xnu-4903.231.4.tar.gz

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

/*
 * Copyright (c) 2018 Apple Computer, 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@
 */

#include <sys/errno.h>

#include <mach/mach_types.h>
#include <mach/mach_traps.h>
#include <mach/host_priv.h>
#include <mach/kern_return.h>
#include <mach/memory_object_control.h>
#include <mach/memory_object_types.h>
#include <mach/port.h>
#include <mach/policy.h>
#include <mach/upl.h>
#include <mach/thread_act.h>
#include <mach/mach_vm.h>

#include <kern/host.h>
#include <kern/kalloc.h>
#include <kern/queue.h>
#include <kern/thread.h>
#include <kern/ipc_kobject.h>

#include <ipc/ipc_port.h>
#include <ipc/ipc_space.h>

#include <vm/memory_object.h>
#include <vm/vm_kern.h>
#include <vm/vm_fault.h>
#include <vm/vm_map.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pageout.h>
#include <vm/vm_protos.h>
#include <vm/vm_shared_region.h>


/*
 * SHARED REGION MEMORY PAGER
 *
 * This external memory manager (EMM) handles mappings of a dyld shared cache
 * in shared regions, applying any necessary modifications (sliding,
 * pointer signing, ...).
 *
 * It mostly handles page-in requests (from memory_object_data_request()) by
 * getting the original data from its backing VM object, itself backed by
 * the dyld shared cache file, modifying it if needed and providing it to VM.
 *
 * The modified pages will never be dirtied, so the memory manager doesn't
 * need to handle page-out requests (from memory_object_data_return()).  The
 * pages need to be mapped copy-on-write, so that the originals stay clean.
 *
 * We don't expect to have to handle a large number of shared cache files,
 * so the data structures are very simple (simple linked list) for now.
 */

/* forward declarations */
void shared_region_pager_reference(memory_object_t mem_obj);
void shared_region_pager_deallocate(memory_object_t mem_obj);
kern_return_t shared_region_pager_init(memory_object_t mem_obj,
                                       memory_object_control_t control,
                                       memory_object_cluster_size_t pg_size);
kern_return_t shared_region_pager_terminate(memory_object_t mem_obj);
kern_return_t shared_region_pager_data_request(memory_object_t mem_obj,
                                               memory_object_offset_t offset,
                                               memory_object_cluster_size_t length,
                                               vm_prot_t protection_required,
                                               memory_object_fault_info_t fault_info);
kern_return_t shared_region_pager_data_return(memory_object_t mem_obj,
                                              memory_object_offset_t offset,
                                              memory_object_cluster_size_t      data_cnt,
                                              memory_object_offset_t *resid_offset,
                                              int *io_error,
                                              boolean_t dirty,
                                              boolean_t kernel_copy,
                                              int upl_flags);
kern_return_t shared_region_pager_data_initialize(memory_object_t mem_obj,
                                                  memory_object_offset_t offset,
                                                  memory_object_cluster_size_t data_cnt);
kern_return_t shared_region_pager_data_unlock(memory_object_t mem_obj,
                                              memory_object_offset_t offset,
                                              memory_object_size_t size,
                                              vm_prot_t desired_access);
kern_return_t shared_region_pager_synchronize(memory_object_t mem_obj,
                                              memory_object_offset_t offset,
                                              memory_object_size_t length,
                                              vm_sync_t sync_flags);
kern_return_t shared_region_pager_map(memory_object_t mem_obj,
                                      vm_prot_t prot);
kern_return_t shared_region_pager_last_unmap(memory_object_t mem_obj);

/*
 * Vector of VM operations for this EMM.
 * These routines are invoked by VM via the memory_object_*() interfaces.
 */
const struct memory_object_pager_ops shared_region_pager_ops = {
        shared_region_pager_reference,
        shared_region_pager_deallocate,
        shared_region_pager_init,
        shared_region_pager_terminate,
        shared_region_pager_data_request,
        shared_region_pager_data_return,
        shared_region_pager_data_initialize,
        shared_region_pager_data_unlock,
        shared_region_pager_synchronize,
        shared_region_pager_map,
        shared_region_pager_last_unmap,
        NULL, /* data_reclaim */
        "shared_region"
};

/*
 * The "shared_region_pager" describes a memory object backed by
 * the "shared_region" EMM.
 */
typedef struct shared_region_pager {
        /* mandatory generic header */
        struct memory_object sc_pgr_hdr;

        /* pager-specific data */
        queue_chain_t           pager_queue;    /* next & prev pagers */
        unsigned int            ref_count;      /* reference count */
        boolean_t               is_ready;       /* is this pager ready ? */
        boolean_t               is_mapped;      /* is this mem_obj mapped ? */
        vm_object_t             backing_object; /* VM obj for shared cache */
        vm_object_offset_t      backing_offset;
        struct vm_shared_region_slide_info *scp_slide_info;
} *shared_region_pager_t;
#define SHARED_REGION_PAGER_NULL        ((shared_region_pager_t) NULL)

