1/* CPU control.
2 * (C) 2001, 2002, 2003, 2004 Rusty Russell
3 *
4 * This code is licenced under the GPL.
5 */
6#include <linux/sched/mm.h>
7#include <linux/proc_fs.h>
8#include <linux/smp.h>
9#include <linux/init.h>
10#include <linux/notifier.h>
11#include <linux/sched/signal.h>
12#include <linux/sched/hotplug.h>
13#include <linux/sched/isolation.h>
14#include <linux/sched/task.h>
15#include <linux/sched/smt.h>
16#include <linux/unistd.h>
17#include <linux/cpu.h>
18#include <linux/oom.h>
19#include <linux/rcupdate.h>
20#include <linux/delay.h>
21#include <linux/export.h>
22#include <linux/bug.h>
23#include <linux/kthread.h>
24#include <linux/stop_machine.h>
25#include <linux/mutex.h>
26#include <linux/gfp.h>
27#include <linux/suspend.h>
28#include <linux/lockdep.h>
29#include <linux/tick.h>
30#include <linux/irq.h>
31#include <linux/nmi.h>
32#include <linux/smpboot.h>
33#include <linux/relay.h>
34#include <linux/slab.h>
35#include <linux/scs.h>
36#include <linux/percpu-rwsem.h>
37#include <linux/cpuset.h>
38#include <linux/random.h>
39#include <linux/cc_platform.h>
40#include <linux/parser.h>
41
42#include <trace/events/power.h>
43#define CREATE_TRACE_POINTS
44#include <trace/events/cpuhp.h>
45
46#include "smpboot.h"
47
48/**
49 * struct cpuhp_cpu_state - Per cpu hotplug state storage
50 * @state: The current cpu state
51 * @target: The target state
52 * @fail: Current CPU hotplug callback state
53 * @thread: Pointer to the hotplug thread
54 * @should_run: Thread should execute
55 * @rollback: Perform a rollback
56 * @single: Single callback invocation
57 * @bringup: Single callback bringup or teardown selector
58 * @node: Remote CPU node; for multi-instance, do a
59 * single entry callback for install/remove
60 * @last: For multi-instance rollback, remember how far we got
61 * @cb_state: The state for a single callback (install/uninstall)
62 * @result: Result of the operation
63 * @ap_sync_state: State for AP synchronization
64 * @done_up: Signal completion to the issuer of the task for cpu-up
65 * @done_down: Signal completion to the issuer of the task for cpu-down
66 */
67struct cpuhp_cpu_state {
68 enum cpuhp_state state;
69 enum cpuhp_state target;
70 enum cpuhp_state fail;
71#ifdef CONFIG_SMP
72 struct task_struct *thread;
73 bool should_run;
74 bool rollback;
75 bool single;
76 bool bringup;
77 struct hlist_node *node;
78 struct hlist_node *last;
79 enum cpuhp_state cb_state;
80 int result;
81 atomic_t ap_sync_state;
82 struct completion done_up;
83 struct completion done_down;
84#endif
85};
86
87static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {
88 .fail = CPUHP_INVALID,
89};
90
91#ifdef CONFIG_SMP
92cpumask_t cpus_booted_once_mask;
93#endif
94
95#if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
96static struct lockdep_map cpuhp_state_up_map =
97 STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_map);
98static struct lockdep_map cpuhp_state_down_map =
99 STATIC_LOCKDEP_MAP_INIT("cpuhp_state-down", &cpuhp_state_down_map);
100
101
102static inline void cpuhp_lock_acquire(bool bringup)
103{
104 lock_map_acquire(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
105}
106
107static inline void cpuhp_lock_release(bool bringup)
108{
109 lock_map_release(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
110}
111#else
112
113static inline void cpuhp_lock_acquire(bool bringup) { }
114static inline void cpuhp_lock_release(bool bringup) { }
115
116#endif
117
118/**
119 * struct cpuhp_step - Hotplug state machine step
120 * @name: Name of the step
121 * @startup: Startup function of the step
122 * @teardown: Teardown function of the step
123 * @cant_stop: Bringup/teardown can't be stopped at this step
124 * @multi_instance: State has multiple instances which get added afterwards
125 */
126struct cpuhp_step {
127 const char *name;
128 union {
129 int (*single)(unsigned int cpu);
130 int (*multi)(unsigned int cpu,
131 struct hlist_node *node);
132 } startup;
133 union {
134 int (*single)(unsigned int cpu);
135 int (*multi)(unsigned int cpu,
136 struct hlist_node *node);
137 } teardown;
138 /* private: */
139 struct hlist_head list;
140 /* public: */
141 bool cant_stop;
142 bool multi_instance;
143};
144
145static DEFINE_MUTEX(cpuhp_state_mutex);
146static struct cpuhp_step cpuhp_hp_states[];
147
148static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
149{
150 return cpuhp_hp_states + state;
151}
152
153static bool cpuhp_step_empty(bool bringup, struct cpuhp_step *step)
154{
155 return bringup ? !step->startup.single : !step->teardown.single;
156}
157
158/**
159 * cpuhp_invoke_callback - Invoke the callbacks for a given state
160 * @cpu: The cpu for which the callback should be invoked
161 * @state: The state to do callbacks for
162 * @bringup: True if the bringup callback should be invoked
163 * @node: For multi-instance, do a single entry callback for install/remove
164 * @lastp: For multi-instance rollback, remember how far we got
165 *
166 * Called from cpu hotplug and from the state register machinery.
167 *
168 * Return: %0 on success or a negative errno code
169 */
170static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
171 bool bringup, struct hlist_node *node,
172 struct hlist_node **lastp)
173{
174 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
175 struct cpuhp_step *step = cpuhp_get_step(state);
176 int (*cbm)(unsigned int cpu, struct hlist_node *node);
177 int (*cb)(unsigned int cpu);
178 int ret, cnt;
179
180 if (st->fail == state) {
181 st->fail = CPUHP_INVALID;
182 return -EAGAIN;
183 }
184
185 if (cpuhp_step_empty(bringup, step)) {
186 WARN_ON_ONCE(1);
187 return 0;
188 }
189
190 if (!step->multi_instance) {
191 WARN_ON_ONCE(lastp && *lastp);
192 cb = bringup ? step->startup.single : step->teardown.single;
193
194 trace_cpuhp_enter(cpu, target: st->target, idx: state, fun: cb);
195 ret = cb(cpu);
196 trace_cpuhp_exit(cpu, state: st->state, idx: state, ret);
197 return ret;
198 }
199 cbm = bringup ? step->startup.multi : step->teardown.multi;
200
201 /* Single invocation for instance add/remove */
202 if (node) {
203 WARN_ON_ONCE(lastp && *lastp);
204 trace_cpuhp_multi_enter(cpu, target: st->target, idx: state, fun: cbm, node);
205 ret = cbm(cpu, node);
206 trace_cpuhp_exit(cpu, state: st->state, idx: state, ret);
207 return ret;
208 }
209
210 /* State transition. Invoke on all instances */
211 cnt = 0;
212 hlist_for_each(node, &step->list) {
213 if (lastp && node == *lastp)
214 break;
215
216 trace_cpuhp_multi_enter(cpu, target: st->target, idx: state, fun: cbm, node);
217 ret = cbm(cpu, node);
218 trace_cpuhp_exit(cpu, state: st->state, idx: state, ret);
219 if (ret) {
220 if (!lastp)
221 goto err;
222
223 *lastp = node;
224 return ret;
225 }
226 cnt++;
227 }
228 if (lastp)
229 *lastp = NULL;
230 return 0;
231err:
232 /* Rollback the instances if one failed */
233 cbm = !bringup ? step->startup.multi : step->teardown.multi;
234 if (!cbm)
235 return ret;
236
237 hlist_for_each(node, &step->list) {
238 if (!cnt--)
239 break;
240
241 trace_cpuhp_multi_enter(cpu, target: st->target, idx: state, fun: cbm, node);
242 ret = cbm(cpu, node);
243 trace_cpuhp_exit(cpu, state: st->state, idx: state, ret);
244 /*
245 * Rollback must not fail,
246 */
247 WARN_ON_ONCE(ret);
248 }
249 return ret;
250}
251
252#ifdef CONFIG_SMP
253static bool cpuhp_is_ap_state(enum cpuhp_state state)
254{
255 /*
256 * The extra check for CPUHP_TEARDOWN_CPU is only for documentation
257 * purposes as that state is handled explicitly in cpu_down.
258 */
259 return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
260}
261
262static inline void wait_for_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
263{
264 struct completion *done = bringup ? &st->done_up : &st->done_down;
265 wait_for_completion(done);
266}
267
268static inline void complete_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
269{
270 struct completion *done = bringup ? &st->done_up : &st->done_down;
271 complete(done);
272}
273
274/*
275 * The former STARTING/DYING states, ran with IRQs disabled and must not fail.
276 */
277static bool cpuhp_is_atomic_state(enum cpuhp_state state)
278{
279 return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
280}
281
282/* Synchronization state management */
283enum cpuhp_sync_state {
284 SYNC_STATE_DEAD,
285 SYNC_STATE_KICKED,
286 SYNC_STATE_SHOULD_DIE,
287 SYNC_STATE_ALIVE,
288 SYNC_STATE_SHOULD_ONLINE,
289 SYNC_STATE_ONLINE,
290};
291
292#ifdef CONFIG_HOTPLUG_CORE_SYNC
293/**
294 * cpuhp_ap_update_sync_state - Update synchronization state during bringup/teardown
295 * @state: The synchronization state to set
296 *
297 * No synchronization point. Just update of the synchronization state, but implies
298 * a full barrier so that the AP changes are visible before the control CPU proceeds.
299 */
300static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state)
301{
302 atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);
303
304 (void)atomic_xchg(v: st, new: state);
305}
306
307void __weak arch_cpuhp_sync_state_poll(void) { cpu_relax(); }
308
309static bool cpuhp_wait_for_sync_state(unsigned int cpu, enum cpuhp_sync_state state,
310 enum cpuhp_sync_state next_state)
311{
312 atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
313 ktime_t now, end, start = ktime_get();
314 int sync;
315
316 end = start + 10ULL * NSEC_PER_SEC;
317
318 sync = atomic_read(v: st);
319 while (1) {
320 if (sync == state) {
321 if (!atomic_try_cmpxchg(v: st, old: &sync, new: next_state))
322 continue;
323 return true;
324 }
325
326 now = ktime_get();
327 if (now > end) {
328 /* Timeout. Leave the state unchanged */
329 return false;
330 } else if (now - start < NSEC_PER_MSEC) {
331 /* Poll for one millisecond */
332 arch_cpuhp_sync_state_poll();
333 } else {
334 usleep_range(USEC_PER_MSEC, max: 2 * USEC_PER_MSEC);
335 }
336 sync = atomic_read(v: st);
337 }
338 return true;
339}
340#else /* CONFIG_HOTPLUG_CORE_SYNC */
341static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state) { }
342#endif /* !CONFIG_HOTPLUG_CORE_SYNC */
343
344#ifdef CONFIG_HOTPLUG_CORE_SYNC_DEAD
345/**
346 * cpuhp_ap_report_dead - Update synchronization state to DEAD
347 *
348 * No synchronization point. Just update of the synchronization state.
349 */
350void cpuhp_ap_report_dead(void)
351{
352 cpuhp_ap_update_sync_state(state: SYNC_STATE_DEAD);
353}
354
355void __weak arch_cpuhp_cleanup_dead_cpu(unsigned int cpu) { }
356
357/*
358 * Late CPU shutdown synchronization point. Cannot use cpuhp_state::done_down
359 * because the AP cannot issue complete() at this stage.
360 */
361static void cpuhp_bp_sync_dead(unsigned int cpu)
362{
363 atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
364 int sync = atomic_read(v: st);
365
366 do {
367 /* CPU can have reported dead already. Don't overwrite that! */
368 if (sync == SYNC_STATE_DEAD)
369 break;
370 } while (!atomic_try_cmpxchg(v: st, old: &sync, new: SYNC_STATE_SHOULD_DIE));
371
372 if (cpuhp_wait_for_sync_state(cpu, state: SYNC_STATE_DEAD, next_state: SYNC_STATE_DEAD)) {
373 /* CPU reached dead state. Invoke the cleanup function */
374 arch_cpuhp_cleanup_dead_cpu(cpu);
375 return;
376 }
377
378 /* No further action possible. Emit message and give up. */
379 pr_err("CPU%u failed to report dead state\n", cpu);
380}
381#else /* CONFIG_HOTPLUG_CORE_SYNC_DEAD */
382static inline void cpuhp_bp_sync_dead(unsigned int cpu) { }
383#endif /* !CONFIG_HOTPLUG_CORE_SYNC_DEAD */
384
385#ifdef CONFIG_HOTPLUG_CORE_SYNC_FULL
386/**
387 * cpuhp_ap_sync_alive - Synchronize AP with the control CPU once it is alive
388 *
389 * Updates the AP synchronization state to SYNC_STATE_ALIVE and waits
390 * for the BP to release it.
391 */
392void cpuhp_ap_sync_alive(void)
393{
394 atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);
395
396 cpuhp_ap_update_sync_state(state: SYNC_STATE_ALIVE);
397
398 /* Wait for the control CPU to release it. */
399 while (atomic_read(v: st) != SYNC_STATE_SHOULD_ONLINE)
400 cpu_relax();
401}
402
403static bool cpuhp_can_boot_ap(unsigned int cpu)
404{
405 atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
406 int sync = atomic_read(v: st);
407
408again:
409 switch (sync) {
410 case SYNC_STATE_DEAD:
411 /* CPU is properly dead */
412 break;
413 case SYNC_STATE_KICKED:
414 /* CPU did not come up in previous attempt */
415 break;
416 case SYNC_STATE_ALIVE:
417 /* CPU is stuck cpuhp_ap_sync_alive(). */
418 break;
419 default:
420 /* CPU failed to report online or dead and is in limbo state. */
421 return false;
422 }
423
424 /* Prepare for booting */
425 if (!atomic_try_cmpxchg(v: st, old: &sync, new: SYNC_STATE_KICKED))
426 goto again;
427
428 return true;
429}
430
431void __weak arch_cpuhp_cleanup_kick_cpu(unsigned int cpu) { }
432
433/*
434 * Early CPU bringup synchronization point. Cannot use cpuhp_state::done_up
435 * because the AP cannot issue complete() so early in the bringup.
