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1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Copyright (C) 2007 Alan Stern
4 * Copyright (C) IBM Corporation, 2009
5 * Copyright (C) 2009, Frederic Weisbecker <fweisbec@gmail.com>
6 *
7 * Thanks to Ingo Molnar for his many suggestions.
8 *
9 * Authors: Alan Stern <stern@rowland.harvard.edu>
10 * K.Prasad <prasad@linux.vnet.ibm.com>
11 * Frederic Weisbecker <fweisbec@gmail.com>
12 */
13
14/*
15 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
16 * using the CPU's debug registers.
17 * This file contains the arch-independent routines.
18 */
19
20#include <linux/hw_breakpoint.h>
21
22#include <linux/atomic.h>
23#include <linux/bug.h>
24#include <linux/cpu.h>
25#include <linux/export.h>
26#include <linux/init.h>
27#include <linux/irqflags.h>
28#include <linux/kdebug.h>
29#include <linux/kernel.h>
30#include <linux/mutex.h>
31#include <linux/notifier.h>
32#include <linux/percpu-rwsem.h>
33#include <linux/percpu.h>
34#include <linux/rhashtable.h>
35#include <linux/sched.h>
36#include <linux/slab.h>
37
38/*
39 * Datastructure to track the total uses of N slots across tasks or CPUs;
40 * bp_slots_histogram::count[N] is the number of assigned N+1 breakpoint slots.
41 */
42struct bp_slots_histogram {
43#ifdef hw_breakpoint_slots
44 atomic_t count[hw_breakpoint_slots(0)];
45#else
46 atomic_t *count;
47#endif
48};
49
50/*
51 * Per-CPU constraints data.
52 */
53struct bp_cpuinfo {
54 /* Number of pinned CPU breakpoints in a CPU. */
55 unsigned int cpu_pinned;
56 /* Histogram of pinned task breakpoints in a CPU. */
57 struct bp_slots_histogram tsk_pinned;
58};
59
60static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
61
62static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type)
63{
64 return per_cpu_ptr(bp_cpuinfo + type, cpu);
65}
66
67/* Number of pinned CPU breakpoints globally. */
68static struct bp_slots_histogram cpu_pinned[TYPE_MAX];
69/* Number of pinned CPU-independent task breakpoints. */
70static struct bp_slots_histogram tsk_pinned_all[TYPE_MAX];
71
72/* Keep track of the breakpoints attached to tasks */
73static struct rhltable task_bps_ht;
74static const struct rhashtable_params task_bps_ht_params = {
75 .head_offset = offsetof(struct hw_perf_event, bp_list),
76 .key_offset = offsetof(struct hw_perf_event, target),
77 .key_len = sizeof_field(struct hw_perf_event, target),
78 .automatic_shrinking = true,
79};
80
81static bool constraints_initialized __ro_after_init;
82
83/*
84 * Synchronizes accesses to the per-CPU constraints; the locking rules are:
85 *
86 * 1. Atomic updates to bp_cpuinfo::tsk_pinned only require a held read-lock
87 * (due to bp_slots_histogram::count being atomic, no update are lost).
88 *
89 * 2. Holding a write-lock is required for computations that require a
90 * stable snapshot of all bp_cpuinfo::tsk_pinned.
91 *
92 * 3. In all other cases, non-atomic accesses require the appropriately held
93 * lock (read-lock for read-only accesses; write-lock for reads/writes).
94 */
95DEFINE_STATIC_PERCPU_RWSEM(bp_cpuinfo_sem);
96
97/*
98 * Return mutex to serialize accesses to per-task lists in task_bps_ht. Since
99 * rhltable synchronizes concurrent insertions/deletions, independent tasks may
100 * insert/delete concurrently; therefore, a mutex per task is sufficient.
101 *
102 * Uses task_struct::perf_event_mutex, to avoid extending task_struct with a
103 * hw_breakpoint-only mutex, which may be infrequently used. The caveat here is
104 * that hw_breakpoint may contend with per-task perf event list management. The
105 * assumption is that perf usecases involving hw_breakpoints are very unlikely
106 * to result in unnecessary contention.