/*
 * List of memory objects managed by this EMM.
 * The list is protected by the "shared_region_pager_lock" lock.
 */
int shared_region_pager_count = 0;              /* number of pagers */
int shared_region_pager_count_mapped = 0;       /* number of unmapped pagers */
queue_head_t shared_region_pager_queue;
decl_lck_mtx_data(,shared_region_pager_lock)

/*
 * Maximum number of unmapped pagers we're willing to keep around.
 */
int shared_region_pager_cache_limit = 0;

/*
 * Statistics & counters.
 */
int shared_region_pager_count_max = 0;
int shared_region_pager_count_unmapped_max = 0;
int shared_region_pager_num_trim_max = 0;
int shared_region_pager_num_trim_total = 0;


lck_grp_t       shared_region_pager_lck_grp;
lck_grp_attr_t  shared_region_pager_lck_grp_attr;
lck_attr_t      shared_region_pager_lck_attr;

uint64_t shared_region_pager_copied = 0;
uint64_t shared_region_pager_slid = 0;
uint64_t shared_region_pager_slid_error = 0;
uint64_t shared_region_pager_reclaimed = 0;

/* internal prototypes */
shared_region_pager_t shared_region_pager_create(
        vm_object_t backing_object,
        vm_object_offset_t backing_offset,
        struct vm_shared_region_slide_info *slide_info);
shared_region_pager_t shared_region_pager_lookup(memory_object_t mem_obj);
void shared_region_pager_dequeue(shared_region_pager_t pager);
void shared_region_pager_deallocate_internal(shared_region_pager_t pager,
                                             boolean_t locked);
void shared_region_pager_terminate_internal(shared_region_pager_t pager);
void shared_region_pager_trim(void);


#if DEBUG
int shared_region_pagerdebug = 0;
#define PAGER_ALL               0xffffffff
#define PAGER_INIT              0x00000001
#define PAGER_PAGEIN            0x00000002

#define PAGER_DEBUG(LEVEL, A)                                           \
        MACRO_BEGIN                                                     \
        if ((shared_region_pagerdebug & (LEVEL)) == (LEVEL)) {          \
                printf A;                                               \
        }                                                               \
        MACRO_END
#else
#define PAGER_DEBUG(LEVEL, A)
#endif


void
shared_region_pager_bootstrap(void)
{
        lck_grp_attr_setdefault(&shared_region_pager_lck_grp_attr);
        lck_grp_init(&shared_region_pager_lck_grp, "shared_region", &shared_region_pager_lck_grp_attr);
        lck_attr_setdefault(&shared_region_pager_lck_attr);
        lck_mtx_init(&shared_region_pager_lock, &shared_region_pager_lck_grp, &shared_region_pager_lck_attr);
        queue_init(&shared_region_pager_queue);
}

/*
 * shared_region_pager_init()
 *
 * Initialize the memory object and makes it ready to be used and mapped.
 */
kern_return_t
shared_region_pager_init(
        memory_object_t         mem_obj,
        memory_object_control_t control,
#if !DEBUG
        __unused
#endif
        memory_object_cluster_size_t pg_size)
{
        shared_region_pager_t   pager;
        kern_return_t           kr;
        memory_object_attr_info_data_t  attributes;

        PAGER_DEBUG(PAGER_ALL,
                    ("shared_region_pager_init: %p, %p, %x\n",
                     mem_obj, control, pg_size));

        if (control == MEMORY_OBJECT_CONTROL_NULL)
                return KERN_INVALID_ARGUMENT;

        pager = shared_region_pager_lookup(mem_obj);

        memory_object_control_reference(control);

        pager->sc_pgr_hdr.mo_control = control;

        attributes.copy_strategy = MEMORY_OBJECT_COPY_DELAY;
        /* attributes.cluster_size = (1 << (CLUSTER_SHIFT + PAGE_SHIFT));*/
        attributes.cluster_size = (1 << (PAGE_SHIFT));
        attributes.may_cache_object = FALSE;
        attributes.temporary = TRUE;

        kr = memory_object_change_attributes(
                                        control,
                                        MEMORY_OBJECT_ATTRIBUTE_INFO,
                                        (memory_object_info_t) &attributes,
                                        MEMORY_OBJECT_ATTR_INFO_COUNT);
        if (kr != KERN_SUCCESS)
                panic("shared_region_pager_init: "
                      "memory_object_change_attributes() failed");