436 */
437static int cpuhp_bp_sync_alive(unsigned int cpu)
438{
439 int ret = 0;
440
441 if (!IS_ENABLED(CONFIG_HOTPLUG_CORE_SYNC_FULL))
442 return 0;
443
444 if (!cpuhp_wait_for_sync_state(cpu, state: SYNC_STATE_ALIVE, next_state: SYNC_STATE_SHOULD_ONLINE)) {
445 pr_err("CPU%u failed to report alive state\n", cpu);
446 ret = -EIO;
447 }
448
449 /* Let the architecture cleanup the kick alive mechanics. */
450 arch_cpuhp_cleanup_kick_cpu(cpu);
451 return ret;
452}
453#else /* CONFIG_HOTPLUG_CORE_SYNC_FULL */
454static inline int cpuhp_bp_sync_alive(unsigned int cpu) { return 0; }
455static inline bool cpuhp_can_boot_ap(unsigned int cpu) { return true; }
456#endif /* !CONFIG_HOTPLUG_CORE_SYNC_FULL */
457
458/* Serializes the updates to cpu_online_mask, cpu_present_mask */
459static DEFINE_MUTEX(cpu_add_remove_lock);
460bool cpuhp_tasks_frozen;
461EXPORT_SYMBOL_GPL(cpuhp_tasks_frozen);
462
463/*
464 * The following two APIs (cpu_maps_update_begin/done) must be used when
465 * attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
466 */
467void cpu_maps_update_begin(void)
468{
469 mutex_lock(lock: &cpu_add_remove_lock);
470}
471
472void cpu_maps_update_done(void)
473{
474 mutex_unlock(lock: &cpu_add_remove_lock);
475}
476
477/*
478 * If set, cpu_up and cpu_down will return -EBUSY and do nothing.
479 * Should always be manipulated under cpu_add_remove_lock
480 */
481static int cpu_hotplug_disabled;
482
483#ifdef CONFIG_HOTPLUG_CPU
484
485DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
486
487static bool cpu_hotplug_offline_disabled __ro_after_init;
488
489void cpus_read_lock(void)
490{
491 percpu_down_read(sem: &cpu_hotplug_lock);
492}
493EXPORT_SYMBOL_GPL(cpus_read_lock);
494
495int cpus_read_trylock(void)
496{
497 return percpu_down_read_trylock(sem: &cpu_hotplug_lock);
498}
499EXPORT_SYMBOL_GPL(cpus_read_trylock);
500
501void cpus_read_unlock(void)
502{
503 percpu_up_read(sem: &cpu_hotplug_lock);
504}
505EXPORT_SYMBOL_GPL(cpus_read_unlock);
506
507void cpus_write_lock(void)
508{
509 percpu_down_write(&cpu_hotplug_lock);
510}
511
512void cpus_write_unlock(void)
513{
514 percpu_up_write(&cpu_hotplug_lock);
515}
516
517void lockdep_assert_cpus_held(void)
518{
519 /*
520 * We can't have hotplug operations before userspace starts running,
521 * and some init codepaths will knowingly not take the hotplug lock.
522 * This is all valid, so mute lockdep until it makes sense to report
523 * unheld locks.
524 */
525 if (system_state < SYSTEM_RUNNING)
526 return;
527
528 percpu_rwsem_assert_held(&cpu_hotplug_lock);
529}
530EXPORT_SYMBOL_GPL(lockdep_assert_cpus_held);
531
532#ifdef CONFIG_LOCKDEP
533int lockdep_is_cpus_held(void)
534{
535 return percpu_rwsem_is_held(&cpu_hotplug_lock);
536}
537#endif
538
539static void lockdep_acquire_cpus_lock(void)
540{
541 rwsem_acquire(&cpu_hotplug_lock.dep_map, 0, 0, _THIS_IP_);
542}
543
544static void lockdep_release_cpus_lock(void)
545{
546 rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_);
547}
548
549/* Declare CPU offlining not supported */
550void cpu_hotplug_disable_offlining(void)
551{
552 cpu_maps_update_begin();
553 cpu_hotplug_offline_disabled = true;
554 cpu_maps_update_done();
555}
556
557/*
558 * Wait for currently running CPU hotplug operations to complete (if any) and
559 * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
560 * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
561 * hotplug path before performing hotplug operations. So acquiring that lock
562 * guarantees mutual exclusion from any currently running hotplug operations.
563 */
564void cpu_hotplug_disable(void)
565{
566 cpu_maps_update_begin();
567 cpu_hotplug_disabled++;
568 cpu_maps_update_done();
569}
570EXPORT_SYMBOL_GPL(cpu_hotplug_disable);
571
572static void __cpu_hotplug_enable(void)
573{
574 if (WARN_ONCE(!cpu_hotplug_disabled, "Unbalanced cpu hotplug enable\n"))
575 return;
576 cpu_hotplug_disabled--;
577}
578
579void cpu_hotplug_enable(void)
580{
581 cpu_maps_update_begin();
582 __cpu_hotplug_enable();
583 cpu_maps_update_done();
584}
585EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
586
587#else
588
589static void lockdep_acquire_cpus_lock(void)
590{
591}
592
593static void lockdep_release_cpus_lock(void)
594{
595}
596
597#endif /* CONFIG_HOTPLUG_CPU */
598
599/*
600 * Architectures that need SMT-specific errata handling during SMT hotplug
601 * should override this.
602 */
603void __weak arch_smt_update(void) { }
604
605#ifdef CONFIG_HOTPLUG_SMT
606
607enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
608static unsigned int cpu_smt_max_threads __ro_after_init;
609unsigned int cpu_smt_num_threads __read_mostly = UINT_MAX;
610
611void __init cpu_smt_disable(bool force)
612{
613 if (!cpu_smt_possible())
614 return;
615
616 if (force) {
617 pr_info("SMT: Force disabled\n");
618 cpu_smt_control = CPU_SMT_FORCE_DISABLED;
619 } else {
620 pr_info("SMT: disabled\n");
621 cpu_smt_control = CPU_SMT_DISABLED;
622 }
623 cpu_smt_num_threads = 1;
624}
625
626/*
627 * The decision whether SMT is supported can only be done after the full
628 * CPU identification. Called from architecture code.
629 */
630void __init cpu_smt_set_num_threads(unsigned int num_threads,
631 unsigned int max_threads)
632{
633 WARN_ON(!num_threads || (num_threads > max_threads));
634
635 if (max_threads == 1)
636 cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
637
638 cpu_smt_max_threads = max_threads;
639
640 /*
641 * If SMT has been disabled via the kernel command line or SMT is
642 * not supported, set cpu_smt_num_threads to 1 for consistency.
643 * If enabled, take the architecture requested number of threads
644 * to bring up into account.
645 */
646 if (cpu_smt_control != CPU_SMT_ENABLED)
647 cpu_smt_num_threads = 1;
648 else if (num_threads < cpu_smt_num_threads)
649 cpu_smt_num_threads = num_threads;
650}
651
652static int __init smt_cmdline_disable(char *str)
653{
654 cpu_smt_disable(force: str && !strcmp(str, "force"));
655 return 0;
656}
657early_param("nosmt", smt_cmdline_disable);
658
659/*
660 * For Archicture supporting partial SMT states check if the thread is allowed.
661 * Otherwise this has already been checked through cpu_smt_max_threads when
662 * setting the SMT level.
663 */
664static inline bool cpu_smt_thread_allowed(unsigned int cpu)
665{
666#ifdef CONFIG_SMT_NUM_THREADS_DYNAMIC
667 return topology_smt_thread_allowed(cpu);
668#else
669 return true;
670#endif
671}
672
673static inline bool cpu_bootable(unsigned int cpu)
674{
675 if (cpu_smt_control == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu))
676 return true;
677
678 /* All CPUs are bootable if controls are not configured */
679 if (cpu_smt_control == CPU_SMT_NOT_IMPLEMENTED)
680 return true;
681
682 /* All CPUs are bootable if CPU is not SMT capable */
683 if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
684 return true;
685
686 if (topology_is_primary_thread(cpu))
687 return true;
688
689 /*
690 * On x86 it's required to boot all logical CPUs at least once so
691 * that the init code can get a chance to set CR4.MCE on each
692 * CPU. Otherwise, a broadcasted MCE observing CR4.MCE=0b on any
693 * core will shutdown the machine.
694 */
695 return !cpumask_test_cpu(cpu, cpumask: &cpus_booted_once_mask);
696}
697
698/* Returns true if SMT is supported and not forcefully (irreversibly) disabled */
699bool cpu_smt_possible(void)
700{
701 return cpu_smt_control != CPU_SMT_FORCE_DISABLED &&
702 cpu_smt_control != CPU_SMT_NOT_SUPPORTED;
703}
704EXPORT_SYMBOL_GPL(cpu_smt_possible);
705
706#else
707static inline bool cpu_bootable(unsigned int cpu) { return true; }
708#endif
709
710static inline enum cpuhp_state
711cpuhp_set_state(int cpu, struct cpuhp_cpu_state *st, enum cpuhp_state target)
712{
713 enum cpuhp_state prev_state = st->state;
714 bool bringup = st->state < target;
715
716 st->rollback = false;
717 st->last = NULL;
718
719 st->target = target;
720 st->single = false;
721 st->bringup = bringup;
722 if (cpu_dying(cpu) != !bringup)
723 set_cpu_dying(cpu, !bringup);
724
725 return prev_state;
726}
727
728static inline void
729cpuhp_reset_state(int cpu, struct cpuhp_cpu_state *st,
730 enum cpuhp_state prev_state)
731{
732 bool bringup = !st->bringup;
733
734 st->target = prev_state;
735
736 /*
737 * Already rolling back. No need invert the bringup value or to change
738 * the current state.
739 */
740 if (st->rollback)
741 return;
742
743 st->rollback = true;
744
745 /*
746 * If we have st->last we need to undo partial multi_instance of this
747 * state first. Otherwise start undo at the previous state.
748 */
749 if (!st->last) {
750 if (st->bringup)
751 st->state--;
752 else
753 st->state++;
754 }
755
756 st->bringup = bringup;
757 if (cpu_dying(cpu) != !bringup)
758 set_cpu_dying(cpu, !bringup);
759}
760
761/* Regular hotplug invocation of the AP hotplug thread */
762static void __cpuhp_kick_ap(struct cpuhp_cpu_state *st)
763{
764 if (!st->single && st->state == st->target)
765 return;
766
767 st->result = 0;
768 /*
769 * Make sure the above stores are visible before should_run becomes
770 * true. Paired with the mb() above in cpuhp_thread_fun()
771 */
772 smp_mb();
773 st->should_run = true;
774 wake_up_process(tsk: st->thread);
775 wait_for_ap_thread(st, bringup: st->bringup);
776}
777
778static int cpuhp_kick_ap(int cpu, struct cpuhp_cpu_state *st,
779 enum cpuhp_state target)
780{
781 enum cpuhp_state prev_state;
782 int ret;
783
784 prev_state = cpuhp_set_state(cpu, st, target);
785 __cpuhp_kick_ap(st);
786 if ((ret = st->result)) {
787 cpuhp_reset_state(cpu, st, prev_state);
788 __cpuhp_kick_ap(st);
789 }
790
791 return ret;
792}
793
794static int bringup_wait_for_ap_online(unsigned int cpu)
795{
796 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
797
798 /* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
799 wait_for_ap_thread(st, bringup: true);
800 if (WARN_ON_ONCE((!cpu_online(cpu))))
801 return -ECANCELED;
802
803 /* Unpark the hotplug thread of the target cpu */
804 kthread_unpark(k: st->thread);
805
806 /*
807 * SMT soft disabling on X86 requires to bring the CPU out of the
808 * BIOS 'wait for SIPI' state in order to set the CR4.MCE bit. The
809 * CPU marked itself as booted_once in notify_cpu_starting() so the
810 * cpu_bootable() check will now return false if this is not the
811 * primary sibling.
812 */
813 if (!cpu_bootable(cpu))
814 return -ECANCELED;
815 return 0;
816}
817
818#ifdef CONFIG_HOTPLUG_SPLIT_STARTUP
819static int cpuhp_kick_ap_alive(unsigned int cpu)
820{
821 if (!cpuhp_can_boot_ap(cpu))
822 return -EAGAIN;
823
824 return arch_cpuhp_kick_ap_alive(cpu, tidle: idle_thread_get(cpu));
825}
826
827static int cpuhp_bringup_ap(unsigned int cpu)
828{
829 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
830 int ret;
831
832 /*
833 * Some architectures have to walk the irq descriptors to
834 * setup the vector space for the cpu which comes online.
835 * Prevent irq alloc/free across the bringup.
836 */
837 irq_lock_sparse();
838
839 ret = cpuhp_bp_sync_alive(cpu);
840 if (ret)
841 goto out_unlock;
842
843 ret = bringup_wait_for_ap_online(cpu);
844 if (ret)
845 goto out_unlock;
846
847 irq_unlock_sparse();
848
849 if (st->target <= CPUHP_AP_ONLINE_IDLE)
850 return 0;
851
852 return cpuhp_kick_ap(cpu, st, target: st->target);
853
854out_unlock:
855 irq_unlock_sparse();
856 return ret;
857}
858#else
859static int bringup_cpu(unsigned int cpu)
860{
861 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
862 struct task_struct *idle = idle_thread_get(cpu);
863 int ret;
864
865 if (!cpuhp_can_boot_ap(cpu))
866 return -EAGAIN;
867
868 /*
869 * Some architectures have to walk the irq descriptors to
870 * setup the vector space for the cpu which comes online.
871 *
872 * Prevent irq alloc/free across the bringup by acquiring the
873 * sparse irq lock. Hold it until the upcoming CPU completes the
874 * startup in cpuhp_online_idle() which allows to avoid
875 * intermediate synchronization points in the architecture code.
