vm_object_paging_begin(object);

        /* map the page in the kernel address space */
        koffset = 0;
        ksize = PAGE_SIZE_64;
        kr = vm_paging_map_object(&koffset,
                                  page,
                                  object,
                                  offset,
                                  &ksize,
                                  VM_PROT_READ,
                                  FALSE); /* can't unlock object ! */
        if (kr != KERN_SUCCESS) {
                panic("vm_page_validate_cs: could not map page: 0x%x\n", kr);
        }
        kaddr = CAST_DOWN(vm_offset_t, koffset);

        /* validate the mapped page */
        vm_page_validate_cs_mapped(page, (const void *) kaddr);

        assert(page->busy);
        assert(object == page->object);
        vm_object_lock_assert_exclusive(object);

        if (!busy_page) {
                PAGE_WAKEUP_DONE(page);
        }
        if (koffset != 0) {
                /* unmap the map from the kernel address space */
                vm_paging_unmap_object(object, koffset, koffset + ksize);
                koffset = 0;
                ksize = 0;
                kaddr = 0;
        }
        vm_object_paging_end(object);
}