#if CONFIG_SECLUDED_MEMORY
        if (secluded_for_filecache) {
#if 00
                /*
                 * XXX FBDP do we want this in the secluded pool?
                 * Ideally, we'd want the shared region used by Camera to
                 * NOT be in the secluded pool, but all other shared regions
                 * in the secluded pool...
                 */
                memory_object_mark_eligible_for_secluded(control, TRUE);
#endif /* 00 */
        }
#endif /* CONFIG_SECLUDED_MEMORY */

        return KERN_SUCCESS;
}

/*
 * shared_region_data_return()
 *
 * Handles page-out requests from VM.  This should never happen since
 * the pages provided by this EMM are not supposed to be dirty or dirtied
 * and VM should simply discard the contents and reclaim the pages if it
 * needs to.
 */
kern_return_t
shared_region_pager_data_return(
        __unused memory_object_t        mem_obj,
        __unused memory_object_offset_t offset,
        __unused memory_object_cluster_size_t           data_cnt,
        __unused memory_object_offset_t *resid_offset,
        __unused int                    *io_error,
        __unused boolean_t              dirty,
        __unused boolean_t              kernel_copy,
        __unused int                    upl_flags)
{
        panic("shared_region_pager_data_return: should never get called");
        return KERN_FAILURE;
}

kern_return_t
shared_region_pager_data_initialize(
        __unused memory_object_t        mem_obj,
        __unused memory_object_offset_t offset,
        __unused memory_object_cluster_size_t           data_cnt)
{
        panic("shared_region_pager_data_initialize: should never get called");
        return KERN_FAILURE;
}

kern_return_t
shared_region_pager_data_unlock(
        __unused memory_object_t        mem_obj,
        __unused memory_object_offset_t offset,
        __unused memory_object_size_t           size,
        __unused vm_prot_t              desired_access)
{
        return KERN_FAILURE;
}

/*
 * shared_region_pager_data_request()
 *
 * Handles page-in requests from VM.
 */
int shared_region_pager_data_request_debug = 0;
kern_return_t
shared_region_pager_data_request(
        memory_object_t         mem_obj,
        memory_object_offset_t  offset,
        memory_object_cluster_size_t            length,
#if !DEBUG
        __unused
#endif
        vm_prot_t               protection_required,
        memory_object_fault_info_t mo_fault_info)
{
        shared_region_pager_t   pager;
        memory_object_control_t mo_control;
        upl_t                   upl;
        int                     upl_flags;
        upl_size_t              upl_size;
        upl_page_info_t         *upl_pl;
        unsigned int            pl_count;
        vm_object_t             src_top_object, src_page_object, dst_object;
        kern_return_t           kr, retval;
        vm_offset_t             src_vaddr, dst_vaddr;
        vm_offset_t             cur_offset;
        vm_offset_t             offset_in_page;
        kern_return_t           error_code;
        vm_prot_t               prot;
        vm_page_t               src_page, top_page;
        int                     interruptible;
        struct vm_object_fault_info     fault_info;
        mach_vm_offset_t        slide_start_address;

        PAGER_DEBUG(PAGER_ALL, ("shared_region_pager_data_request: %p, %llx, %x, %x\n", mem_obj, offset, length, protection_required));

        retval = KERN_SUCCESS;
        src_top_object = VM_OBJECT_NULL;
        src_page_object = VM_OBJECT_NULL;
        upl = NULL;
        upl_pl = NULL;
        fault_info = *((struct vm_object_fault_info *)(uintptr_t)mo_fault_info);
        fault_info.stealth = TRUE;
        fault_info.io_sync = FALSE;
        fault_info.mark_zf_absent = FALSE;
        fault_info.batch_pmap_op = FALSE;
        interruptible = fault_info.interruptible;

        pager = shared_region_pager_lookup(mem_obj);
        assert(pager->is_ready);
        assert(pager->ref_count > 1); /* pager is alive and mapped */

        PAGER_DEBUG(PAGER_PAGEIN, ("shared_region_pager_data_request: %p, %llx, %x, %x, pager %p\n", mem_obj, offset, length, protection_required, pager));

        /*
         * Gather in a UPL all the VM pages requested by VM.
         */
        mo_control = pager->sc_pgr_hdr.mo_control;

        upl_size = length;
        upl_flags =
                UPL_RET_ONLY_ABSENT |
                UPL_SET_LITE |
                UPL_NO_SYNC |
                UPL_CLEAN_IN_PLACE |    /* triggers UPL_CLEAR_DIRTY */
                UPL_SET_INTERNAL;
        pl_count = 0;
        kr = memory_object_upl_request(mo_control,
                                       offset, upl_size,
                                       &upl, NULL, NULL, upl_flags, VM_KERN_MEMORY_SECURITY);
        if (kr != KERN_SUCCESS) {
                retval = kr;
                goto done;
        }
        dst_object = mo_control->moc_object;
        assert(dst_object != VM_OBJECT_NULL);