876 */
877 irq_lock_sparse();
878
879 ret = __cpu_up(cpu, idle);
880 if (ret)
881 goto out_unlock;
882
883 ret = cpuhp_bp_sync_alive(cpu);
884 if (ret)
885 goto out_unlock;
886
887 ret = bringup_wait_for_ap_online(cpu);
888 if (ret)
889 goto out_unlock;
890
891 irq_unlock_sparse();
892
893 if (st->target <= CPUHP_AP_ONLINE_IDLE)
894 return 0;
895
896 return cpuhp_kick_ap(cpu, st, st->target);
897
898out_unlock:
899 irq_unlock_sparse();
900 return ret;
901}
902#endif
903
904static int finish_cpu(unsigned int cpu)
905{
906 struct task_struct *idle = idle_thread_get(cpu);
907 struct mm_struct *mm = idle->active_mm;
908
909 /*
910 * sched_force_init_mm() ensured the use of &init_mm,
911 * drop that refcount now that the CPU has stopped.
912 */
913 WARN_ON(mm != &init_mm);
914 idle->active_mm = NULL;
915 mmdrop_lazy_tlb(mm);
916
917 return 0;
918}
919
920/*
921 * Hotplug state machine related functions
922 */
923
924/*
925 * Get the next state to run. Empty ones will be skipped. Returns true if a
926 * state must be run.
927 *
928 * st->state will be modified ahead of time, to match state_to_run, as if it
929 * has already ran.
930 */
931static bool cpuhp_next_state(bool bringup,
932 enum cpuhp_state *state_to_run,
933 struct cpuhp_cpu_state *st,
934 enum cpuhp_state target)
935{
936 do {
937 if (bringup) {
938 if (st->state >= target)
939 return false;
940
941 *state_to_run = ++st->state;
942 } else {
943 if (st->state <= target)
944 return false;
945
946 *state_to_run = st->state--;
947 }
948
949 if (!cpuhp_step_empty(bringup, step: cpuhp_get_step(state: *state_to_run)))
950 break;
951 } while (true);
952
953 return true;
954}
955
956static int __cpuhp_invoke_callback_range(bool bringup,
957 unsigned int cpu,
958 struct cpuhp_cpu_state *st,
959 enum cpuhp_state target,
960 bool nofail)
961{
962 enum cpuhp_state state;
963 int ret = 0;
964
965 while (cpuhp_next_state(bringup, state_to_run: &state, st, target)) {
966 int err;
967
968 err = cpuhp_invoke_callback(cpu, state, bringup, NULL, NULL);
969 if (!err)
970 continue;
971
972 if (nofail) {
973 pr_warn("CPU %u %s state %s (%d) failed (%d)\n",
974 cpu, bringup ? "UP" : "DOWN",
975 cpuhp_get_step(st->state)->name,
976 st->state, err);
977 ret = -1;
978 } else {
979 ret = err;
980 break;
981 }
982 }
983
984 return ret;
985}
986
987static inline int cpuhp_invoke_callback_range(bool bringup,
988 unsigned int cpu,
989 struct cpuhp_cpu_state *st,
990 enum cpuhp_state target)
991{
992 return __cpuhp_invoke_callback_range(bringup, cpu, st, target, nofail: false);
993}
994
995static inline void cpuhp_invoke_callback_range_nofail(bool bringup,
996 unsigned int cpu,
997 struct cpuhp_cpu_state *st,
998 enum cpuhp_state target)
999{
1000 __cpuhp_invoke_callback_range(bringup, cpu, st, target, nofail: true);
1001}
1002
1003static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
1004{
1005 if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
1006 return true;
1007 /*
1008 * When CPU hotplug is disabled, then taking the CPU down is not
1009 * possible because takedown_cpu() and the architecture and
1010 * subsystem specific mechanisms are not available. So the CPU
1011 * which would be completely unplugged again needs to stay around
1012 * in the current state.
1013 */
1014 return st->state <= CPUHP_BRINGUP_CPU;
1015}
1016
1017static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
1018 enum cpuhp_state target)
1019{
1020 enum cpuhp_state prev_state = st->state;
1021 int ret = 0;
1022
1023 ret = cpuhp_invoke_callback_range(bringup: true, cpu, st, target);
1024 if (ret) {
1025 pr_debug("CPU UP failed (%d) CPU %u state %s (%d)\n",
1026 ret, cpu, cpuhp_get_step(st->state)->name,
1027 st->state);
1028
1029 cpuhp_reset_state(cpu, st, prev_state);
1030 if (can_rollback_cpu(st))
1031 WARN_ON(cpuhp_invoke_callback_range(false, cpu, st,
1032 prev_state));
1033 }
1034 return ret;
1035}
1036
1037/*
1038 * The cpu hotplug threads manage the bringup and teardown of the cpus
1039 */
1040static int cpuhp_should_run(unsigned int cpu)
1041{
1042 struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
1043
1044 return st->should_run;
1045}
1046
1047/*
1048 * Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
1049 * callbacks when a state gets [un]installed at runtime.
1050 *
1051 * Each invocation of this function by the smpboot thread does a single AP
1052 * state callback.
1053 *
1054 * It has 3 modes of operation:
1055 * - single: runs st->cb_state
1056 * - up: runs ++st->state, while st->state < st->target
1057 * - down: runs st->state--, while st->state > st->target
1058 *
1059 * When complete or on error, should_run is cleared and the completion is fired.
1060 */
1061static void cpuhp_thread_fun(unsigned int cpu)
1062{
1063 struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
1064 bool bringup = st->bringup;
1065 enum cpuhp_state state;
1066
1067 if (WARN_ON_ONCE(!st->should_run))
1068 return;
1069
1070 /*
1071 * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
1072 * that if we see ->should_run we also see the rest of the state.
1073 */
1074 smp_mb();
1075
1076 /*
1077 * The BP holds the hotplug lock, but we're now running on the AP,
1078 * ensure that anybody asserting the lock is held, will actually find
1079 * it so.
1080 */
1081 lockdep_acquire_cpus_lock();
1082 cpuhp_lock_acquire(bringup);
1083
1084 if (st->single) {
1085 state = st->cb_state;
1086 st->should_run = false;
1087 } else {
1088 st->should_run = cpuhp_next_state(bringup, state_to_run: &state, st, target: st->target);
1089 if (!st->should_run)
1090 goto end;
1091 }
1092
1093 WARN_ON_ONCE(!cpuhp_is_ap_state(state));
1094
1095 if (cpuhp_is_atomic_state(state)) {
1096 local_irq_disable();
1097 st->result = cpuhp_invoke_callback(cpu, state, bringup, node: st->node, lastp: &st->last);
1098 local_irq_enable();
1099
1100 /*
1101 * STARTING/DYING must not fail!
1102 */
1103 WARN_ON_ONCE(st->result);
1104 } else {
1105 st->result = cpuhp_invoke_callback(cpu, state, bringup, node: st->node, lastp: &st->last);
1106 }
1107
1108 if (st->result) {
1109 /*
1110 * If we fail on a rollback, we're up a creek without no
1111 * paddle, no way forward, no way back. We loose, thanks for
1112 * playing.
1113 */
1114 WARN_ON_ONCE(st->rollback);
1115 st->should_run = false;
1116 }
1117
1118end:
1119 cpuhp_lock_release(bringup);
1120 lockdep_release_cpus_lock();
1121
1122 if (!st->should_run)
1123 complete_ap_thread(st, bringup);
1124}
1125
1126/* Invoke a single callback on a remote cpu */
1127static int
1128cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
1129 struct hlist_node *node)
1130{
1131 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
1132 int ret;
1133
1134 if (!cpu_online(cpu))
1135 return 0;
1136
1137 cpuhp_lock_acquire(bringup: false);
1138 cpuhp_lock_release(bringup: false);
1139
1140 cpuhp_lock_acquire(bringup: true);
1141 cpuhp_lock_release(bringup: true);
1142
1143 /*
1144 * If we are up and running, use the hotplug thread. For early calls
1145 * we invoke the thread function directly.
1146 */
1147 if (!st->thread)
1148 return cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
1149
1150 st->rollback = false;
1151 st->last = NULL;
1152
1153 st->node = node;
1154 st->bringup = bringup;
1155 st->cb_state = state;
1156 st->single = true;
1157
1158 __cpuhp_kick_ap(st);
1159
1160 /*
1161 * If we failed and did a partial, do a rollback.
1162 */
1163 if ((ret = st->result) && st->last) {
1164 st->rollback = true;
1165 st->bringup = !bringup;
1166
1167 __cpuhp_kick_ap(st);
1168 }
1169
1170 /*
1171 * Clean up the leftovers so the next hotplug operation wont use stale
1172 * data.
1173 */
1174 st->node = st->last = NULL;
1175 return ret;
1176}
1177
1178static int cpuhp_kick_ap_work(unsigned int cpu)
1179{
1180 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
1181 enum cpuhp_state prev_state = st->state;
1182 int ret;
1183
1184 cpuhp_lock_acquire(bringup: false);
1185 cpuhp_lock_release(bringup: false);
1186
1187 cpuhp_lock_acquire(bringup: true);
1188 cpuhp_lock_release(bringup: true);
1189
1190 trace_cpuhp_enter(cpu, target: st->target, idx: prev_state, fun: cpuhp_kick_ap_work);
1191 ret = cpuhp_kick_ap(cpu, st, target: st->target);
1192 trace_cpuhp_exit(cpu, state: st->state, idx: prev_state, ret);
1193
1194 return ret;
1195}
1196
1197static struct smp_hotplug_thread cpuhp_threads = {
1198 .store = &cpuhp_state.thread,
1199 .thread_should_run = cpuhp_should_run,
1200 .thread_fn = cpuhp_thread_fun,
1201 .thread_comm = "cpuhp/%u",
1202 .selfparking = true,
1203};
1204
1205static __init void cpuhp_init_state(void)
1206{
1207 struct cpuhp_cpu_state *st;
1208 int cpu;
1209
1210 for_each_possible_cpu(cpu) {
1211 st = per_cpu_ptr(&cpuhp_state, cpu);
1212 init_completion(x: &st->done_up);
1213 init_completion(x: &st->done_down);
1214 }
1215}
1216
1217void __init cpuhp_threads_init(void)
1218{
1219 cpuhp_init_state();
1220 BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
1221 kthread_unpark(this_cpu_read(cpuhp_state.thread));
1222}
1223
1224#ifdef CONFIG_HOTPLUG_CPU
1225#ifndef arch_clear_mm_cpumask_cpu
1226#define arch_clear_mm_cpumask_cpu(cpu, mm) cpumask_clear_cpu(cpu, mm_cpumask(mm))
1227#endif
1228
1229/**
1230 * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
1231 * @cpu: a CPU id
1232 *
1233 * This function walks all processes, finds a valid mm struct for each one and
1234 * then clears a corresponding bit in mm's cpumask. While this all sounds
1235 * trivial, there are various non-obvious corner cases, which this function
1236 * tries to solve in a safe manner.
1237 *
1238 * Also note that the function uses a somewhat relaxed locking scheme, so it may
1239 * be called only for an already offlined CPU.
1240 */
1241void clear_tasks_mm_cpumask(int cpu)
1242{
1243 struct task_struct *p;
1244
1245 /*
1246 * This function is called after the cpu is taken down and marked
1247 * offline, so its not like new tasks will ever get this cpu set in
1248 * their mm mask. -- Peter Zijlstra
1249 * Thus, we may use rcu_read_lock() here, instead of grabbing
1250 * full-fledged tasklist_lock.
1251 */
1252 WARN_ON(cpu_online(cpu));
1253 rcu_read_lock();
1254 for_each_process(p) {
1255 struct task_struct *t;
1256
1257 /*
1258 * Main thread might exit, but other threads may still have
1259 * a valid mm. Find one.
1260 */
1261 t = find_lock_task_mm(p);
1262 if (!t)
1263 continue;
1264 arch_clear_mm_cpumask_cpu(cpu, t->mm);
1265 task_unlock(p: t);
1266 }
1267 rcu_read_unlock();
1268}
1269
1270/* Take this CPU down. */
1271static int take_cpu_down(void *_param)
1272{
1273 struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
1274 enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
1275 int err, cpu = smp_processor_id();
1276
1277 /* Ensure this CPU doesn't handle any more interrupts. */
1278 err = __cpu_disable();
1279 if (err < 0)
1280 return err;
1281
1282 /*
1283 * Must be called from CPUHP_TEARDOWN_CPU, which means, as we are going
1284 * down, that the current state is CPUHP_TEARDOWN_CPU - 1.
1285 */
1286 WARN_ON(st->state != (CPUHP_TEARDOWN_CPU - 1));
1287
1288 /*
1289 * Invoke the former CPU_DYING callbacks. DYING must not fail!
1290 */
1291 cpuhp_invoke_callback_range_nofail(bringup: false, cpu, st, target);
1292
1293 /* Park the stopper thread */
1294 stop_machine_park(cpu);
1295 return 0;
1296}
1297
1298static int takedown_cpu(unsigned int cpu)
1299{
1300 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
1301 int err;
1302
1303 /* Park the smpboot threads */
1304 kthread_park(k: st->thread);
1305
1306 /*
1307 * Prevent irq alloc/free while the dying cpu reorganizes the
1308 * interrupt affinities.
1309 */
1310 irq_lock_sparse();
1311
1312 err = stop_machine_cpuslocked(fn: take_cpu_down, NULL, cpumask_of(cpu));
1313 if (err) {
1314 /* CPU refused to die */
1315 irq_unlock_sparse();
1316 /* Unpark the hotplug thread so we can rollback there */
1317 kthread_unpark(k: st->thread);
1318 return err;
1319 }
1320 BUG_ON(cpu_online(cpu));
1321
1322 /*
1323 * The teardown callback for CPUHP_AP_SCHED_STARTING will have removed
1324 * all runnable tasks from the CPU, there's only the idle task left now
1325 * that the migration thread is done doing the stop_machine thing.
1326 *
1327 * Wait for the stop thread to go away.
1328 */
1329 wait_for_ap_thread(st, bringup: false);
1330 BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);
1331
1332 /* Interrupts are moved away from the dying cpu, reenable alloc/free */
1333 irq_unlock_sparse();
1334
1335 hotplug_cpu__broadcast_tick_pull(dead_cpu: cpu);
1336 /* This actually kills the CPU. */
1337 __cpu_die(cpu);
1338
1339 cpuhp_bp_sync_dead(cpu);
1340
1341 lockdep_cleanup_dead_cpu(cpu, idle: idle_thread_get(cpu));
1342
1343 /*
1344 * Callbacks must be re-integrated right away to the RCU state machine.
