1/*
2 * Copyright (c) 2000-2017 Apple Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. The rights granted to you under the License
10 * may not be used to create, or enable the creation or redistribution of,
11 * unlawful or unlicensed copies of an Apple operating system, or to
12 * circumvent, violate, or enable the circumvention or violation of, any
13 * terms of an Apple operating system software license agreement.
14 *
15 * Please obtain a copy of the License at
16 * http://www.opensource.apple.com/apsl/ and read it before using this file.
17 *
18 * The Original Code and all software distributed under the License are
19 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
22 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
23 * Please see the License for the specific language governing rights and
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25 *
26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
27 */
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/counter.h>
59#include <kern/misc_protos.h>
60#include <kern/queue.h>
61#include <kern/sched_prim.h>
62#include <kern/thread.h>
63#include <kern/processor.h>
64#include <kern/restartable.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 <kern/kpc.h>
74#include <kperf/kperf.h>
75#include <mach/policy.h>
76#include <security/mac_mach_internal.h> // for MACF AST hook
77#include <stdatomic.h>
78
79#if CONFIG_ARCADE
80#include <kern/arcade.h>
81#endif
82
83static void __attribute__((noinline, noreturn, disable_tail_calls))
84thread_preempted(__unused void* parameter, __unused wait_result_t result)
85{
86 /*
87 * We've been scheduled again after a userspace preemption,
88 * try again to return to userspace.
89 */
90 thread_exception_return();
91}
92
93/*
94 * Create a dedicated frame to clarify that this thread has been preempted
95 * while running in kernel space.
96 */
97static void __attribute__((noinline, disable_tail_calls))
98thread_preempted_in_kernel(ast_t urgent_reason)
99{
100 thread_block_reason(THREAD_CONTINUE_NULL, NULL, reason: urgent_reason);
101
102 assert(ml_get_interrupts_enabled() == FALSE);
103}
104
105/*
106 * AST_URGENT was detected while in kernel mode
107 * Called with interrupts disabled, returns the same way
108 * Must return to caller
109 */
110void
111ast_taken_kernel(void)
112{
113 assert(ml_get_interrupts_enabled() == FALSE);
114
115 thread_t thread = current_thread();
116
117 /* Idle threads handle preemption themselves */
118 if ((thread->state & TH_IDLE)) {
119 ast_off(AST_PREEMPTION);
120 return;
121 }
122
123 /*
124 * It's possible for this to be called after AST_URGENT
125 * has already been handled, due to races in enable_preemption
126 */
127 if (ast_peek(AST_URGENT) != AST_URGENT) {
128 return;
129 }
130
131 /*
132 * Don't preempt if the thread is already preparing to block.
133 * TODO: the thread can cheese this with clear_wait()
134 */
135 if (waitq_wait_possible(thread) == FALSE) {
136 /* Consume AST_URGENT or the interrupt will call us again */
137 ast_consume(AST_URGENT);
138 return;
139 }
140
141 /* TODO: Should we csw_check again to notice if conditions have changed? */
142
143 ast_t urgent_reason = ast_consume(AST_PREEMPTION);
144
145 assert(urgent_reason & AST_PREEMPT);
146
147 /* We've decided to try context switching */
148 thread_preempted_in_kernel(urgent_reason);
149}
150
151/*
152 * An AST flag was set while returning to user mode
153 * Called with interrupts disabled, returns with interrupts enabled
154 * May call continuation instead of returning
155 */
156void
157ast_taken_user(void)
158{
159 assert(ml_get_interrupts_enabled() == FALSE);
160
161 thread_t thread = current_thread();
162 task_t task = get_threadtask(thread);
163
164 /* We are about to return to userspace, there must not be a pending wait */
165 assert(waitq_wait_possible(thread));
166 assert((thread->state & TH_IDLE) == 0);
167
168 /* TODO: Add more 'return to userspace' assertions here */
169
170 /*
171 * If this thread was urgently preempted in userspace,
172 * take the preemption before processing the ASTs.
173 * The trap handler will call us again if we have more ASTs, so it's
174 * safe to block in a continuation here.
175 */
176 if (ast_peek(AST_URGENT) == AST_URGENT) {
177 ast_t urgent_reason = ast_consume(AST_PREEMPTION);
178
179 assert(urgent_reason & AST_PREEMPT);
180
181 /* TODO: Should we csw_check again to notice if conditions have changed? */
182
183 thread_block_reason(continuation: thread_preempted, NULL, reason: urgent_reason);
184 /* NOTREACHED */
185 }
186
187 /*
188 * AST_KEVENT does not send an IPI when setting the ast for a thread running in parallel
189 * on a different processor. Only the ast bit on the thread will be set.