107 */
108static inline struct mutex *get_task_bps_mutex(struct perf_event *bp)
109{
110 struct task_struct *tsk = bp->hw.target;
111
112 return tsk ? &tsk->perf_event_mutex : NULL;
113}
114
115static struct mutex *bp_constraints_lock(struct perf_event *bp)
116{
117 struct mutex *tsk_mtx = get_task_bps_mutex(bp);
118
119 if (tsk_mtx) {
120 /*
121 * Fully analogous to the perf_try_init_event() nesting
122 * argument in the comment near perf_event_ctx_lock_nested();
123 * this child->perf_event_mutex cannot ever deadlock against
124 * the parent->perf_event_mutex usage from
125 * perf_event_task_{en,dis}able().
126 *
127 * Specifically, inherited events will never occur on
128 * ->perf_event_list.
129 */
130 mutex_lock_nested(tsk_mtx, SINGLE_DEPTH_NESTING);
131 percpu_down_read(&bp_cpuinfo_sem);
132 } else {
133 percpu_down_write(&bp_cpuinfo_sem);
134 }
135
136 return tsk_mtx;
137}
138
139static void bp_constraints_unlock(struct mutex *tsk_mtx)
140{
141 if (tsk_mtx) {
142 percpu_up_read(&bp_cpuinfo_sem);
143 mutex_unlock(tsk_mtx);
144 } else {
145 percpu_up_write(&bp_cpuinfo_sem);
146 }
147}
148
149static bool bp_constraints_is_locked(struct perf_event *bp)
150{
151 struct mutex *tsk_mtx = get_task_bps_mutex(bp);
152
153 return percpu_is_write_locked(&bp_cpuinfo_sem) ||
154 (tsk_mtx ? mutex_is_locked(tsk_mtx) :
155 percpu_is_read_locked(&bp_cpuinfo_sem));
156}
157
158static inline void assert_bp_constraints_lock_held(struct perf_event *bp)
159{
160 struct mutex *tsk_mtx = get_task_bps_mutex(bp);
161
162 if (tsk_mtx)
163 lockdep_assert_held(tsk_mtx);
164 lockdep_assert_held(&bp_cpuinfo_sem);
165}
166
167#ifdef hw_breakpoint_slots
168/*
169 * Number of breakpoint slots is constant, and the same for all types.
170 */
171static_assert(hw_breakpoint_slots(TYPE_INST) == hw_breakpoint_slots(TYPE_DATA));
172static inline int hw_breakpoint_slots_cached(int type) { return hw_breakpoint_slots(type); }
173static inline int init_breakpoint_slots(void) { return 0; }
174#else
175/*
176 * Dynamic number of breakpoint slots.
177 */
178static int __nr_bp_slots[TYPE_MAX] __ro_after_init;
179
180static inline int hw_breakpoint_slots_cached(int type)
181{
182 return __nr_bp_slots[type];
183}
184
185static __init bool
186bp_slots_histogram_alloc(struct bp_slots_histogram *hist, enum bp_type_idx type)
187{
188 hist->count = kcalloc(hw_breakpoint_slots_cached(type), sizeof(*hist->count), GFP_KERNEL);
189 return hist->count;
190}
191
192static __init void bp_slots_histogram_free(struct bp_slots_histogram *hist)
193{
194 kfree(hist->count);
195}
196
197static __init int init_breakpoint_slots(void)
198{
199 int i, cpu, err_cpu;
200
201 for (i = 0; i < TYPE_MAX; i++)
202 __nr_bp_slots[i] = hw_breakpoint_slots(i);
203
204 for_each_possible_cpu(cpu) {
205 for (i = 0; i < TYPE_MAX; i++) {
206 struct bp_cpuinfo *info = get_bp_info(cpu, i);
207
208 if (!bp_slots_histogram_alloc(&info->tsk_pinned, i))
209 goto err;
210 }
211 }
212 for (i = 0; i < TYPE_MAX; i++) {
213 if (!bp_slots_histogram_alloc(&cpu_pinned[i], i))
214 goto err;
215 if (!bp_slots_histogram_alloc(&tsk_pinned_all[i], i))
216 goto err;
217 }
218
219 return 0;
220err:
221 for_each_possible_cpu(err_cpu) {
222 for (i = 0; i < TYPE_MAX; i++)
223 bp_slots_histogram_free(&get_bp_info(err_cpu, i)->tsk_pinned);