1345 * Otherwise an RCU callback could block a further teardown function
1346 * waiting for its completion.
1347 */
1348 rcutree_migrate_callbacks(cpu);
1349
1350 return 0;
1351}
1352
1353static void cpuhp_complete_idle_dead(void *arg)
1354{
1355 struct cpuhp_cpu_state *st = arg;
1356
1357 complete_ap_thread(st, bringup: false);
1358}
1359
1360void cpuhp_report_idle_dead(void)
1361{
1362 struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
1363
1364 BUG_ON(st->state != CPUHP_AP_OFFLINE);
1365 tick_assert_timekeeping_handover();
1366 rcutree_report_cpu_dead();
1367 st->state = CPUHP_AP_IDLE_DEAD;
1368 /*
1369 * We cannot call complete after rcutree_report_cpu_dead() so we delegate it
1370 * to an online cpu.
1371 */
1372 smp_call_function_single(cpuid: cpumask_first(cpu_online_mask),
1373 func: cpuhp_complete_idle_dead, info: st, wait: 0);
1374}
1375
1376static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
1377 enum cpuhp_state target)
1378{
1379 enum cpuhp_state prev_state = st->state;
1380 int ret = 0;
1381
1382 ret = cpuhp_invoke_callback_range(bringup: false, cpu, st, target);
1383 if (ret) {
1384 pr_debug("CPU DOWN failed (%d) CPU %u state %s (%d)\n",
1385 ret, cpu, cpuhp_get_step(st->state)->name,
1386 st->state);
1387
1388 cpuhp_reset_state(cpu, st, prev_state);
1389
1390 if (st->state < prev_state)
1391 WARN_ON(cpuhp_invoke_callback_range(true, cpu, st,
1392 prev_state));
1393 }
1394
1395 return ret;
1396}
1397
1398/* Requires cpu_add_remove_lock to be held */
1399static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
1400 enum cpuhp_state target)
1401{
1402 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
1403 int prev_state, ret = 0;
1404
1405 if (num_online_cpus() == 1)
1406 return -EBUSY;
1407
1408 if (!cpu_present(cpu))
1409 return -EINVAL;
1410
1411 cpus_write_lock();
1412
1413 cpuhp_tasks_frozen = tasks_frozen;
1414
1415 prev_state = cpuhp_set_state(cpu, st, target);
1416 /*
1417 * If the current CPU state is in the range of the AP hotplug thread,
1418 * then we need to kick the thread.
1419 */
1420 if (st->state > CPUHP_TEARDOWN_CPU) {
1421 st->target = max((int)target, CPUHP_TEARDOWN_CPU);
1422 ret = cpuhp_kick_ap_work(cpu);
1423 /*
1424 * The AP side has done the error rollback already. Just
1425 * return the error code..
1426 */
1427 if (ret)
1428 goto out;
1429
1430 /*
1431 * We might have stopped still in the range of the AP hotplug
1432 * thread. Nothing to do anymore.
1433 */
1434 if (st->state > CPUHP_TEARDOWN_CPU)
1435 goto out;
1436
1437 st->target = target;
1438 }
1439 /*
1440 * The AP brought itself down to CPUHP_TEARDOWN_CPU. So we need
1441 * to do the further cleanups.
1442 */
1443 ret = cpuhp_down_callbacks(cpu, st, target);
1444 if (ret && st->state < prev_state) {
1445 if (st->state == CPUHP_TEARDOWN_CPU) {
1446 cpuhp_reset_state(cpu, st, prev_state);
1447 __cpuhp_kick_ap(st);
1448 } else {
1449 WARN(1, "DEAD callback error for CPU%d", cpu);
1450 }
1451 }
1452
1453out:
1454 cpus_write_unlock();
1455 arch_smt_update();
1456 return ret;
1457}
1458
1459struct cpu_down_work {
1460 unsigned int cpu;
1461 enum cpuhp_state target;
1462};
1463
1464static long __cpu_down_maps_locked(void *arg)
1465{
1466 struct cpu_down_work *work = arg;
1467
1468 return _cpu_down(cpu: work->cpu, tasks_frozen: 0, target: work->target);
1469}
1470
1471static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
1472{
1473 struct cpu_down_work work = { .cpu = cpu, .target = target, };
1474
1475 /*
1476 * If the platform does not support hotplug, report it explicitly to
1477 * differentiate it from a transient offlining failure.
1478 */
1479 if (cpu_hotplug_offline_disabled)
1480 return -EOPNOTSUPP;
1481 if (cpu_hotplug_disabled)
1482 return -EBUSY;
1483
1484 /*
1485 * Ensure that the control task does not run on the to be offlined
1486 * CPU to prevent a deadlock against cfs_b->period_timer.
1487 * Also keep at least one housekeeping cpu onlined to avoid generating
1488 * an empty sched_domain span.
1489 */
1490 for_each_cpu_and(cpu, cpu_online_mask, housekeeping_cpumask(HK_TYPE_DOMAIN)) {
1491 if (cpu != work.cpu)
1492 return work_on_cpu(cpu, __cpu_down_maps_locked, &work);
1493 }
1494 return -EBUSY;
1495}
1496
1497static int cpu_down(unsigned int cpu, enum cpuhp_state target)
1498{
1499 int err;
1500
1501 cpu_maps_update_begin();
1502 err = cpu_down_maps_locked(cpu, target);
1503 cpu_maps_update_done();
1504 return err;
1505}
1506
1507/**
1508 * cpu_device_down - Bring down a cpu device
1509 * @dev: Pointer to the cpu device to offline
1510 *
1511 * This function is meant to be used by device core cpu subsystem only.
1512 *
1513 * Other subsystems should use remove_cpu() instead.
1514 *
1515 * Return: %0 on success or a negative errno code
1516 */
1517int cpu_device_down(struct device *dev)
1518{
1519 return cpu_down(cpu: dev->id, target: CPUHP_OFFLINE);
1520}
1521
1522int remove_cpu(unsigned int cpu)
1523{
1524 int ret;
1525
1526 lock_device_hotplug();
1527 ret = device_offline(dev: get_cpu_device(cpu));
1528 unlock_device_hotplug();
1529
1530 return ret;
1531}
1532EXPORT_SYMBOL_GPL(remove_cpu);
1533
1534void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
1535{
1536 unsigned int cpu;
1537 int error;
1538
1539 cpu_maps_update_begin();
1540
1541 /*
1542 * Make certain the cpu I'm about to reboot on is online.
1543 *
1544 * This is inline to what migrate_to_reboot_cpu() already do.
1545 */
1546 if (!cpu_online(cpu: primary_cpu))
1547 primary_cpu = cpumask_first(cpu_online_mask);
1548
1549 for_each_online_cpu(cpu) {
1550 if (cpu == primary_cpu)
1551 continue;
1552
1553 error = cpu_down_maps_locked(cpu, target: CPUHP_OFFLINE);
1554 if (error) {
1555 pr_err("Failed to offline CPU%d - error=%d",
1556 cpu, error);
1557 break;
1558 }
1559 }
1560
1561 /*
1562 * Ensure all but the reboot CPU are offline.
1563 */
1564 BUG_ON(num_online_cpus() > 1);
1565
1566 /*
1567 * Make sure the CPUs won't be enabled by someone else after this
1568 * point. Kexec will reboot to a new kernel shortly resetting
1569 * everything along the way.
1570 */
1571 cpu_hotplug_disabled++;
1572
1573 cpu_maps_update_done();
1574}
1575
1576#else
1577#define takedown_cpu NULL
1578#endif /*CONFIG_HOTPLUG_CPU*/
1579
1580/**
1581 * notify_cpu_starting(cpu) - Invoke the callbacks on the starting CPU
1582 * @cpu: cpu that just started
1583 *
1584 * It must be called by the arch code on the new cpu, before the new cpu
1585 * enables interrupts and before the "boot" cpu returns from __cpu_up().
1586 */
1587void notify_cpu_starting(unsigned int cpu)
1588{
1589 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
1590 enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
1591
1592 rcutree_report_cpu_starting(cpu); /* Enables RCU usage on this CPU. */
1593 cpumask_set_cpu(cpu, dstp: &cpus_booted_once_mask);
1594
1595 /*
1596 * STARTING must not fail!
1597 */
1598 cpuhp_invoke_callback_range_nofail(bringup: true, cpu, st, target);
1599}
1600
1601/*
1602 * Called from the idle task. Wake up the controlling task which brings the
1603 * hotplug thread of the upcoming CPU up and then delegates the rest of the
1604 * online bringup to the hotplug thread.
1605 */
1606void cpuhp_online_idle(enum cpuhp_state state)
1607{
1608 struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
1609
1610 /* Happens for the boot cpu */
1611 if (state != CPUHP_AP_ONLINE_IDLE)
1612 return;
1613
1614 cpuhp_ap_update_sync_state(state: SYNC_STATE_ONLINE);
1615
1616 /*
1617 * Unpark the stopper thread before we start the idle loop (and start
1618 * scheduling); this ensures the stopper task is always available.
1619 */
1620 stop_machine_unpark(smp_processor_id());
1621
1622 st->state = CPUHP_AP_ONLINE_IDLE;
1623 complete_ap_thread(st, bringup: true);
1624}
1625
1626/* Requires cpu_add_remove_lock to be held */
1627static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
1628{
1629 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
1630 struct task_struct *idle;
1631 int ret = 0;
1632
1633 cpus_write_lock();
1634
1635 if (!cpu_present(cpu)) {
1636 ret = -EINVAL;
1637 goto out;
1638 }
1639
1640 /*
1641 * The caller of cpu_up() might have raced with another
1642 * caller. Nothing to do.
1643 */
1644 if (st->state >= target)
1645 goto out;
1646
1647 if (st->state == CPUHP_OFFLINE) {
1648 /* Let it fail before we try to bring the cpu up */
1649 idle = idle_thread_get(cpu);
1650 if (IS_ERR(ptr: idle)) {
1651 ret = PTR_ERR(ptr: idle);
1652 goto out;
1653 }
1654
1655 /*
1656 * Reset stale stack state from the last time this CPU was online.
1657 */
1658 scs_task_reset(tsk: idle);
1659 kasan_unpoison_task_stack(task: idle);
1660 }
1661
1662 cpuhp_tasks_frozen = tasks_frozen;
1663
1664 cpuhp_set_state(cpu, st, target);
1665 /*
1666 * If the current CPU state is in the range of the AP hotplug thread,
1667 * then we need to kick the thread once more.
1668 */
1669 if (st->state > CPUHP_BRINGUP_CPU) {
1670 ret = cpuhp_kick_ap_work(cpu);
1671 /*
1672 * The AP side has done the error rollback already. Just
1673 * return the error code..
1674 */
1675 if (ret)
1676 goto out;
1677 }
1678
1679 /*
1680 * Try to reach the target state. We max out on the BP at
1681 * CPUHP_BRINGUP_CPU. After that the AP hotplug thread is
1682 * responsible for bringing it up to the target state.
1683 */
1684 target = min((int)target, CPUHP_BRINGUP_CPU);
1685 ret = cpuhp_up_callbacks(cpu, st, target);
1686out:
1687 cpus_write_unlock();
1688 arch_smt_update();
1689 return ret;
1690}
1691
1692static int cpu_up(unsigned int cpu, enum cpuhp_state target)
1693{
1694 int err = 0;
1695
1696 if (!cpu_possible(cpu)) {
1697 pr_err("can't online cpu %d because it is not configured as may-hotadd at boot time\n",
1698 cpu);
1699 return -EINVAL;
1700 }
1701
1702 err = try_online_node(nid: cpu_to_node(cpu));
1703 if (err)
1704 return err;
1705
1706 cpu_maps_update_begin();
1707
1708 if (cpu_hotplug_disabled) {
1709 err = -EBUSY;
1710 goto out;
1711 }
1712 if (!cpu_bootable(cpu)) {
1713 err = -EPERM;
1714 goto out;
1715 }
1716
1717 err = _cpu_up(cpu, tasks_frozen: 0, target);
1718out:
1719 cpu_maps_update_done();
1720 return err;
1721}
1722
1723/**
1724 * cpu_device_up - Bring up a cpu device
1725 * @dev: Pointer to the cpu device to online
1726 *
1727 * This function is meant to be used by device core cpu subsystem only.
1728 *
1729 * Other subsystems should use add_cpu() instead.
1730 *
1731 * Return: %0 on success or a negative errno code
1732 */
1733int cpu_device_up(struct device *dev)
1734{
1735 return cpu_up(cpu: dev->id, target: CPUHP_ONLINE);
1736}
1737
1738int add_cpu(unsigned int cpu)
1739{
1740 int ret;
1741
1742 lock_device_hotplug();
1743 ret = device_online(dev: get_cpu_device(cpu));
1744 unlock_device_hotplug();
1745
1746 return ret;
1747}
1748EXPORT_SYMBOL_GPL(add_cpu);
1749
1750/**
1751 * bringup_hibernate_cpu - Bring up the CPU that we hibernated on
1752 * @sleep_cpu: The cpu we hibernated on and should be brought up.
1753 *
1754 * On some architectures like arm64, we can hibernate on any CPU, but on
1755 * wake up the CPU we hibernated on might be offline as a side effect of
1756 * using maxcpus= for example.
1757 *
1758 * Return: %0 on success or a negative errno code
1759 */
1760int bringup_hibernate_cpu(unsigned int sleep_cpu)
1761{
1762 int ret;
1763
1764 if (!cpu_online(cpu: sleep_cpu)) {
1765 pr_info("Hibernated on a CPU that is offline! Bringing CPU up.\n");
1766 ret = cpu_up(cpu: sleep_cpu, target: CPUHP_ONLINE);
1767 if (ret) {
1768 pr_err("Failed to bring hibernate-CPU up!\n");
1769 return ret;
1770 }
1771 }
1772 return 0;
1773}
1774
1775static void __init cpuhp_bringup_mask(const struct cpumask *mask, unsigned int ncpus,
1776 enum cpuhp_state target)
1777{
1778 unsigned int cpu;
1779
1780 for_each_cpu(cpu, mask) {
1781 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
1782
1783 if (cpu_up(cpu, target) && can_rollback_cpu(st)) {
1784 /*
1785 * If this failed then cpu_up() might have only
1786 * rolled back to CPUHP_BP_KICK_AP for the final
1787 * online. Clean it up. NOOP if already rolled back.