        /*
         * We'll map the original data in the kernel address space from the
         * backing VM object (itself backed by the shared cache file via
         * the vnode pager).
         */
        src_top_object = pager->backing_object;
        assert(src_top_object != VM_OBJECT_NULL);
        vm_object_reference(src_top_object); /* keep the source object alive */

        slide_start_address = pager->scp_slide_info->slid_address;

        fault_info.lo_offset += pager->backing_offset;
        fault_info.hi_offset += pager->backing_offset;

        /*
         * Fill in the contents of the pages requested by VM.
         */
        upl_pl = UPL_GET_INTERNAL_PAGE_LIST(upl);
        pl_count = length / PAGE_SIZE;
        for (cur_offset = 0;
             retval == KERN_SUCCESS && cur_offset < length;
             cur_offset += PAGE_SIZE) {
                ppnum_t dst_pnum;

                if (!upl_page_present(upl_pl, (int)(cur_offset / PAGE_SIZE))) {
                        /* this page is not in the UPL: skip it */
                        continue;
                }

                /*
                 * Map the source (dyld shared cache) page in the kernel's
                 * virtual address space.
                 * We already hold a reference on the src_top_object.
                 */
        retry_src_fault:
                vm_object_lock(src_top_object);
                vm_object_paging_begin(src_top_object);
                error_code = 0;
                prot = VM_PROT_READ;
                src_page = VM_PAGE_NULL;
                kr = vm_fault_page(src_top_object,
                                   pager->backing_offset + offset + cur_offset,
                                   VM_PROT_READ,
                                   FALSE,
                                   FALSE, /* src_page not looked up */
                                   &prot,
                                   &src_page,
                                   &top_page,
                                   NULL,
                                   &error_code,
                                   FALSE,
                                   FALSE,
                                   &fault_info);
                switch (kr) {
                case VM_FAULT_SUCCESS:
                        break;
                case VM_FAULT_RETRY:
                        goto retry_src_fault;
                case VM_FAULT_MEMORY_SHORTAGE:
                        if (vm_page_wait(interruptible)) {
                                goto retry_src_fault;
                        }
                        /* fall thru */
                case VM_FAULT_INTERRUPTED:
                        retval = MACH_SEND_INTERRUPTED;
                        goto done;
                case VM_FAULT_SUCCESS_NO_VM_PAGE:
                        /* success but no VM page: fail */
                        vm_object_paging_end(src_top_object);
                        vm_object_unlock(src_top_object);
                        /*FALLTHROUGH*/
                case VM_FAULT_MEMORY_ERROR:
                        /* the page is not there ! */
                        if (error_code) {
                                retval = error_code;
                        } else {
                                retval = KERN_MEMORY_ERROR;
                        }
                        goto done;
                default:
                        panic("shared_region_pager_data_request: "
                              "vm_fault_page() unexpected error 0x%x\n",
                              kr);
                }
                assert(src_page != VM_PAGE_NULL);
                assert(src_page->vmp_busy);

                if (src_page->vmp_q_state != VM_PAGE_ON_SPECULATIVE_Q) {
                        vm_page_lockspin_queues();
                        if (src_page->vmp_q_state != VM_PAGE_ON_SPECULATIVE_Q) {
                                vm_page_speculate(src_page, FALSE);
                        }
                        vm_page_unlock_queues();
                }

                /*
                 * Establish pointers to the source
                 * and destination physical pages.
                 */
                dst_pnum = (ppnum_t)
                        upl_phys_page(upl_pl, (int)(cur_offset / PAGE_SIZE));
                assert(dst_pnum != 0);
#if __x86_64__
                src_vaddr = (vm_map_offset_t)
                        PHYSMAP_PTOV((pmap_paddr_t)VM_PAGE_GET_PHYS_PAGE(src_page)
                                     << PAGE_SHIFT);
                dst_vaddr = (vm_map_offset_t)
                        PHYSMAP_PTOV((pmap_paddr_t)dst_pnum << PAGE_SHIFT);

#elif __arm__ || __arm64__
                src_vaddr = (vm_map_offset_t)
                        phystokv((pmap_paddr_t)VM_PAGE_GET_PHYS_PAGE(src_page)
                                 << PAGE_SHIFT);
                dst_vaddr = (vm_map_offset_t)
                        phystokv((pmap_paddr_t)dst_pnum << PAGE_SHIFT);
#else
#error "vm_paging_map_object: no 1-to-1 kernel mapping of physical memory..."
                src_vaddr = 0;
                dst_vaddr = 0;
#endif
                src_page_object = VM_PAGE_OBJECT(src_page);

                /*
                 * Validate the original page...
                 */
                if (src_page_object->code_signed) {
                        vm_page_validate_cs_mapped(
                                src_page,
                                (const void *) src_vaddr);
                }
                /*
                 * ... and transfer the results to the destination page.
                 */
                UPL_SET_CS_VALIDATED(upl_pl, cur_offset / PAGE_SIZE,
                                     src_page->vmp_cs_validated);
                UPL_SET_CS_TAINTED(upl_pl, cur_offset / PAGE_SIZE,
                                   src_page->vmp_cs_tainted);
                UPL_SET_CS_NX(upl_pl, cur_offset / PAGE_SIZE,
                                   src_page->vmp_cs_nx);

