osfmk/kern/ast.c

   1 /*
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  10  * may not be used to create, or enable the creation or redistribution of,
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  28 /*
  29  * @OSF_COPYRIGHT@
  30  */
  31 /*
  32  * Mach Operating System
  33  * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University
  34  * All Rights Reserved.
  35  *
  36  * Permission to use, copy, modify and distribute this software and its
  37  * documentation is hereby granted, provided that both the copyright
  38  * notice and this permission notice appear in all copies of the
  39  * software, derivative works or modified versions, and any portions
  40  * thereof, and that both notices appear in supporting documentation.
  41  *
  42  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
  43  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
  44  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
  45  *
  46  * Carnegie Mellon requests users of this software to return to
  47  *
  48  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
  49  *  School of Computer Science
  50  *  Carnegie Mellon University
  51  *  Pittsburgh PA 15213-3890
  52  *
  53  * any improvements or extensions that they make and grant Carnegie Mellon
  54  * the rights to redistribute these changes.
  55  */
  56
  57 #include <kern/ast.h>
  58 #include <kern/counters.h>
  59 #include <kern/cpu_quiesce.h>
  60 #include <kern/misc_protos.h>
  61 #include <kern/queue.h>
  62 #include <kern/sched_prim.h>
  63 #include <kern/thread.h>
  64 #include <kern/processor.h>
  65 #include <kern/spl.h>
  66 #include <kern/sfi.h>
  67 #if CONFIG_TELEMETRY
  68 #include <kern/telemetry.h>
  69 #endif
  70 #include <kern/waitq.h>
  71 #include <kern/ledger.h>
  72 #include <kern/machine.h>
  73 #include <kperf/kperf_kpc.h>
  74 #include <mach/policy.h>
  75 #include <security/mac_mach_internal.h> // for MACF AST hook
  76 #include <stdatomic.h>
  77
  78 static void __attribute__((noinline, noreturn, disable_tail_calls))
  79 thread_preempted(__unused void* parameter, __unused wait_result_t result)
  80 {
  81         /*
  82          * We've been scheduled again after a userspace preemption,
  83          * try again to return to userspace.
  84          */
  85         thread_exception_return();
  86 }
  87
  88 /*
  89  * AST_URGENT was detected while in kernel mode
  90  * Called with interrupts disabled, returns the same way
  91  * Must return to caller
  92  */
  93 void
  94 ast_taken_kernel(void)
  95 {
  96         assert(ml_get_interrupts_enabled() == FALSE);
  97
  98         thread_t thread = current_thread();
  99
 100         /* Idle threads handle preemption themselves */
 101         if ((thread->state & TH_IDLE)) {
 102                 ast_off(AST_PREEMPTION);
 103                 return;
 104         }
 105
 106         /*
 107          * It's possible for this to be called after AST_URGENT
 108          * has already been handled, due to races in enable_preemption
 109          */
 110         if (ast_peek(AST_URGENT) != AST_URGENT) {
 111                 return;
 112         }
 113
 114         /*
 115          * Don't preempt if the thread is already preparing to block.
 116          * TODO: the thread can cheese this with clear_wait()
 117          */
 118         if (waitq_wait_possible(thread) == FALSE) {
 119                 /* Consume AST_URGENT or the interrupt will call us again */
 120                 ast_consume(AST_URGENT);
 121                 return;
 122         }
 123
 124         /* TODO: Should we csw_check again to notice if conditions have changed? */
 125
 126         ast_t urgent_reason = ast_consume(AST_PREEMPTION);
 127
 128         assert(urgent_reason & AST_PREEMPT);
 129
 130         counter(c_ast_taken_block++);
 131
 132         thread_block_reason(THREAD_CONTINUE_NULL, NULL, urgent_reason);
 133
 134         assert(ml_get_interrupts_enabled() == FALSE);
 135 }
 136
 137 /*
 138  * An AST flag was set while returning to user mode
 139  * Called with interrupts disabled, returns with interrupts enabled
 140  * May call continuation instead of returning
 141  */
 142 void
 143 ast_taken_user(void)
 144 {
 145         assert(ml_get_interrupts_enabled() == FALSE);
 146
 147         thread_t thread = current_thread();
 148
 149         /* We are about to return to userspace, there must not be a pending wait */
 150         assert(waitq_wait_possible(thread));
 151         assert((thread->state & TH_IDLE) == 0);
 152
 153         /* TODO: Add more 'return to userspace' assertions here */
 154
 155         /*
 156          * If this thread was urgently preempted in userspace,
 157          * take the preemption before processing the ASTs.