1788 */
1789 WARN_ON(cpuhp_invoke_callback_range(false, cpu, st, CPUHP_OFFLINE));
1790 }
1791
1792 if (!--ncpus)
1793 break;
1794 }
1795}
1796
1797#ifdef CONFIG_HOTPLUG_PARALLEL
1798static bool __cpuhp_parallel_bringup __ro_after_init = true;
1799
1800static int __init parallel_bringup_parse_param(char *arg)
1801{
1802 return kstrtobool(s: arg, res: &__cpuhp_parallel_bringup);
1803}
1804early_param("cpuhp.parallel", parallel_bringup_parse_param);
1805
1806#ifdef CONFIG_HOTPLUG_SMT
1807static inline bool cpuhp_smt_aware(void)
1808{
1809 return cpu_smt_max_threads > 1;
1810}
1811
1812static inline const struct cpumask *cpuhp_get_primary_thread_mask(void)
1813{
1814 return cpu_primary_thread_mask;
1815}
1816#else
1817static inline bool cpuhp_smt_aware(void)
1818{
1819 return false;
1820}
1821static inline const struct cpumask *cpuhp_get_primary_thread_mask(void)
1822{
1823 return cpu_none_mask;
1824}
1825#endif
1826
1827bool __weak arch_cpuhp_init_parallel_bringup(void)
1828{
1829 return true;
1830}
1831
1832/*
1833 * On architectures which have enabled parallel bringup this invokes all BP
1834 * prepare states for each of the to be onlined APs first. The last state
1835 * sends the startup IPI to the APs. The APs proceed through the low level
1836 * bringup code in parallel and then wait for the control CPU to release
1837 * them one by one for the final onlining procedure.
1838 *
1839 * This avoids waiting for each AP to respond to the startup IPI in
1840 * CPUHP_BRINGUP_CPU.
1841 */
1842static bool __init cpuhp_bringup_cpus_parallel(unsigned int ncpus)
1843{
1844 const struct cpumask *mask = cpu_present_mask;
1845
1846 if (__cpuhp_parallel_bringup)
1847 __cpuhp_parallel_bringup = arch_cpuhp_init_parallel_bringup();
1848 if (!__cpuhp_parallel_bringup)
1849 return false;
1850
1851 if (cpuhp_smt_aware()) {
1852 const struct cpumask *pmask = cpuhp_get_primary_thread_mask();
1853 static struct cpumask tmp_mask __initdata;
1854
1855 /*
1856 * X86 requires to prevent that SMT siblings stopped while
1857 * the primary thread does a microcode update for various
1858 * reasons. Bring the primary threads up first.
1859 */
1860 cpumask_and(dstp: &tmp_mask, src1p: mask, src2p: pmask);
1861 cpuhp_bringup_mask(mask: &tmp_mask, ncpus, target: CPUHP_BP_KICK_AP);
1862 cpuhp_bringup_mask(mask: &tmp_mask, ncpus, target: CPUHP_ONLINE);
1863 /* Account for the online CPUs */
1864 ncpus -= num_online_cpus();
1865 if (!ncpus)
1866 return true;
1867 /* Create the mask for secondary CPUs */
1868 cpumask_andnot(dstp: &tmp_mask, src1p: mask, src2p: pmask);
1869 mask = &tmp_mask;
1870 }
1871
1872 /* Bring the not-yet started CPUs up */
1873 cpuhp_bringup_mask(mask, ncpus, target: CPUHP_BP_KICK_AP);
1874 cpuhp_bringup_mask(mask, ncpus, target: CPUHP_ONLINE);
1875 return true;
1876}
1877#else
1878static inline bool cpuhp_bringup_cpus_parallel(unsigned int ncpus) { return false; }
1879#endif /* CONFIG_HOTPLUG_PARALLEL */
1880
1881void __init bringup_nonboot_cpus(unsigned int max_cpus)
1882{
1883 if (!max_cpus)
1884 return;
1885
1886 /* Try parallel bringup optimization if enabled */
1887 if (cpuhp_bringup_cpus_parallel(ncpus: max_cpus))
1888 return;
1889
1890 /* Full per CPU serialized bringup */
1891 cpuhp_bringup_mask(cpu_present_mask, ncpus: max_cpus, target: CPUHP_ONLINE);
1892}
1893
1894#ifdef CONFIG_PM_SLEEP_SMP
1895static cpumask_var_t frozen_cpus;
1896
1897int freeze_secondary_cpus(int primary)
1898{
1899 int cpu, error = 0;
1900
1901 cpu_maps_update_begin();
1902 if (primary == -1) {
1903 primary = cpumask_first(cpu_online_mask);
1904 if (!housekeeping_cpu(cpu: primary, type: HK_TYPE_TIMER))
1905 primary = housekeeping_any_cpu(type: HK_TYPE_TIMER);
1906 } else {
1907 if (!cpu_online(cpu: primary))
1908 primary = cpumask_first(cpu_online_mask);
1909 }
1910
1911 /*
1912 * We take down all of the non-boot CPUs in one shot to avoid races
1913 * with the userspace trying to use the CPU hotplug at the same time
1914 */
1915 cpumask_clear(dstp: frozen_cpus);
1916
1917 pr_info("Disabling non-boot CPUs ...\n");
1918 for (cpu = nr_cpu_ids - 1; cpu >= 0; cpu--) {
1919 if (!cpu_online(cpu) || cpu == primary)
1920 continue;
1921
1922 if (pm_wakeup_pending()) {
1923 pr_info("Wakeup pending. Abort CPU freeze\n");
1924 error = -EBUSY;
1925 break;
1926 }
1927
1928 trace_suspend_resume(TPS("CPU_OFF"), val: cpu, start: true);
1929 error = _cpu_down(cpu, tasks_frozen: 1, target: CPUHP_OFFLINE);
1930 trace_suspend_resume(TPS("CPU_OFF"), val: cpu, start: false);
1931 if (!error)
1932 cpumask_set_cpu(cpu, dstp: frozen_cpus);
1933 else {
1934 pr_err("Error taking CPU%d down: %d\n", cpu, error);
1935 break;
1936 }
1937 }
1938
1939 if (!error)
1940 BUG_ON(num_online_cpus() > 1);
1941 else
1942 pr_err("Non-boot CPUs are not disabled\n");
1943
1944 /*
1945 * Make sure the CPUs won't be enabled by someone else. We need to do
1946 * this even in case of failure as all freeze_secondary_cpus() users are
1947 * supposed to do thaw_secondary_cpus() on the failure path.
1948 */
1949 cpu_hotplug_disabled++;
1950
1951 cpu_maps_update_done();
1952 return error;
1953}
1954
1955void __weak arch_thaw_secondary_cpus_begin(void)
1956{
1957}
1958
1959void __weak arch_thaw_secondary_cpus_end(void)
1960{
1961}
1962
1963void thaw_secondary_cpus(void)
1964{
1965 int cpu, error;
1966
1967 /* Allow everyone to use the CPU hotplug again */
1968 cpu_maps_update_begin();
1969 __cpu_hotplug_enable();
1970 if (cpumask_empty(srcp: frozen_cpus))
1971 goto out;
1972
1973 pr_info("Enabling non-boot CPUs ...\n");
1974
1975 arch_thaw_secondary_cpus_begin();
1976
1977 for_each_cpu(cpu, frozen_cpus) {
1978 trace_suspend_resume(TPS("CPU_ON"), val: cpu, start: true);
1979 error = _cpu_up(cpu, tasks_frozen: 1, target: CPUHP_ONLINE);
1980 trace_suspend_resume(TPS("CPU_ON"), val: cpu, start: false);
1981 if (!error) {
1982 pr_info("CPU%d is up\n", cpu);
1983 continue;
1984 }
1985 pr_warn("Error taking CPU%d up: %d\n", cpu, error);
1986 }
1987
1988 arch_thaw_secondary_cpus_end();
1989
1990 cpumask_clear(dstp: frozen_cpus);
1991out:
1992 cpu_maps_update_done();
1993}
1994
1995static int __init alloc_frozen_cpus(void)
1996{
1997 if (!alloc_cpumask_var(mask: &frozen_cpus, GFP_KERNEL|__GFP_ZERO))
1998 return -ENOMEM;
1999 return 0;
2000}
2001core_initcall(alloc_frozen_cpus);
2002
2003/*
2004 * When callbacks for CPU hotplug notifications are being executed, we must
2005 * ensure that the state of the system with respect to the tasks being frozen
2006 * or not, as reported by the notification, remains unchanged *throughout the
2007 * duration* of the execution of the callbacks.
2008 * Hence we need to prevent the freezer from racing with regular CPU hotplug.
2009 *
2010 * This synchronization is implemented by mutually excluding regular CPU
2011 * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
2012 * Hibernate notifications.
2013 */
2014static int
2015cpu_hotplug_pm_callback(struct notifier_block *nb,
2016 unsigned long action, void *ptr)
2017{
2018 switch (action) {
2019
2020 case PM_SUSPEND_PREPARE:
2021 case PM_HIBERNATION_PREPARE:
2022 cpu_hotplug_disable();
2023 break;
2024
2025 case PM_POST_SUSPEND:
2026 case PM_POST_HIBERNATION:
2027 cpu_hotplug_enable();
2028 break;
2029
2030 default:
2031 return NOTIFY_DONE;
2032 }
2033
2034 return NOTIFY_OK;
2035}
2036
2037
2038static int __init cpu_hotplug_pm_sync_init(void)
2039{
2040 /*
2041 * cpu_hotplug_pm_callback has higher priority than x86
2042 * bsp_pm_callback which depends on cpu_hotplug_pm_callback
2043 * to disable cpu hotplug to avoid cpu hotplug race.
2044 */
2045 pm_notifier(cpu_hotplug_pm_callback, 0);
2046 return 0;
2047}
2048core_initcall(cpu_hotplug_pm_sync_init);
2049
2050#endif /* CONFIG_PM_SLEEP_SMP */
2051
2052int __boot_cpu_id;
2053
2054#endif /* CONFIG_SMP */
2055
2056/* Boot processor state steps */
2057static struct cpuhp_step cpuhp_hp_states[] = {
2058 [CPUHP_OFFLINE] = {
2059 .name = "offline",
2060 .startup.single = NULL,
2061 .teardown.single = NULL,
2062 },
2063#ifdef CONFIG_SMP
2064 [CPUHP_CREATE_THREADS]= {
2065 .name = "threads:prepare",
2066 .startup.single = smpboot_create_threads,
2067 .teardown.single = NULL,
2068 .cant_stop = true,
2069 },
2070 [CPUHP_RANDOM_PREPARE] = {
2071 .name = "random:prepare",
2072 .startup.single = random_prepare_cpu,
2073 .teardown.single = NULL,
2074 },
2075 [CPUHP_WORKQUEUE_PREP] = {
2076 .name = "workqueue:prepare",
2077 .startup.single = workqueue_prepare_cpu,
2078 .teardown.single = NULL,
2079 },
2080 [CPUHP_HRTIMERS_PREPARE] = {
2081 .name = "hrtimers:prepare",
2082 .startup.single = hrtimers_prepare_cpu,
2083 .teardown.single = NULL,
2084 },
2085 [CPUHP_SMPCFD_PREPARE] = {
2086 .name = "smpcfd:prepare",
2087 .startup.single = smpcfd_prepare_cpu,
2088 .teardown.single = smpcfd_dead_cpu,
2089 },
2090 [CPUHP_RELAY_PREPARE] = {
2091 .name = "relay:prepare",
2092 .startup.single = relay_prepare_cpu,
2093 .teardown.single = NULL,
2094 },
2095 [CPUHP_RCUTREE_PREP] = {
2096 .name = "RCU/tree:prepare",
2097 .startup.single = rcutree_prepare_cpu,
2098 .teardown.single = rcutree_dead_cpu,
2099 },
2100 /*
2101 * On the tear-down path, timers_dead_cpu() must be invoked
2102 * before blk_mq_queue_reinit_notify() from notify_dead(),
2103 * otherwise a RCU stall occurs.
2104 */
2105 [CPUHP_TIMERS_PREPARE] = {
2106 .name = "timers:prepare",
2107 .startup.single = timers_prepare_cpu,
2108 .teardown.single = timers_dead_cpu,
2109 },
2110
2111#ifdef CONFIG_HOTPLUG_SPLIT_STARTUP
2112 /*
2113 * Kicks the AP alive. AP will wait in cpuhp_ap_sync_alive() until
2114 * the next step will release it.
2115 */
2116 [CPUHP_BP_KICK_AP] = {
2117 .name = "cpu:kick_ap",
2118 .startup.single = cpuhp_kick_ap_alive,
2119 },
2120
2121 /*
2122 * Waits for the AP to reach cpuhp_ap_sync_alive() and then
2123 * releases it for the complete bringup.
2124 */
2125 [CPUHP_BRINGUP_CPU] = {
2126 .name = "cpu:bringup",
2127 .startup.single = cpuhp_bringup_ap,
2128 .teardown.single = finish_cpu,
2129 .cant_stop = true,
2130 },
2131#else
2132 /*
2133 * All-in-one CPU bringup state which includes the kick alive.
2134 */
2135 [CPUHP_BRINGUP_CPU] = {
2136 .name = "cpu:bringup",
2137 .startup.single = bringup_cpu,
2138 .teardown.single = finish_cpu,
2139 .cant_stop = true,
2140 },
2141#endif
2142 /* Final state before CPU kills itself */
2143 [CPUHP_AP_IDLE_DEAD] = {
2144 .name = "idle:dead",
2145 },
2146 /*
2147 * Last state before CPU enters the idle loop to die. Transient state
2148 * for synchronization.