                /*
                 * The page provider might access a mapped file, so let's
                 * release the object lock for the source page to avoid a
                 * potential deadlock.
                 * The source page is kept busy and we have a
                 * "paging_in_progress" reference on its object, so it's safe
                 * to unlock the object here.
                 */
                assert(src_page->vmp_busy);
                assert(src_page_object->paging_in_progress > 0);
                vm_object_unlock(src_page_object);

                /*
                 * Process the original contents of the source page
                 * into the destination page.
                 */
                for (offset_in_page = 0;
                     offset_in_page < PAGE_SIZE;
                     offset_in_page += PAGE_SIZE_FOR_SR_SLIDE) {
                        vm_object_offset_t chunk_offset;
                        vm_object_offset_t offset_in_backing_object;
                        vm_object_offset_t offset_in_sliding_range;

                        chunk_offset = offset + cur_offset + offset_in_page;

                        bcopy((const char *)(src_vaddr +
                                             offset_in_page),
                              (char *)(dst_vaddr + offset_in_page),
                              PAGE_SIZE_FOR_SR_SLIDE);

                        offset_in_backing_object = (chunk_offset +
                                                    pager->backing_offset);
                        if ((offset_in_backing_object < pager->scp_slide_info->start) ||
                            (offset_in_backing_object >= pager->scp_slide_info->end)) {
                                /* chunk is outside of sliding range: done */
                                shared_region_pager_copied++;
                                continue;
                        }

                        offset_in_sliding_range =
                                (offset_in_backing_object -
                                 pager->scp_slide_info->start);
                        kr = vm_shared_region_slide_page(
                                pager->scp_slide_info,
                                dst_vaddr + offset_in_page,
                                (mach_vm_offset_t) (offset_in_sliding_range +
                                                    slide_start_address),
                                (uint32_t) (offset_in_sliding_range /
                                            PAGE_SIZE_FOR_SR_SLIDE));
                        if (shared_region_pager_data_request_debug) {
                                printf("shared_region_data_request"
                                       "(%p,0x%llx+0x%llx+0x%04llx): 0x%llx "
                                       "in sliding range [0x%llx:0x%llx]: "
                                       "SLIDE offset 0x%llx="
                                       "(0x%llx+0x%llx+0x%llx+0x%04llx)"
                                       "[0x%016llx 0x%016llx] "
                                       "code_signed=%d "
                                       "cs_validated=%d "
                                       "cs_tainted=%d "
                                       "cs_nx=%d "
                                       "kr=0x%x\n",
                                       pager,
                                       offset,
                                       (uint64_t) cur_offset,
                                       (uint64_t) offset_in_page,
                                       chunk_offset,
                                       pager->scp_slide_info->start,
                                       pager->scp_slide_info->end,
                                       (pager->backing_offset +
                                        offset +
                                        cur_offset +
                                        offset_in_page),
                                       pager->backing_offset,
                                       offset,
                                       (uint64_t) cur_offset,
                                       (uint64_t) offset_in_page,
                                       *(uint64_t *)(dst_vaddr+offset_in_page),
                                       *(uint64_t *)(dst_vaddr+offset_in_page+8),
                                       src_page_object->code_signed,
                                       src_page->vmp_cs_validated,
                                       src_page->vmp_cs_tainted,
                                       src_page->vmp_cs_nx,
                                       kr);
                        }
                        if (kr != KERN_SUCCESS) {
                                shared_region_pager_slid_error++;
                                break;
                        }
                        shared_region_pager_slid++;
                }

                assert(VM_PAGE_OBJECT(src_page) == src_page_object);
                assert(src_page->vmp_busy);
                assert(src_page_object->paging_in_progress > 0);
                vm_object_lock(src_page_object);

                /*
                 * Cleanup the result of vm_fault_page() of the source page.
                 */
                PAGE_WAKEUP_DONE(src_page);
                src_page = VM_PAGE_NULL;
                vm_object_paging_end(src_page_object);
                vm_object_unlock(src_page_object);

                if (top_page != VM_PAGE_NULL) {
                        assert(VM_PAGE_OBJECT(top_page) == src_top_object);
                        vm_object_lock(src_top_object);
                        VM_PAGE_FREE(top_page);
                        vm_object_paging_end(src_top_object);
                        vm_object_unlock(src_top_object);
                }
        }

done:
        if (upl != NULL) {
                /* clean up the UPL */

                /*
                 * The pages are currently dirty because we've just been
                 * writing on them, but as far as we're concerned, they're
                 * clean since they contain their "original" contents as
                 * provided by us, the pager.
                 * Tell the UPL to mark them "clean".
                 */
                upl_clear_dirty(upl, TRUE);