 158          * The trap handler will call us again if we have more ASTs, so it's
 159          * safe to block in a continuation here.
 160          */
 161         if (ast_peek(AST_URGENT) == AST_URGENT) {
 162                 ast_t urgent_reason = ast_consume(AST_PREEMPTION);
 163
 164                 assert(urgent_reason & AST_PREEMPT);
 165
 166                 /* TODO: Should we csw_check again to notice if conditions have changed? */
 167
 168                 thread_block_reason(thread_preempted, NULL, urgent_reason);
 169                 /* NOTREACHED */
 170         }
 171
 172         /*
 173          * AST_KEVENT does not send an IPI when setting the ast for a thread running in parallel
 174          * on a different processor. Only the ast bit on the thread will be set.
 175          *
 176          * Force a propagate for concurrent updates without an IPI.
 177          */
 178         ast_propagate(thread);
 179
 180         /*
 181          * Consume all non-preemption processor ASTs matching reasons
 182          * because we're handling them here.
 183          *
 184          * If one of the AST handlers blocks in a continuation,
 185          * we'll reinstate the unserviced thread-level AST flags
 186          * from the thread to the processor on context switch.
 187          * If one of the AST handlers sets another AST,
 188          * the trap handler will call ast_taken_user again.
 189          *
 190          * We expect the AST handlers not to thread_exception_return
 191          * without an ast_propagate or context switch to reinstate
 192          * the per-processor ASTs.
 193          *
 194          * TODO: Why are AST_DTRACE and AST_KPERF not per-thread ASTs?
 195          */
 196         ast_t reasons = ast_consume(AST_PER_THREAD | AST_KPERF | AST_DTRACE);
 197
 198         ml_set_interrupts_enabled(TRUE);
 199
 200 #if CONFIG_DTRACE
 201         if (reasons & AST_DTRACE) {
 202                 dtrace_ast();
 203         }
 204 #endif
 205
 206 #ifdef MACH_BSD
 207         if (reasons & AST_BSD) {
 208                 thread_ast_clear(thread, AST_BSD);
 209                 bsd_ast(thread);
 210         }
 211 #endif
 212
 213 #if CONFIG_MACF
 214         if (reasons & AST_MACF) {
 215                 thread_ast_clear(thread, AST_MACF);
 216                 mac_thread_userret(thread);
 217         }
 218 #endif
 219
 220         if (reasons & AST_APC) {
 221                 thread_ast_clear(thread, AST_APC);
 222                 thread_apc_ast(thread);
 223         }
 224
 225         if (reasons & AST_GUARD) {
 226                 thread_ast_clear(thread, AST_GUARD);
 227                 guard_ast(thread);
 228         }
 229
 230         if (reasons & AST_LEDGER) {
 231                 thread_ast_clear(thread, AST_LEDGER);
 232                 ledger_ast(thread);
 233         }
 234
 235         if (reasons & AST_KPERF) {
 236                 thread_ast_clear(thread, AST_KPERF);
 237                 kperf_kpc_thread_ast(thread);
 238         }
 239
 240         if (reasons & AST_KEVENT) {
 241                 thread_ast_clear(thread, AST_KEVENT);
 242                 uint16_t bits = atomic_exchange(&thread->kevent_ast_bits, 0);
 243                 if (bits) {
 244                         kevent_ast(thread, bits);
 245                 }
 246         }
 247
 248 #if CONFIG_TELEMETRY
 249         if (reasons & AST_TELEMETRY_ALL) {
 250                 ast_t telemetry_reasons = reasons & AST_TELEMETRY_ALL;
 251                 thread_ast_clear(thread, AST_TELEMETRY_ALL);
 252                 telemetry_ast(thread, telemetry_reasons);
 253         }
 254 #endif
 255
 256         spl_t s = splsched();
 257
 258 #if CONFIG_SCHED_SFI
 259         /*
 260          * SFI is currently a per-processor AST, not a per-thread AST
 261          *      TODO: SFI should be a per-thread AST
 262          */
 263         if (ast_consume(AST_SFI) == AST_SFI) {
 264                 sfi_ast(thread);
 265         }
 266 #endif
 267
 268         /* We are about to return to userspace, there must not be a pending wait */
 269         assert(waitq_wait_possible(thread));
 270
 271         /*
 272          * We've handled all per-thread ASTs, time to handle non-urgent preemption.