190 *
191 * Force a propagate for concurrent updates without an IPI.
192 */
193 ast_propagate(thread);
194
195 /*
196 * Consume all non-preemption processor ASTs matching reasons
197 * because we're handling them here.
198 *
199 * If one of the AST handlers blocks in a continuation,
200 * we'll reinstate the unserviced thread-level AST flags
201 * from the thread to the processor on context switch.
202 * If one of the AST handlers sets another AST,
203 * the trap handler will call ast_taken_user again.
204 *
205 * We expect the AST handlers not to thread_exception_return
206 * without an ast_propagate or context switch to reinstate
207 * the per-processor ASTs.
208 *
209 * TODO: Why are AST_DTRACE and AST_KPERF not per-thread ASTs?
210 */
211 ast_t reasons = ast_consume(AST_PER_THREAD | AST_KPERF | AST_DTRACE);
212
213 ml_set_interrupts_enabled(TRUE);
214
215#if CONFIG_DTRACE
216 if (reasons & AST_DTRACE) {
217 dtrace_ast();
218 }
219#endif
220
221#ifdef MACH_BSD
222 if (reasons & AST_BSD) {
223 thread_ast_clear(thread, AST_BSD);
224 bsd_ast(thread);
225 }
226#endif
227
228#if CONFIG_MACF
229 if (reasons & AST_MACF) {
230 thread_ast_clear(thread, AST_MACF);
231 mac_thread_userret(thread);
232 }
233#endif
234
235#if CONFIG_ARCADE
236 if (reasons & AST_ARCADE) {
237 thread_ast_clear(thread, AST_ARCADE);
238 arcade_ast(thread);
239 }
240#endif
241
242 if (reasons & AST_APC) {
243 thread_ast_clear(thread, AST_APC);
244 thread_apc_ast(thread);
245 }
246
247 if (reasons & AST_GUARD) {
248 thread_ast_clear(thread, AST_GUARD);
249 guard_ast(thread);
250 }
251
252 if (reasons & AST_LEDGER) {
253 thread_ast_clear(thread, AST_LEDGER);
254 ledger_ast(thread);
255 }
256
257 if (reasons & AST_KPERF) {
258 thread_ast_clear(thread, AST_KPERF);
259#if CONFIG_CPU_COUNTERS
260 kpc_thread_ast_handler(thread);
261#endif /* CONFIG_CPU_COUNTERS */
262 kperf_thread_ast_handler(thread);
263 thread->kperf_ast = 0;
264 }
265
266 if (reasons & AST_RESET_PCS) {
267 thread_ast_clear(thread, AST_RESET_PCS);
268 thread_reset_pcs_ast(task, thread);
269 }
270
271 if (reasons & AST_KEVENT) {
272 thread_ast_clear(thread, AST_KEVENT);
273 uint16_t bits = atomic_exchange(&thread->kevent_ast_bits, 0);
274 if (bits) {
275 kevent_ast(thread, bits);
276 }
277 }
278
279 if (reasons & AST_PROC_RESOURCE) {
280 thread_ast_clear(thread, AST_PROC_RESOURCE);
281 task_port_space_ast(task);
282#if MACH_BSD
283 proc_filedesc_ast(task);
284#endif /* MACH_BSD */
285 }
286
287#if CONFIG_TELEMETRY
288 if (reasons & AST_TELEMETRY_ALL) {
289 ast_t telemetry_reasons = reasons & AST_TELEMETRY_ALL;
290 thread_ast_clear(thread, AST_TELEMETRY_ALL);
291 telemetry_ast(thread, reasons: telemetry_reasons);
292 }
293#endif
294
295#if MACH_ASSERT
296 if (reasons & AST_DEBUG_ASSERT) {
297 thread_ast_clear(thread, AST_DEBUG_ASSERT);
298 thread_debug_return_to_user_ast(thread);
299 }
300#endif
301
302 spl_t s = splsched();
303
304#if CONFIG_SCHED_SFI
305 /*
306 * SFI is currently a per-processor AST, not a per-thread AST
307 * TODO: SFI should be a per-thread AST
308 */
309 if (ast_consume(AST_SFI) == AST_SFI) {
310 sfi_ast(thread);
311 }
312#endif
313
314 /* We are about to return to userspace, there must not be a pending wait */
315 assert(waitq_wait_possible(thread));
316
317 /*
318 * We've handled all per-thread ASTs, time to handle non-urgent preemption.