                /* abort or commit the UPL */
                if (retval != KERN_SUCCESS) {
                        upl_abort(upl, 0);
                } else {
                        boolean_t empty;
                        upl_commit_range(upl, 0, upl->size,
                                         UPL_COMMIT_CS_VALIDATED | UPL_COMMIT_WRITTEN_BY_KERNEL,
                                         upl_pl, pl_count, &empty);
                }

                /* and deallocate the UPL */
                upl_deallocate(upl);
                upl = NULL;
        }
        if (src_top_object != VM_OBJECT_NULL) {
                vm_object_deallocate(src_top_object);
        }
        return retval;
}

/*
 * shared_region_pager_reference()
 *
 * Get a reference on this memory object.
 * For external usage only.  Assumes that the initial reference count is not 0,
 * i.e one should not "revive" a dead pager this way.
 */
void
shared_region_pager_reference(
        memory_object_t         mem_obj)
{
        shared_region_pager_t   pager;

        pager = shared_region_pager_lookup(mem_obj);

        lck_mtx_lock(&shared_region_pager_lock);
        assert(pager->ref_count > 0);
        pager->ref_count++;
        lck_mtx_unlock(&shared_region_pager_lock);
}


/*
 * shared_region_pager_dequeue:
 *
 * Removes a pager from the list of pagers.
 *
 * The caller must hold "shared_region_pager_lock".
 */
void
shared_region_pager_dequeue(
        shared_region_pager_t pager)
{
        assert(!pager->is_mapped);

        queue_remove(&shared_region_pager_queue,
                     pager,
                     shared_region_pager_t,
                     pager_queue);
        pager->pager_queue.next = NULL;
        pager->pager_queue.prev = NULL;

        shared_region_pager_count--;
}

/*
 * shared_region_pager_terminate_internal:
 *
 * Trigger the asynchronous termination of the memory object associated
 * with this pager.
 * When the memory object is terminated, there will be one more call
 * to memory_object_deallocate() (i.e. shared_region_pager_deallocate())
 * to finish the clean up.
 *
 * "shared_region_pager_lock" should not be held by the caller.
 * We don't need the lock because the pager has already been removed from
 * the pagers' list and is now ours exclusively.
 */
void
shared_region_pager_terminate_internal(
        shared_region_pager_t pager)
{
        assert(pager->is_ready);
        assert(!pager->is_mapped);

        if (pager->backing_object != VM_OBJECT_NULL) {
                vm_object_deallocate(pager->backing_object);
                pager->backing_object = VM_OBJECT_NULL;
        }
        /* trigger the destruction of the memory object */
        memory_object_destroy(pager->sc_pgr_hdr.mo_control, 0);
}

/*
 * shared_region_pager_deallocate_internal()
 *
 * Release a reference on this pager and free it when the last
 * reference goes away.
 * Can be called with shared_region_pager_lock held or not but always returns
 * with it unlocked.
 */
void
shared_region_pager_deallocate_internal(
        shared_region_pager_t   pager,
        boolean_t               locked)
{
        boolean_t       needs_trimming;
        int             count_unmapped;

        if (! locked) {
                lck_mtx_lock(&shared_region_pager_lock);
        }

        count_unmapped = (shared_region_pager_count -
                          shared_region_pager_count_mapped);
        if (count_unmapped > shared_region_pager_cache_limit) {
                /* we have too many unmapped pagers:  trim some */
                needs_trimming = TRUE;
        } else {
                needs_trimming = FALSE;
        }

        /* drop a reference on this pager */
        pager->ref_count--;

        if (pager->ref_count == 1) {
                /*
                 * Only the "named" reference is left, which means that
                 * no one is really holding on to this pager anymore.
                 * Terminate it.
                 */
                shared_region_pager_dequeue(pager);
                /* the pager is all ours: no need for the lock now */
                lck_mtx_unlock(&shared_region_pager_lock);
                shared_region_pager_terminate_internal(pager);
        } else if (pager->ref_count == 0) {
                /*
                 * Dropped the existence reference;  the memory object has
                 * been terminated.  Do some final cleanup and release the
                 * pager structure.
                 */
                lck_mtx_unlock(&shared_region_pager_lock);
                if (pager->sc_pgr_hdr.mo_control != MEMORY_OBJECT_CONTROL_NULL) {
                        memory_object_control_deallocate(pager->sc_pgr_hdr.mo_control);
                        pager->sc_pgr_hdr.mo_control = MEMORY_OBJECT_CONTROL_NULL;
                }
                kfree(pager, sizeof (*pager));
                pager = SHARED_REGION_PAGER_NULL;
        } else {
                /* there are still plenty of references:  keep going... */
                lck_mtx_unlock(&shared_region_pager_lock);
        }

        if (needs_trimming) {
                shared_region_pager_trim();
        }
        /* caution: lock is not held on return... */
}