2149 */
2150 [CPUHP_AP_OFFLINE] = {
2151 .name = "ap:offline",
2152 .cant_stop = true,
2153 },
2154 /* First state is scheduler control. Interrupts are disabled */
2155 [CPUHP_AP_SCHED_STARTING] = {
2156 .name = "sched:starting",
2157 .startup.single = sched_cpu_starting,
2158 .teardown.single = sched_cpu_dying,
2159 },
2160 [CPUHP_AP_RCUTREE_DYING] = {
2161 .name = "RCU/tree:dying",
2162 .startup.single = NULL,
2163 .teardown.single = rcutree_dying_cpu,
2164 },
2165 [CPUHP_AP_SMPCFD_DYING] = {
2166 .name = "smpcfd:dying",
2167 .startup.single = NULL,
2168 .teardown.single = smpcfd_dying_cpu,
2169 },
2170 [CPUHP_AP_HRTIMERS_DYING] = {
2171 .name = "hrtimers:dying",
2172 .startup.single = hrtimers_cpu_starting,
2173 .teardown.single = hrtimers_cpu_dying,
2174 },
2175 [CPUHP_AP_TICK_DYING] = {
2176 .name = "tick:dying",
2177 .startup.single = NULL,
2178 .teardown.single = tick_cpu_dying,
2179 },
2180 /* Entry state on starting. Interrupts enabled from here on. Transient
2181 * state for synchronsization */
2182 [CPUHP_AP_ONLINE] = {
2183 .name = "ap:online",
2184 },
2185 /*
2186 * Handled on control processor until the plugged processor manages
2187 * this itself.
2188 */
2189 [CPUHP_TEARDOWN_CPU] = {
2190 .name = "cpu:teardown",
2191 .startup.single = NULL,
2192 .teardown.single = takedown_cpu,
2193 .cant_stop = true,
2194 },
2195
2196 [CPUHP_AP_SCHED_WAIT_EMPTY] = {
2197 .name = "sched:waitempty",
2198 .startup.single = NULL,
2199 .teardown.single = sched_cpu_wait_empty,
2200 },
2201
2202 /* Handle smpboot threads park/unpark */
2203 [CPUHP_AP_SMPBOOT_THREADS] = {
2204 .name = "smpboot/threads:online",
2205 .startup.single = smpboot_unpark_threads,
2206 .teardown.single = smpboot_park_threads,
2207 },
2208 [CPUHP_AP_IRQ_AFFINITY_ONLINE] = {
2209 .name = "irq/affinity:online",
2210 .startup.single = irq_affinity_online_cpu,
2211 .teardown.single = NULL,
2212 },
2213 [CPUHP_AP_PERF_ONLINE] = {
2214 .name = "perf:online",
2215 .startup.single = perf_event_init_cpu,
2216 .teardown.single = perf_event_exit_cpu,
2217 },
2218 [CPUHP_AP_WATCHDOG_ONLINE] = {
2219 .name = "lockup_detector:online",
2220 .startup.single = lockup_detector_online_cpu,
2221 .teardown.single = lockup_detector_offline_cpu,
2222 },
2223 [CPUHP_AP_WORKQUEUE_ONLINE] = {
2224 .name = "workqueue:online",
2225 .startup.single = workqueue_online_cpu,
2226 .teardown.single = workqueue_offline_cpu,
2227 },
2228 [CPUHP_AP_RANDOM_ONLINE] = {
2229 .name = "random:online",
2230 .startup.single = random_online_cpu,
2231 .teardown.single = NULL,
2232 },
2233 [CPUHP_AP_RCUTREE_ONLINE] = {
2234 .name = "RCU/tree:online",
2235 .startup.single = rcutree_online_cpu,
2236 .teardown.single = rcutree_offline_cpu,
2237 },
2238#endif
2239 /*
2240 * The dynamically registered state space is here
2241 */
2242
2243#ifdef CONFIG_SMP
2244 /* Last state is scheduler control setting the cpu active */
2245 [CPUHP_AP_ACTIVE] = {
2246 .name = "sched:active",
2247 .startup.single = sched_cpu_activate,
2248 .teardown.single = sched_cpu_deactivate,
2249 },
2250#endif
2251
2252 /* CPU is fully up and running. */
2253 [CPUHP_ONLINE] = {
2254 .name = "online",
2255 .startup.single = NULL,
2256 .teardown.single = NULL,
2257 },
2258};
2259
2260/* Sanity check for callbacks */
2261static int cpuhp_cb_check(enum cpuhp_state state)
2262{
2263 if (state <= CPUHP_OFFLINE || state >= CPUHP_ONLINE)
2264 return -EINVAL;
2265 return 0;
2266}
2267
2268/*
2269 * Returns a free for dynamic slot assignment of the Online state. The states
2270 * are protected by the cpuhp_slot_states mutex and an empty slot is identified
2271 * by having no name assigned.
2272 */
2273static int cpuhp_reserve_state(enum cpuhp_state state)
2274{
2275 enum cpuhp_state i, end;
2276 struct cpuhp_step *step;
2277
2278 switch (state) {
2279 case CPUHP_AP_ONLINE_DYN:
2280 step = cpuhp_hp_states + CPUHP_AP_ONLINE_DYN;
2281 end = CPUHP_AP_ONLINE_DYN_END;
2282 break;
2283 case CPUHP_BP_PREPARE_DYN:
2284 step = cpuhp_hp_states + CPUHP_BP_PREPARE_DYN;
2285 end = CPUHP_BP_PREPARE_DYN_END;
2286 break;
2287 default:
2288 return -EINVAL;
2289 }
2290
2291 for (i = state; i <= end; i++, step++) {
2292 if (!step->name)
2293 return i;
2294 }
2295 WARN(1, "No more dynamic states available for CPU hotplug\n");
2296 return -ENOSPC;
2297}
2298
2299static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name,
2300 int (*startup)(unsigned int cpu),
2301 int (*teardown)(unsigned int cpu),
2302 bool multi_instance)
2303{
2304 /* (Un)Install the callbacks for further cpu hotplug operations */
2305 struct cpuhp_step *sp;
2306 int ret = 0;
2307
2308 /*
2309 * If name is NULL, then the state gets removed.
2310 *
2311 * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
2312 * the first allocation from these dynamic ranges, so the removal
2313 * would trigger a new allocation and clear the wrong (already
2314 * empty) state, leaving the callbacks of the to be cleared state
2315 * dangling, which causes wreckage on the next hotplug operation.
2316 */
2317 if (name && (state == CPUHP_AP_ONLINE_DYN ||
2318 state == CPUHP_BP_PREPARE_DYN)) {
2319 ret = cpuhp_reserve_state(state);
2320 if (ret < 0)
2321 return ret;
2322 state = ret;
2323 }
2324 sp = cpuhp_get_step(state);
2325 if (name && sp->name)
2326 return -EBUSY;
2327
2328 sp->startup.single = startup;
2329 sp->teardown.single = teardown;
2330 sp->name = name;
2331 sp->multi_instance = multi_instance;
2332 INIT_HLIST_HEAD(&sp->list);
2333 return ret;
2334}
2335
2336static void *cpuhp_get_teardown_cb(enum cpuhp_state state)
2337{
2338 return cpuhp_get_step(state)->teardown.single;
2339}
2340
2341/*
2342 * Call the startup/teardown function for a step either on the AP or
2343 * on the current CPU.
2344 */
2345static int cpuhp_issue_call(int cpu, enum cpuhp_state state, bool bringup,
2346 struct hlist_node *node)
2347{
2348 struct cpuhp_step *sp = cpuhp_get_step(state);
2349 int ret;
2350
2351 /*
2352 * If there's nothing to do, we done.
2353 * Relies on the union for multi_instance.
2354 */
2355 if (cpuhp_step_empty(bringup, step: sp))
2356 return 0;
2357 /*
2358 * The non AP bound callbacks can fail on bringup. On teardown
2359 * e.g. module removal we crash for now.
2360 */
2361#ifdef CONFIG_SMP
2362 if (cpuhp_is_ap_state(state))
2363 ret = cpuhp_invoke_ap_callback(cpu, state, bringup, node);
2364 else
2365 ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
2366#else
2367 ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
2368#endif
2369 BUG_ON(ret && !bringup);
2370 return ret;
2371}
2372
2373/*
2374 * Called from __cpuhp_setup_state on a recoverable failure.
2375 *
2376 * Note: The teardown callbacks for rollback are not allowed to fail!
2377 */
2378static void cpuhp_rollback_install(int failedcpu, enum cpuhp_state state,
2379 struct hlist_node *node)
2380{
2381 int cpu;
2382
2383 /* Roll back the already executed steps on the other cpus */
2384 for_each_present_cpu(cpu) {
2385 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
2386 int cpustate = st->state;
2387
2388 if (cpu >= failedcpu)
2389 break;
2390
2391 /* Did we invoke the startup call on that cpu ? */
2392 if (cpustate >= state)
2393 cpuhp_issue_call(cpu, state, bringup: false, node);
2394 }
2395}
2396
2397int __cpuhp_state_add_instance_cpuslocked(enum cpuhp_state state,
2398 struct hlist_node *node,
2399 bool invoke)
2400{
2401 struct cpuhp_step *sp;
2402 int cpu;
2403 int ret;
2404
2405 lockdep_assert_cpus_held();
2406
2407 sp = cpuhp_get_step(state);
2408 if (sp->multi_instance == false)
2409 return -EINVAL;
2410
2411 mutex_lock(lock: &cpuhp_state_mutex);
2412
2413 if (!invoke || !sp->startup.multi)
2414 goto add_node;
2415
2416 /*
2417 * Try to call the startup callback for each present cpu
2418 * depending on the hotplug state of the cpu.
2419 */
2420 for_each_present_cpu(cpu) {
2421 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
2422 int cpustate = st->state;
2423
2424 if (cpustate < state)
2425 continue;
2426
2427 ret = cpuhp_issue_call(cpu, state, bringup: true, node);
2428 if (ret) {
2429 if (sp->teardown.multi)
2430 cpuhp_rollback_install(failedcpu: cpu, state, node);
2431 goto unlock;
2432 }
2433 }
2434add_node:
2435 ret = 0;
2436 hlist_add_head(n: node, h: &sp->list);
2437unlock:
2438 mutex_unlock(lock: &cpuhp_state_mutex);
2439 return ret;
2440}
2441
2442int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node,
2443 bool invoke)
2444{
2445 int ret;
2446
2447 cpus_read_lock();
2448 ret = __cpuhp_state_add_instance_cpuslocked(state, node, invoke);
2449 cpus_read_unlock();
2450 return ret;
2451}
2452EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
2453
2454/**
2455 * __cpuhp_setup_state_cpuslocked - Setup the callbacks for an hotplug machine state
2456 * @state: The state to setup
2457 * @name: Name of the step
2458 * @invoke: If true, the startup function is invoked for cpus where
2459 * cpu state >= @state
2460 * @startup: startup callback function
2461 * @teardown: teardown callback function
2462 * @multi_instance: State is set up for multiple instances which get
2463 * added afterwards.
2464 *
2465 * The caller needs to hold cpus read locked while calling this function.
2466 * Return:
2467 * On success:
2468 * Positive state number if @state is CPUHP_AP_ONLINE_DYN or CPUHP_BP_PREPARE_DYN;
2469 * 0 for all other states
2470 * On failure: proper (negative) error code
2471 */
2472int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state,
2473 const char *name, bool invoke,
2474 int (*startup)(unsigned int cpu),
2475 int (*teardown)(unsigned int cpu),
2476 bool multi_instance)
2477{
2478 int cpu, ret = 0;
2479 bool dynstate;
2480
2481 lockdep_assert_cpus_held();
2482
2483 if (cpuhp_cb_check(state) || !name)
2484 return -EINVAL;
2485
2486 mutex_lock(lock: &cpuhp_state_mutex);
2487
2488 ret = cpuhp_store_callbacks(state, name, startup, teardown,
2489 multi_instance);
2490
2491 dynstate = state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN;
2492 if (ret > 0 && dynstate) {
2493 state = ret;
2494 ret = 0;
2495 }
2496
2497 if (ret || !invoke || !startup)
2498 goto out;
2499
2500 /*
2501 * Try to call the startup callback for each present cpu
2502 * depending on the hotplug state of the cpu.
2503 */
2504 for_each_present_cpu(cpu) {
2505 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
2506 int cpustate = st->state;
2507
2508 if (cpustate < state)
2509 continue;
2510
2511 ret = cpuhp_issue_call(cpu, state, bringup: true, NULL);
2512 if (ret) {
2513 if (teardown)
2514 cpuhp_rollback_install(failedcpu: cpu, state, NULL);
2515 cpuhp_store_callbacks(state, NULL, NULL, NULL, multi_instance: false);
2516 goto out;
2517 }
2518 }
2519out:
2520 mutex_unlock(lock: &cpuhp_state_mutex);
2521 /*
2522 * If the requested state is CPUHP_AP_ONLINE_DYN or CPUHP_BP_PREPARE_DYN,
2523 * return the dynamically allocated state in case of success.
2524 */
2525 if (!ret && dynstate)
2526 return state;
2527 return ret;
2528}
2529EXPORT_SYMBOL(__cpuhp_setup_state_cpuslocked);
2530
2531int __cpuhp_setup_state(enum cpuhp_state state,
2532 const char *name, bool invoke,
2533 int (*startup)(unsigned int cpu),
2534 int (*teardown)(unsigned int cpu),
2535 bool multi_instance)
2536{
2537 int ret;
2538
2539 cpus_read_lock();
2540 ret = __cpuhp_setup_state_cpuslocked(state, name, invoke, startup,
2541 teardown, multi_instance);
2542 cpus_read_unlock();
2543 return ret;
2544}
2545EXPORT_SYMBOL(__cpuhp_setup_state);
2546
2547int __cpuhp_state_remove_instance(enum cpuhp_state state,
2548 struct hlist_node *node, bool invoke)
2549{
2550 struct cpuhp_step *sp = cpuhp_get_step(state);
2551 int cpu;
2552
2553 BUG_ON(cpuhp_cb_check(state));
2554
2555 if (!sp->multi_instance)
2556 return -EINVAL;
2557
2558 cpus_read_lock();
2559 mutex_lock(lock: &cpuhp_state_mutex);
2560
2561 if (!invoke || !cpuhp_get_teardown_cb(state))
2562 goto remove;
2563 /*
2564 * Call the teardown callback for each present cpu depending
2565 * on the hotplug state of the cpu. This function is not
2566 * allowed to fail currently!