319 *
320 * We delay reading the preemption bits until now in case the thread
321 * blocks while handling per-thread ASTs.
322 *
323 * If one of the AST handlers had managed to set a new AST bit,
324 * thread_exception_return will call ast_taken again.
325 */
326 ast_t preemption_reasons = ast_consume(AST_PREEMPTION);
327
328 if (preemption_reasons & AST_PREEMPT) {
329 /* Conditions may have changed from when the AST_PREEMPT was originally set, so re-check. */
330
331 thread_lock(thread);
332 preemption_reasons = csw_check(thread, processor: current_processor(), check_reason: (preemption_reasons & AST_QUANTUM));
333 thread_unlock(thread);
334
335#if CONFIG_SCHED_SFI
336 /* csw_check might tell us that SFI is needed */
337 if (preemption_reasons & AST_SFI) {
338 sfi_ast(thread);
339 }
340#endif
341
342 if (preemption_reasons & AST_PREEMPT) {
343 /* switching to a continuation implicitly re-enables interrupts */
344 thread_block_reason(continuation: thread_preempted, NULL, reason: preemption_reasons);
345 /* NOTREACHED */
346 }
347
348 /*
349 * We previously had a pending AST_PREEMPT, but csw_check
350 * decided that it should no longer be set, and to keep
351 * executing the current thread instead.
352 * Clear the pending preemption timer as we no longer
353 * have a pending AST_PREEMPT to time out.
354 *
355 * TODO: just do the thread block if we see AST_PREEMPT
356 * to avoid taking the pset lock twice.
357 * To do that thread block needs to be smarter
358 * about not context switching when it's not necessary
359 * e.g. the first-timeslice check for queue has priority
360 */
361 clear_pending_nonurgent_preemption(processor: current_processor());
362 }
363
364 splx(s);
365
366 /*
367 * Here's a good place to put assertions of things which must be true
368 * upon return to userspace.
369 */
370 assert(thread->kern_promotion_schedpri == 0);
371 if (thread->rwlock_count > 0) {
372 panic("rwlock_count is %d for thread %p, possibly it still holds a rwlock", thread->rwlock_count, thread);
373 }
374 assert(thread->priority_floor_count == 0);
375
376 assert3u(0, ==, thread->sched_flags &
377 (TH_SFLAG_WAITQ_PROMOTED |
378 TH_SFLAG_RW_PROMOTED |
379 TH_SFLAG_EXEC_PROMOTED |
380 TH_SFLAG_FLOOR_PROMOTED |
381 TH_SFLAG_PROMOTED |
382 TH_SFLAG_DEPRESS));
383}
384
385/*
386 * Set AST flags on current processor
387 * Called at splsched
388 */
389void
390ast_on(ast_t reasons)
391{
392 ast_t *pending_ast = ast_pending();
393
394 *pending_ast |= reasons;
395}
396
397/*
398 * Clear AST flags on current processor
399 * Called at splsched
400 */
401void
402ast_off(ast_t reasons)
403{
404 ast_t *pending_ast = ast_pending();
405
406 *pending_ast &= ~reasons;
407}
408
409/*
410 * Consume the requested subset of the AST flags set on the processor
411 * Return the bits that were set
412 * Called at splsched
413 */
414ast_t
415ast_consume(ast_t reasons)
416{
417 ast_t *pending_ast = ast_pending();
418
419 reasons &= *pending_ast;
420 *pending_ast &= ~reasons;
421
422 return reasons;
423}
424
425/*
426 * Read the requested subset of the AST flags set on the processor
427 * Return the bits that were set, don't modify the processor
428 * Called at splsched
429 */
430ast_t
431ast_peek(ast_t reasons)
432{
433 ast_t *pending_ast = ast_pending();
434
435 reasons &= *pending_ast;
436
437 return reasons;
438}
439
440/*
441 * Re-set current processor's per-thread AST flags to those set on thread
442 * Called at splsched
443 */
444void
445ast_context(thread_t thread)
446{
447 ast_t *pending_ast = ast_pending();
448
449 *pending_ast = (*pending_ast & ~AST_PER_THREAD) | thread_ast_get(thread);
450}
451
452/*
453 * Propagate ASTs set on a thread to the current processor
454 * Called at splsched
455 */
456void
457ast_propagate(thread_t thread)
458{
459 ast_on(thread_ast_get(thread));
460}
461
462void
463ast_dtrace_on(void)
464{
465 ast_on(AST_DTRACE);
466}
467