/*
 * shared_region_pager_deallocate()
 *
 * Release a reference on this pager and free it when the last
 * reference goes away.
 */
void
shared_region_pager_deallocate(
        memory_object_t         mem_obj)
{
        shared_region_pager_t   pager;

        PAGER_DEBUG(PAGER_ALL, ("shared_region_pager_deallocate: %p\n", mem_obj));
        pager = shared_region_pager_lookup(mem_obj);
        shared_region_pager_deallocate_internal(pager, FALSE);
}

/*
 *
 */
kern_return_t
shared_region_pager_terminate(
#if !DEBUG
        __unused
#endif
        memory_object_t mem_obj)
{
        PAGER_DEBUG(PAGER_ALL, ("shared_region_pager_terminate: %p\n", mem_obj));

        return KERN_SUCCESS;
}

/*
 *
 */
kern_return_t
shared_region_pager_synchronize(
        __unused memory_object_t                mem_obj,
        __unused memory_object_offset_t offset,
        __unused memory_object_size_t           length,
        __unused vm_sync_t              sync_flags)
{
        panic("shared_region_pager_synchronize: memory_object_synchronize no longer supported\n");
        return KERN_FAILURE;
}

/*
 * shared_region_pager_map()
 *
 * This allows VM to let us, the EMM, know that this memory object
 * is currently mapped one or more times.  This is called by VM each time
 * the memory object gets mapped and we take one extra reference on the
 * memory object to account for all its mappings.
 */
kern_return_t
shared_region_pager_map(
        memory_object_t         mem_obj,
        __unused vm_prot_t      prot)
{
        shared_region_pager_t   pager;

        PAGER_DEBUG(PAGER_ALL, ("shared_region_pager_map: %p\n", mem_obj));

        pager = shared_region_pager_lookup(mem_obj);

        lck_mtx_lock(&shared_region_pager_lock);
        assert(pager->is_ready);
        assert(pager->ref_count > 0); /* pager is alive */
        if (pager->is_mapped == FALSE) {
                /*
                 * First mapping of this pager:  take an extra reference
                 * that will remain until all the mappings of this pager
                 * are removed.
                 */
                pager->is_mapped = TRUE;
                pager->ref_count++;
                shared_region_pager_count_mapped++;
        }
        lck_mtx_unlock(&shared_region_pager_lock);

        return KERN_SUCCESS;
}

/*
 * shared_region_pager_last_unmap()
 *
 * This is called by VM when this memory object is no longer mapped anywhere.
 */
kern_return_t
shared_region_pager_last_unmap(
        memory_object_t         mem_obj)
{
        shared_region_pager_t   pager;
        int                     count_unmapped;

        PAGER_DEBUG(PAGER_ALL,
                    ("shared_region_pager_last_unmap: %p\n", mem_obj));

        pager = shared_region_pager_lookup(mem_obj);

        lck_mtx_lock(&shared_region_pager_lock);
        if (pager->is_mapped) {
                /*
                 * All the mappings are gone, so let go of the one extra
                 * reference that represents all the mappings of this pager.
                 */
                shared_region_pager_count_mapped--;
                count_unmapped = (shared_region_pager_count -
                                  shared_region_pager_count_mapped);
                if (count_unmapped > shared_region_pager_count_unmapped_max) {
                        shared_region_pager_count_unmapped_max = count_unmapped;
                }
                pager->is_mapped = FALSE;
                shared_region_pager_deallocate_internal(pager, TRUE);
                /* caution: deallocate_internal() released the lock ! */
        } else {
                lck_mtx_unlock(&shared_region_pager_lock);
        }

        return KERN_SUCCESS;
}


/*
 *
 */
shared_region_pager_t
shared_region_pager_lookup(
        memory_object_t  mem_obj)
{
        shared_region_pager_t   pager;

        assert(mem_obj->mo_pager_ops == &shared_region_pager_ops);
        pager = (shared_region_pager_t)(uintptr_t) mem_obj;
        assert(pager->ref_count > 0);
        return pager;
}

shared_region_pager_t
shared_region_pager_create(
        vm_object_t             backing_object,
        vm_object_offset_t      backing_offset,
        struct vm_shared_region_slide_info *slide_info)
{
        shared_region_pager_t   pager;
        memory_object_control_t control;
        kern_return_t           kr;

        pager = (shared_region_pager_t) kalloc(sizeof (*pager));
        if (pager == SHARED_REGION_PAGER_NULL) {
                return SHARED_REGION_PAGER_NULL;
        }