2567 */
2568 for_each_present_cpu(cpu) {
2569 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
2570 int cpustate = st->state;
2571
2572 if (cpustate >= state)
2573 cpuhp_issue_call(cpu, state, bringup: false, node);
2574 }
2575
2576remove:
2577 hlist_del(n: node);
2578 mutex_unlock(lock: &cpuhp_state_mutex);
2579 cpus_read_unlock();
2580
2581 return 0;
2582}
2583EXPORT_SYMBOL_GPL(__cpuhp_state_remove_instance);
2584
2585/**
2586 * __cpuhp_remove_state_cpuslocked - Remove the callbacks for an hotplug machine state
2587 * @state: The state to remove
2588 * @invoke: If true, the teardown function is invoked for cpus where
2589 * cpu state >= @state
2590 *
2591 * The caller needs to hold cpus read locked while calling this function.
2592 * The teardown callback is currently not allowed to fail. Think
2593 * about module removal!
2594 */
2595void __cpuhp_remove_state_cpuslocked(enum cpuhp_state state, bool invoke)
2596{
2597 struct cpuhp_step *sp = cpuhp_get_step(state);
2598 int cpu;
2599
2600 BUG_ON(cpuhp_cb_check(state));
2601
2602 lockdep_assert_cpus_held();
2603
2604 mutex_lock(lock: &cpuhp_state_mutex);
2605 if (sp->multi_instance) {
2606 WARN(!hlist_empty(&sp->list),
2607 "Error: Removing state %d which has instances left.\n",
2608 state);
2609 goto remove;
2610 }
2611
2612 if (!invoke || !cpuhp_get_teardown_cb(state))
2613 goto remove;
2614
2615 /*
2616 * Call the teardown callback for each present cpu depending
2617 * on the hotplug state of the cpu. This function is not
2618 * allowed to fail currently!
2619 */
2620 for_each_present_cpu(cpu) {
2621 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
2622 int cpustate = st->state;
2623
2624 if (cpustate >= state)
2625 cpuhp_issue_call(cpu, state, bringup: false, NULL);
2626 }
2627remove:
2628 cpuhp_store_callbacks(state, NULL, NULL, NULL, multi_instance: false);
2629 mutex_unlock(lock: &cpuhp_state_mutex);
2630}
2631EXPORT_SYMBOL(__cpuhp_remove_state_cpuslocked);
2632
2633void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
2634{
2635 cpus_read_lock();
2636 __cpuhp_remove_state_cpuslocked(state, invoke);
2637 cpus_read_unlock();
2638}
2639EXPORT_SYMBOL(__cpuhp_remove_state);
2640
2641#ifdef CONFIG_HOTPLUG_SMT
2642static void cpuhp_offline_cpu_device(unsigned int cpu)
2643{
2644 struct device *dev = get_cpu_device(cpu);
2645
2646 dev->offline = true;
2647 /* Tell user space about the state change */
2648 kobject_uevent(kobj: &dev->kobj, action: KOBJ_OFFLINE);
2649}
2650
2651static void cpuhp_online_cpu_device(unsigned int cpu)
2652{
2653 struct device *dev = get_cpu_device(cpu);
2654
2655 dev->offline = false;
2656 /* Tell user space about the state change */
2657 kobject_uevent(kobj: &dev->kobj, action: KOBJ_ONLINE);
2658}
2659
2660int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
2661{
2662 int cpu, ret = 0;
2663
2664 cpu_maps_update_begin();
2665 for_each_online_cpu(cpu) {
2666 if (topology_is_primary_thread(cpu))
2667 continue;
2668 /*
2669 * Disable can be called with CPU_SMT_ENABLED when changing
2670 * from a higher to lower number of SMT threads per core.
2671 */
2672 if (ctrlval == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu))
2673 continue;
2674 ret = cpu_down_maps_locked(cpu, target: CPUHP_OFFLINE);
2675 if (ret)
2676 break;
2677 /*
2678 * As this needs to hold the cpu maps lock it's impossible
2679 * to call device_offline() because that ends up calling
2680 * cpu_down() which takes cpu maps lock. cpu maps lock
2681 * needs to be held as this might race against in kernel
2682 * abusers of the hotplug machinery (thermal management).
2683 *
2684 * So nothing would update device:offline state. That would
2685 * leave the sysfs entry stale and prevent onlining after
2686 * smt control has been changed to 'off' again. This is
2687 * called under the sysfs hotplug lock, so it is properly
2688 * serialized against the regular offline usage.
2689 */
2690 cpuhp_offline_cpu_device(cpu);
2691 }
2692 if (!ret)
2693 cpu_smt_control = ctrlval;
2694 cpu_maps_update_done();
2695 return ret;
2696}
2697
2698/* Check if the core a CPU belongs to is online */
2699#if !defined(topology_is_core_online)
2700static inline bool topology_is_core_online(unsigned int cpu)
2701{
2702 return true;
2703}
2704#endif
2705
2706int cpuhp_smt_enable(void)
2707{
2708 int cpu, ret = 0;
2709
2710 cpu_maps_update_begin();
2711 cpu_smt_control = CPU_SMT_ENABLED;
2712 for_each_present_cpu(cpu) {
2713 /* Skip online CPUs and CPUs on offline nodes */
2714 if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
2715 continue;
2716 if (!cpu_smt_thread_allowed(cpu) || !topology_is_core_online(cpu))
2717 continue;
2718 ret = _cpu_up(cpu, tasks_frozen: 0, target: CPUHP_ONLINE);
2719 if (ret)
2720 break;
2721 /* See comment in cpuhp_smt_disable() */
2722 cpuhp_online_cpu_device(cpu);
2723 }
2724 cpu_maps_update_done();
2725 return ret;
2726}
2727#endif
2728
2729#if defined(CONFIG_SYSFS) && defined(CONFIG_HOTPLUG_CPU)
2730static ssize_t state_show(struct device *dev,
2731 struct device_attribute *attr, char *buf)
2732{
2733 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
2734
2735 return sprintf(buf, fmt: "%d\n", st->state);
2736}
2737static DEVICE_ATTR_RO(state);
2738
2739static ssize_t target_store(struct device *dev, struct device_attribute *attr,
2740 const char *buf, size_t count)
2741{
2742 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
2743 struct cpuhp_step *sp;
2744 int target, ret;
2745
2746 ret = kstrtoint(s: buf, base: 10, res: &target);
2747 if (ret)
2748 return ret;
2749
2750#ifdef CONFIG_CPU_HOTPLUG_STATE_CONTROL
2751 if (target < CPUHP_OFFLINE || target > CPUHP_ONLINE)
2752 return -EINVAL;
2753#else
2754 if (target != CPUHP_OFFLINE && target != CPUHP_ONLINE)
2755 return -EINVAL;
2756#endif
2757
2758 ret = lock_device_hotplug_sysfs();
2759 if (ret)
2760 return ret;
2761
2762 mutex_lock(lock: &cpuhp_state_mutex);
2763 sp = cpuhp_get_step(state: target);
2764 ret = !sp->name || sp->cant_stop ? -EINVAL : 0;
2765 mutex_unlock(lock: &cpuhp_state_mutex);
2766 if (ret)
2767 goto out;
2768
2769 if (st->state < target)
2770 ret = cpu_up(cpu: dev->id, target);
2771 else if (st->state > target)
2772 ret = cpu_down(cpu: dev->id, target);
2773 else if (WARN_ON(st->target != target))
2774 st->target = target;
2775out:
2776 unlock_device_hotplug();
2777 return ret ? ret : count;
2778}
2779
2780static ssize_t target_show(struct device *dev,
2781 struct device_attribute *attr, char *buf)
2782{
2783 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
2784
2785 return sprintf(buf, fmt: "%d\n", st->target);
2786}
2787static DEVICE_ATTR_RW(target);
2788
2789static ssize_t fail_store(struct device *dev, struct device_attribute *attr,
2790 const char *buf, size_t count)
2791{
2792 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
2793 struct cpuhp_step *sp;
2794 int fail, ret;
2795
2796 ret = kstrtoint(s: buf, base: 10, res: &fail);
2797 if (ret)
2798 return ret;
2799
2800 if (fail == CPUHP_INVALID) {
2801 st->fail = fail;
2802 return count;
2803 }
2804
2805 if (fail < CPUHP_OFFLINE || fail > CPUHP_ONLINE)
2806 return -EINVAL;
2807
2808 /*
2809 * Cannot fail STARTING/DYING callbacks.
2810 */
2811 if (cpuhp_is_atomic_state(state: fail))
2812 return -EINVAL;
2813
2814 /*
2815 * DEAD callbacks cannot fail...
2816 * ... neither can CPUHP_BRINGUP_CPU during hotunplug. The latter
2817 * triggering STARTING callbacks, a failure in this state would
2818 * hinder rollback.
2819 */
2820 if (fail <= CPUHP_BRINGUP_CPU && st->state > CPUHP_BRINGUP_CPU)
2821 return -EINVAL;
2822
2823 /*
2824 * Cannot fail anything that doesn't have callbacks.
2825 */
2826 mutex_lock(lock: &cpuhp_state_mutex);
2827 sp = cpuhp_get_step(state: fail);
2828 if (!sp->startup.single && !sp->teardown.single)
2829 ret = -EINVAL;
2830 mutex_unlock(lock: &cpuhp_state_mutex);
2831 if (ret)
2832 return ret;
2833
2834 st->fail = fail;
2835
2836 return count;
2837}
2838
2839static ssize_t fail_show(struct device *dev,
2840 struct device_attribute *attr, char *buf)
2841{
2842 struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
2843
2844 return sprintf(buf, fmt: "%d\n", st->fail);
2845}
2846
2847static DEVICE_ATTR_RW(fail);
2848
2849static struct attribute *cpuhp_cpu_attrs[] = {
2850 &dev_attr_state.attr,
2851 &dev_attr_target.attr,
2852 &dev_attr_fail.attr,
2853 NULL
2854};
2855
2856static const struct attribute_group cpuhp_cpu_attr_group = {
2857 .attrs = cpuhp_cpu_attrs,
2858 .name = "hotplug",
2859};
2860
2861static ssize_t states_show(struct device *dev,
2862 struct device_attribute *attr, char *buf)
2863{
2864 ssize_t cur, res = 0;
2865 int i;
2866
2867 mutex_lock(lock: &cpuhp_state_mutex);
2868 for (i = CPUHP_OFFLINE; i <= CPUHP_ONLINE; i++) {
2869 struct cpuhp_step *sp = cpuhp_get_step(state: i);
2870
2871 if (sp->name) {
2872 cur = sprintf(buf, fmt: "%3d: %s\n", i, sp->name);
2873 buf += cur;
2874 res += cur;
2875 }
2876 }
2877 mutex_unlock(lock: &cpuhp_state_mutex);
2878 return res;
2879}
2880static DEVICE_ATTR_RO(states);
2881
2882static struct attribute *cpuhp_cpu_root_attrs[] = {
2883 &dev_attr_states.attr,
2884 NULL
2885};
2886
2887static const struct attribute_group cpuhp_cpu_root_attr_group = {
2888 .attrs = cpuhp_cpu_root_attrs,
2889 .name = "hotplug",
2890};
2891
2892#ifdef CONFIG_HOTPLUG_SMT
2893
2894static bool cpu_smt_num_threads_valid(unsigned int threads)
2895{
2896 if (IS_ENABLED(CONFIG_SMT_NUM_THREADS_DYNAMIC))
2897 return threads >= 1 && threads <= cpu_smt_max_threads;
2898 return threads == 1 || threads == cpu_smt_max_threads;
2899}
2900
2901static ssize_t
2902__store_smt_control(struct device *dev, struct device_attribute *attr,
2903 const char *buf, size_t count)
2904{
2905 int ctrlval, ret, num_threads, orig_threads;
2906 bool force_off;
2907
2908 if (cpu_smt_control == CPU_SMT_FORCE_DISABLED)
2909 return -EPERM;
2910
2911 if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
2912 return -ENODEV;
2913
2914 if (sysfs_streq(s1: buf, s2: "on")) {
2915 ctrlval = CPU_SMT_ENABLED;
2916 num_threads = cpu_smt_max_threads;
2917 } else if (sysfs_streq(s1: buf, s2: "off")) {
2918 ctrlval = CPU_SMT_DISABLED;
2919 num_threads = 1;
2920 } else if (sysfs_streq(s1: buf, s2: "forceoff")) {
2921 ctrlval = CPU_SMT_FORCE_DISABLED;
2922 num_threads = 1;
2923 } else if (kstrtoint(s: buf, base: 10, res: &num_threads) == 0) {
2924 if (num_threads == 1)
2925 ctrlval = CPU_SMT_DISABLED;
2926 else if (cpu_smt_num_threads_valid(threads: num_threads))
2927 ctrlval = CPU_SMT_ENABLED;
2928 else
2929 return -EINVAL;
2930 } else {
2931 return -EINVAL;
2932 }
2933
2934 ret = lock_device_hotplug_sysfs();
2935 if (ret)
2936 return ret;
2937
2938 orig_threads = cpu_smt_num_threads;
2939 cpu_smt_num_threads = num_threads;
2940
2941 force_off = ctrlval != cpu_smt_control && ctrlval == CPU_SMT_FORCE_DISABLED;
2942
2943 if (num_threads > orig_threads)
2944 ret = cpuhp_smt_enable();
2945 else if (num_threads < orig_threads || force_off)
2946 ret = cpuhp_smt_disable(ctrlval);
2947
2948 unlock_device_hotplug();
2949 return ret ? ret : count;
2950}
2951
2952#else /* !CONFIG_HOTPLUG_SMT */
2953static ssize_t
2954__store_smt_control(struct device *dev, struct device_attribute *attr,
2955 const char *buf, size_t count)
2956{
2957 return -ENODEV;
2958}
2959#endif /* CONFIG_HOTPLUG_SMT */
2960
2961static const char *smt_states[] = {
2962 [CPU_SMT_ENABLED] = "on",
2963 [CPU_SMT_DISABLED] = "off",
2964 [CPU_SMT_FORCE_DISABLED] = "forceoff",
2965 [CPU_SMT_NOT_SUPPORTED] = "notsupported",
2966 [CPU_SMT_NOT_IMPLEMENTED] = "notimplemented",
2967};
2968
2969static ssize_t control_show(struct device *dev,
2970 struct device_attribute *attr, char *buf)
2971{
2972 const char *state = smt_states[cpu_smt_control];
2973
2974#ifdef CONFIG_HOTPLUG_SMT
2975 /*
2976 * If SMT is enabled but not all threads are enabled then show the
2977 * number of threads. If all threads are enabled show "on". Otherwise
2978 * show the state name.