 273          *
 274          * We delay reading the preemption bits until now in case the thread
 275          * blocks while handling per-thread ASTs.
 276          *
 277          * If one of the AST handlers had managed to set a new AST bit,
 278          * thread_exception_return will call ast_taken again.
 279          */
 280         ast_t preemption_reasons = ast_consume(AST_PREEMPTION);
 281
 282         if (preemption_reasons & AST_PREEMPT) {
 283                 /* Conditions may have changed from when the AST_PREEMPT was originally set, so re-check. */
 284
 285                 thread_lock(thread);
 286                 preemption_reasons = csw_check(thread, current_processor(), (preemption_reasons & AST_QUANTUM));
 287                 thread_unlock(thread);
 288
 289 #if CONFIG_SCHED_SFI
 290                 /* csw_check might tell us that SFI is needed */
 291                 if (preemption_reasons & AST_SFI) {
 292                         sfi_ast(thread);
 293                 }
 294 #endif
 295
 296                 if (preemption_reasons & AST_PREEMPT) {
 297                         counter(c_ast_taken_block++);
 298                         /* switching to a continuation implicitly re-enables interrupts */
 299                         thread_block_reason(thread_preempted, NULL, preemption_reasons);
 300                         /* NOTREACHED */
 301                 }
 302         }
 303
 304         if (ast_consume(AST_UNQUIESCE) == AST_UNQUIESCE) {
 305                 cpu_quiescent_counter_ast();
 306         }
 307
 308         cpu_quiescent_counter_assert_ast();
 309
 310         splx(s);
 311
 312         /*
 313          * Here's a good place to put assertions of things which must be true
 314          * upon return to userspace.
 315          */
 316         assert((thread->sched_flags & TH_SFLAG_WAITQ_PROMOTED) == 0);
 317         assert((thread->sched_flags & TH_SFLAG_RW_PROMOTED) == 0);
 318         assert((thread->sched_flags & TH_SFLAG_EXEC_PROMOTED) == 0);
 319         assert((thread->sched_flags & TH_SFLAG_PROMOTED) == 0);
 320         assert((thread->sched_flags & TH_SFLAG_DEPRESS) == 0);
 321
 322         assert(thread->promotions == 0);
 323         assert(thread->was_promoted_on_wakeup == 0);
 324         assert(thread->waiting_for_mutex == NULL);
 325         assert(thread->rwlock_count == 0);
 326 }
 327
 328 /*
 329  * Set AST flags on current processor
 330  * Called at splsched
 331  */
 332 void
 333 ast_on(ast_t reasons)
 334 {
 335         ast_t *pending_ast = ast_pending();
 336
 337         *pending_ast |= reasons;
 338 }
 339
 340 /*
 341  * Clear AST flags on current processor
 342  * Called at splsched
 343  */
 344 void
 345 ast_off(ast_t reasons)
 346 {
 347         ast_t *pending_ast = ast_pending();
 348
 349         *pending_ast &= ~reasons;
 350 }
 351
 352 /*
 353  * Consume the requested subset of the AST flags set on the processor
 354  * Return the bits that were set
 355  * Called at splsched
 356  */
 357 ast_t
 358 ast_consume(ast_t reasons)
 359 {
 360         ast_t *pending_ast = ast_pending();
 361
 362         reasons &= *pending_ast;
 363         *pending_ast &= ~reasons;
 364
 365         return reasons;
 366 }
 367
 368 /*
 369  * Read the requested subset of the AST flags set on the processor
 370  * Return the bits that were set, don't modify the processor
 371  * Called at splsched
 372  */
 373 ast_t
 374 ast_peek(ast_t reasons)
 375 {
 376         ast_t *pending_ast = ast_pending();
 377
 378         reasons &= *pending_ast;
 379
 380         return reasons;
 381 }
 382
 383 /*
 384  * Re-set current processor's per-thread AST flags to those set on thread
 385  * Called at splsched
 386  */
 387 void
 388 ast_context(thread_t thread)
 389 {
 390         ast_t *pending_ast = ast_pending();
 391
 392         *pending_ast = ((*pending_ast & ~AST_PER_THREAD) | thread->ast);
 393 }
 394
 395 /*
 396  * Propagate ASTs set on a thread to the current processor
 397  * Called at splsched
 398  */
 399 void
 400 ast_propagate(thread_t thread)
 401 {
 402         ast_on(thread->ast);
 403 }
 404
 405 void
 406 ast_dtrace_on(void)
 407 {
 408         ast_on(AST_DTRACE);
 409 }