        /*
         * The vm_map call takes both named entry ports and raw memory
         * objects in the same parameter.  We need to make sure that
         * vm_map does not see this object as a named entry port.  So,
         * we reserve the first word in the object for a fake ip_kotype
         * setting - that will tell vm_map to use it as a memory object.
         */
        pager->sc_pgr_hdr.mo_ikot = IKOT_MEMORY_OBJECT;
        pager->sc_pgr_hdr.mo_pager_ops = &shared_region_pager_ops;
        pager->sc_pgr_hdr.mo_control = MEMORY_OBJECT_CONTROL_NULL;

        pager->is_ready = FALSE;/* not ready until it has a "name" */
        pager->ref_count = 1;   /* existence reference (for the cache) */
        pager->ref_count++;     /* for the caller */
        pager->is_mapped = FALSE;
        pager->backing_object = backing_object;
        pager->backing_offset = backing_offset;
        pager->scp_slide_info = slide_info;

        vm_object_reference(backing_object);

        lck_mtx_lock(&shared_region_pager_lock);
        /* enter new pager at the head of our list of pagers */
        queue_enter_first(&shared_region_pager_queue,
                          pager,
                          shared_region_pager_t,
                          pager_queue);
        shared_region_pager_count++;
        if (shared_region_pager_count > shared_region_pager_count_max) {
                shared_region_pager_count_max = shared_region_pager_count;
        }
        lck_mtx_unlock(&shared_region_pager_lock);

        kr = memory_object_create_named((memory_object_t) pager,
                                        0,
                                        &control);
        assert(kr == KERN_SUCCESS);

        lck_mtx_lock(&shared_region_pager_lock);
        /* the new pager is now ready to be used */
        pager->is_ready = TRUE;
        lck_mtx_unlock(&shared_region_pager_lock);

        /* wakeup anyone waiting for this pager to be ready */
        thread_wakeup(&pager->is_ready);

        return pager;
}

/*
 * shared_region_pager_setup()
 *
 * Provide the caller with a memory object backed by the provided
 * "backing_object" VM object.
 */
memory_object_t
shared_region_pager_setup(
        vm_object_t             backing_object,
        vm_object_offset_t      backing_offset,
        struct vm_shared_region_slide_info *slide_info)
{
        shared_region_pager_t   pager;

        /* create new pager */
        pager = shared_region_pager_create(
                backing_object,
                backing_offset,
                slide_info);
        if (pager == SHARED_REGION_PAGER_NULL) {
                /* could not create a new pager */
                return MEMORY_OBJECT_NULL;
        }

        lck_mtx_lock(&shared_region_pager_lock);
        while (!pager->is_ready) {
                lck_mtx_sleep(&shared_region_pager_lock,
                        LCK_SLEEP_DEFAULT,
                        &pager->is_ready,
                        THREAD_UNINT);
        }
        lck_mtx_unlock(&shared_region_pager_lock);

        return (memory_object_t) pager;
}

void
shared_region_pager_trim(void)
{
        shared_region_pager_t   pager, prev_pager;
        queue_head_t            trim_queue;
        int                     num_trim;
        int                     count_unmapped;

        lck_mtx_lock(&shared_region_pager_lock);

        /*
         * We have too many pagers, try and trim some unused ones,
         * starting with the oldest pager at the end of the queue.
         */
        queue_init(&trim_queue);
        num_trim = 0;

        for (pager = (shared_region_pager_t)
                     queue_last(&shared_region_pager_queue);
             !queue_end(&shared_region_pager_queue,
                        (queue_entry_t) pager);
             pager = prev_pager) {
                /* get prev elt before we dequeue */
                prev_pager = (shared_region_pager_t)
                        queue_prev(&pager->pager_queue);

                if (pager->ref_count == 2 &&
                    pager->is_ready &&
                    !pager->is_mapped) {
                        /* this pager can be trimmed */
                        num_trim++;
                        /* remove this pager from the main list ... */
                        shared_region_pager_dequeue(pager);
                        /* ... and add it to our trim queue */
                        queue_enter_first(&trim_queue,
                                          pager,
                                          shared_region_pager_t,
                                          pager_queue);

                        count_unmapped = (shared_region_pager_count -
                                          shared_region_pager_count_mapped);
                        if (count_unmapped <= shared_region_pager_cache_limit) {
                                /* we have enough pagers to trim */
                                break;
                        }
                }
        }
        if (num_trim > shared_region_pager_num_trim_max) {
                shared_region_pager_num_trim_max = num_trim;
        }
        shared_region_pager_num_trim_total += num_trim;

        lck_mtx_unlock(&shared_region_pager_lock);

        /* terminate the trimmed pagers */
        while (!queue_empty(&trim_queue)) {
                queue_remove_first(&trim_queue,
                                   pager,
                                   shared_region_pager_t,
                                   pager_queue);
                pager->pager_queue.next = NULL;
                pager->pager_queue.prev = NULL;
                assert(pager->ref_count == 2);
                /*
                 * We can't call deallocate_internal() because the pager
                 * has already been dequeued, but we still need to remove
                 * a reference.
                 */
                pager->ref_count--;
                shared_region_pager_terminate_internal(pager);
        }
}