2979 */
2980 if (cpu_smt_control == CPU_SMT_ENABLED &&
2981 cpu_smt_num_threads != cpu_smt_max_threads)
2982 return sysfs_emit(buf, fmt: "%d\n", cpu_smt_num_threads);
2983#endif
2984
2985 return sysfs_emit(buf, fmt: "%s\n", state);
2986}
2987
2988static ssize_t control_store(struct device *dev, struct device_attribute *attr,
2989 const char *buf, size_t count)
2990{
2991 return __store_smt_control(dev, attr, buf, count);
2992}
2993static DEVICE_ATTR_RW(control);
2994
2995static ssize_t active_show(struct device *dev,
2996 struct device_attribute *attr, char *buf)
2997{
2998 return sysfs_emit(buf, fmt: "%d\n", sched_smt_active());
2999}
3000static DEVICE_ATTR_RO(active);
3001
3002static struct attribute *cpuhp_smt_attrs[] = {
3003 &dev_attr_control.attr,
3004 &dev_attr_active.attr,
3005 NULL
3006};
3007
3008static const struct attribute_group cpuhp_smt_attr_group = {
3009 .attrs = cpuhp_smt_attrs,
3010 .name = "smt",
3011};
3012
3013static int __init cpu_smt_sysfs_init(void)
3014{
3015 struct device *dev_root;
3016 int ret = -ENODEV;
3017
3018 dev_root = bus_get_dev_root(bus: &cpu_subsys);
3019 if (dev_root) {
3020 ret = sysfs_create_group(kobj: &dev_root->kobj, grp: &cpuhp_smt_attr_group);
3021 put_device(dev: dev_root);
3022 }
3023 return ret;
3024}
3025
3026static int __init cpuhp_sysfs_init(void)
3027{
3028 struct device *dev_root;
3029 int cpu, ret;
3030
3031 ret = cpu_smt_sysfs_init();
3032 if (ret)
3033 return ret;
3034
3035 dev_root = bus_get_dev_root(bus: &cpu_subsys);
3036 if (dev_root) {
3037 ret = sysfs_create_group(kobj: &dev_root->kobj, grp: &cpuhp_cpu_root_attr_group);
3038 put_device(dev: dev_root);
3039 if (ret)
3040 return ret;
3041 }
3042
3043 for_each_possible_cpu(cpu) {
3044 struct device *dev = get_cpu_device(cpu);
3045
3046 if (!dev)
3047 continue;
3048 ret = sysfs_create_group(kobj: &dev->kobj, grp: &cpuhp_cpu_attr_group);
3049 if (ret)
3050 return ret;
3051 }
3052 return 0;
3053}
3054device_initcall(cpuhp_sysfs_init);
3055#endif /* CONFIG_SYSFS && CONFIG_HOTPLUG_CPU */
3056
3057/*
3058 * cpu_bit_bitmap[] is a special, "compressed" data structure that
3059 * represents all NR_CPUS bits binary values of 1<<nr.
3060 *
3061 * It is used by cpumask_of() to get a constant address to a CPU
3062 * mask value that has a single bit set only.
3063 */
3064
3065/* cpu_bit_bitmap[0] is empty - so we can back into it */
3066#define MASK_DECLARE_1(x) [x+1][0] = (1UL << (x))
3067#define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
3068#define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
3069#define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
3070
3071const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
3072
3073 MASK_DECLARE_8(0), MASK_DECLARE_8(8),
3074 MASK_DECLARE_8(16), MASK_DECLARE_8(24),
3075#if BITS_PER_LONG > 32
3076 MASK_DECLARE_8(32), MASK_DECLARE_8(40),
3077 MASK_DECLARE_8(48), MASK_DECLARE_8(56),
3078#endif
3079};
3080EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
3081
3082const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
3083EXPORT_SYMBOL(cpu_all_bits);
3084
3085#ifdef CONFIG_INIT_ALL_POSSIBLE
3086struct cpumask __cpu_possible_mask __ro_after_init
3087 = {CPU_BITS_ALL};
3088#else
3089struct cpumask __cpu_possible_mask __ro_after_init;
3090#endif
3091EXPORT_SYMBOL(__cpu_possible_mask);
3092
3093struct cpumask __cpu_online_mask __read_mostly;
3094EXPORT_SYMBOL(__cpu_online_mask);
3095
3096struct cpumask __cpu_enabled_mask __read_mostly;
3097EXPORT_SYMBOL(__cpu_enabled_mask);
3098
3099struct cpumask __cpu_present_mask __read_mostly;
3100EXPORT_SYMBOL(__cpu_present_mask);
3101
3102struct cpumask __cpu_active_mask __read_mostly;
3103EXPORT_SYMBOL(__cpu_active_mask);
3104
3105struct cpumask __cpu_dying_mask __read_mostly;
3106EXPORT_SYMBOL(__cpu_dying_mask);
3107
3108atomic_t __num_online_cpus __read_mostly;
3109EXPORT_SYMBOL(__num_online_cpus);
3110
3111void init_cpu_present(const struct cpumask *src)
3112{
3113 cpumask_copy(dstp: &__cpu_present_mask, srcp: src);
3114}
3115
3116void init_cpu_possible(const struct cpumask *src)
3117{
3118 cpumask_copy(dstp: &__cpu_possible_mask, srcp: src);
3119}
3120
3121void set_cpu_online(unsigned int cpu, bool online)
3122{
3123 /*
3124 * atomic_inc/dec() is required to handle the horrid abuse of this
3125 * function by the reboot and kexec code which invoke it from
3126 * IPI/NMI broadcasts when shutting down CPUs. Invocation from
3127 * regular CPU hotplug is properly serialized.
3128 *
3129 * Note, that the fact that __num_online_cpus is of type atomic_t
3130 * does not protect readers which are not serialized against
3131 * concurrent hotplug operations.
3132 */
3133 if (online) {
3134 if (!cpumask_test_and_set_cpu(cpu, cpumask: &__cpu_online_mask))
3135 atomic_inc(v: &__num_online_cpus);
3136 } else {
3137 if (cpumask_test_and_clear_cpu(cpu, cpumask: &__cpu_online_mask))
3138 atomic_dec(v: &__num_online_cpus);
3139 }
3140}
3141
3142/*
3143 * Activate the first processor.
3144 */
3145void __init boot_cpu_init(void)
3146{
3147 int cpu = smp_processor_id();
3148
3149 /* Mark the boot cpu "present", "online" etc for SMP and UP case */
3150 set_cpu_online(cpu, online: true);
3151 set_cpu_active(cpu, true);
3152 set_cpu_present(cpu, true);
3153 set_cpu_possible(cpu, true);
3154
3155#ifdef CONFIG_SMP
3156 __boot_cpu_id = cpu;
3157#endif
3158}
3159
3160/*
3161 * Must be called _AFTER_ setting up the per_cpu areas
3162 */
3163void __init boot_cpu_hotplug_init(void)
3164{
3165#ifdef CONFIG_SMP
3166 cpumask_set_cpu(smp_processor_id(), dstp: &cpus_booted_once_mask);
3167 atomic_set(this_cpu_ptr(&cpuhp_state.ap_sync_state), i: SYNC_STATE_ONLINE);
3168#endif
3169 this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
3170 this_cpu_write(cpuhp_state.target, CPUHP_ONLINE);
3171}
3172
3173#ifdef CONFIG_CPU_MITIGATIONS
3174/*
3175 * All except the cross-thread attack vector are mitigated by default.
3176 * Cross-thread mitigation often requires disabling SMT which is expensive
3177 * so cross-thread mitigations are only partially enabled by default.
3178 *
3179 * Guest-to-Host and Guest-to-Guest vectors are only needed if KVM support is
3180 * present.
3181 */
3182static bool attack_vectors[NR_CPU_ATTACK_VECTORS] __ro_after_init = {
3183 [CPU_MITIGATE_USER_KERNEL] = true,
3184 [CPU_MITIGATE_USER_USER] = true,
3185 [CPU_MITIGATE_GUEST_HOST] = IS_ENABLED(CONFIG_KVM),
3186 [CPU_MITIGATE_GUEST_GUEST] = IS_ENABLED(CONFIG_KVM),
3187};
3188
3189bool cpu_attack_vector_mitigated(enum cpu_attack_vectors v)
3190{
3191 if (v < NR_CPU_ATTACK_VECTORS)
3192 return attack_vectors[v];
3193
3194 WARN_ONCE(1, "Invalid attack vector %d\n", v);
3195 return false;
3196}
3197
3198/*
3199 * There are 3 global options, 'off', 'auto', 'auto,nosmt'. These may optionally
3200 * be combined with attack-vector disables which follow them.
3201 *
3202 * Examples:
3203 * mitigations=auto,no_user_kernel,no_user_user,no_cross_thread
3204 * mitigations=auto,nosmt,no_guest_host,no_guest_guest
3205 *
3206 * mitigations=off is equivalent to disabling all attack vectors.
3207 */
3208enum cpu_mitigations {
3209 CPU_MITIGATIONS_OFF,
3210 CPU_MITIGATIONS_AUTO,
3211 CPU_MITIGATIONS_AUTO_NOSMT,
3212};
3213
3214enum {
3215 NO_USER_KERNEL,
3216 NO_USER_USER,
3217 NO_GUEST_HOST,
3218 NO_GUEST_GUEST,
3219 NO_CROSS_THREAD,
3220 NR_VECTOR_PARAMS,
3221};
3222
3223enum smt_mitigations smt_mitigations __ro_after_init = SMT_MITIGATIONS_AUTO;
3224static enum cpu_mitigations cpu_mitigations __ro_after_init = CPU_MITIGATIONS_AUTO;
3225
3226static const match_table_t global_mitigations = {
3227 { CPU_MITIGATIONS_AUTO_NOSMT, "auto,nosmt"},
3228 { .token: CPU_MITIGATIONS_AUTO, .pattern: "auto"},
3229 { .token: CPU_MITIGATIONS_OFF, .pattern: "off"},
3230};
3231
3232static const match_table_t vector_mitigations = {
3233 { NO_USER_KERNEL, "no_user_kernel"},
3234 { .token: NO_USER_USER, .pattern: "no_user_user"},
3235 { .token: NO_GUEST_HOST, .pattern: "no_guest_host"},
3236 { .token: NO_GUEST_GUEST, .pattern: "no_guest_guest"},
3237 { .token: NO_CROSS_THREAD, .pattern: "no_cross_thread"},
3238 { .token: NR_VECTOR_PARAMS, NULL},
3239};
3240
3241static int __init mitigations_parse_global_opt(char *arg)
3242{
3243 int i;
3244
3245 for (i = 0; i < ARRAY_SIZE(global_mitigations); i++) {
3246 const char *pattern = global_mitigations[i].pattern;
3247
3248 if (!strncmp(arg, pattern, strlen(pattern))) {
3249 cpu_mitigations = global_mitigations[i].token;
3250 return strlen(pattern);
3251 }
3252 }
3253
3254 return 0;
3255}
3256
3257static int __init mitigations_parse_cmdline(char *arg)
3258{
3259 char *s, *p;
3260 int len;
3261
3262 len = mitigations_parse_global_opt(arg);
3263
3264 if (cpu_mitigations_off()) {
3265 memset(s: attack_vectors, c: 0, n: sizeof(attack_vectors));
3266 smt_mitigations = SMT_MITIGATIONS_OFF;
3267 } else if (cpu_mitigations_auto_nosmt()) {
3268 smt_mitigations = SMT_MITIGATIONS_ON;
3269 }
3270
3271 p = arg + len;
3272
3273 if (!*p)
3274 return 0;
3275
3276 /* Attack vector controls may come after the ',' */
3277 if (*p++ != ',' || !IS_ENABLED(CONFIG_ARCH_HAS_CPU_ATTACK_VECTORS)) {
3278 pr_crit("Unsupported mitigations=%s, system may still be vulnerable\n", arg);
3279 return 0;
3280 }
3281
3282 while ((s = strsep(&p, ",")) != NULL) {
3283 switch (match_token(s, table: vector_mitigations, NULL)) {
3284 case NO_USER_KERNEL:
3285 attack_vectors[CPU_MITIGATE_USER_KERNEL] = false;
3286 break;
3287 case NO_USER_USER:
3288 attack_vectors[CPU_MITIGATE_USER_USER] = false;
3289 break;
3290 case NO_GUEST_HOST:
3291 attack_vectors[CPU_MITIGATE_GUEST_HOST] = false;
3292 break;
3293 case NO_GUEST_GUEST:
3294 attack_vectors[CPU_MITIGATE_GUEST_GUEST] = false;
3295 break;
3296 case NO_CROSS_THREAD:
3297 smt_mitigations = SMT_MITIGATIONS_OFF;
3298 break;
3299 default:
3300 pr_crit("Unsupported mitigations options %s\n", s);
3301 return 0;
3302 }
3303 }
3304
3305 return 0;
3306}
3307
3308/* mitigations=off */
3309bool cpu_mitigations_off(void)
3310{
3311 return cpu_mitigations == CPU_MITIGATIONS_OFF;
3312}
3313EXPORT_SYMBOL_GPL(cpu_mitigations_off);
3314
3315/* mitigations=auto,nosmt */
3316bool cpu_mitigations_auto_nosmt(void)
3317{
3318 return cpu_mitigations == CPU_MITIGATIONS_AUTO_NOSMT;
3319}
3320EXPORT_SYMBOL_GPL(cpu_mitigations_auto_nosmt);
3321#else
3322static int __init mitigations_parse_cmdline(char *arg)
3323{
3324 pr_crit("Kernel compiled without mitigations, ignoring 'mitigations'; system may still be vulnerable\n");
3325 return 0;
3326}
3327#endif
3328early_param("mitigations", mitigations_parse_cmdline);
3329