224 if (err_cpu == cpu)
225 break;
226 }
227 for (i = 0; i < TYPE_MAX; i++) {
228 bp_slots_histogram_free(&cpu_pinned[i]);
229 bp_slots_histogram_free(&tsk_pinned_all[i]);
230 }
231
232 return -ENOMEM;
233}
234#endif
235
236static inline void
237bp_slots_histogram_add(struct bp_slots_histogram *hist, int old, int val)
238{
239 const int old_idx = old - 1;
240 const int new_idx = old_idx + val;
241
242 if (old_idx >= 0)
243 WARN_ON(atomic_dec_return_relaxed(&hist->count[old_idx]) < 0);
244 if (new_idx >= 0)
245 WARN_ON(atomic_inc_return_relaxed(&hist->count[new_idx]) < 0);
246}
247
248static int
249bp_slots_histogram_max(struct bp_slots_histogram *hist, enum bp_type_idx type)
250{
251 for (int i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) {
252 const int count = atomic_read(&hist->count[i]);
253
254 /* Catch unexpected writers; we want a stable snapshot. */
255 ASSERT_EXCLUSIVE_WRITER(hist->count[i]);
256 if (count > 0)
257 return i + 1;
258 WARN(count < 0, "inconsistent breakpoint slots histogram");
259 }
260
261 return 0;
262}
263
264static int
265bp_slots_histogram_max_merge(struct bp_slots_histogram *hist1, struct bp_slots_histogram *hist2,
266 enum bp_type_idx type)
267{
268 for (int i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) {
269 const int count1 = atomic_read(&hist1->count[i]);
270 const int count2 = atomic_read(&hist2->count[i]);
271
272 /* Catch unexpected writers; we want a stable snapshot. */
273 ASSERT_EXCLUSIVE_WRITER(hist1->count[i]);
274 ASSERT_EXCLUSIVE_WRITER(hist2->count[i]);
275 if (count1 + count2 > 0)
276 return i + 1;
277 WARN(count1 < 0, "inconsistent breakpoint slots histogram");
278 WARN(count2 < 0, "inconsistent breakpoint slots histogram");
279 }
280
281 return 0;
282}
283
284#ifndef hw_breakpoint_weight
285static inline int hw_breakpoint_weight(struct perf_event *bp)
286{
287 return 1;
288}
289#endif
290
291static inline enum bp_type_idx find_slot_idx(u64 bp_type)
292{
293 if (bp_type & HW_BREAKPOINT_RW)
294 return TYPE_DATA;
295
296 return TYPE_INST;
297}
298
299/*
300 * Return the maximum number of pinned breakpoints a task has in this CPU.
301 */
302static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
303{
304 struct bp_slots_histogram *tsk_pinned = &get_bp_info(cpu, type)->tsk_pinned;
305
306 /*
307 * At this point we want to have acquired the bp_cpuinfo_sem as a
308 * writer to ensure that there are no concurrent writers in
309 * toggle_bp_task_slot() to tsk_pinned, and we get a stable snapshot.
310 */
311 lockdep_assert_held_write(&bp_cpuinfo_sem);
312 return bp_slots_histogram_max_merge(tsk_pinned, &tsk_pinned_all[type], type);
313}
314
315/*
316 * Count the number of breakpoints of the same type and same task.
317 * The given event must be not on the list.
318 *
319 * If @cpu is -1, but the result of task_bp_pinned() is not CPU-independent,
320 * returns a negative value.
321 */
322static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
323{
324 struct rhlist_head *head, *pos;
325 struct perf_event *iter;
326 int count = 0;
327
328 /*
329 * We need a stable snapshot of the per-task breakpoint list.
330 */
331 assert_bp_constraints_lock_held(bp);
332
333 rcu_read_lock();
334 head = rhltable_lookup(&task_bps_ht, &bp->hw.target, task_bps_ht_params);
335 if (!head)
336 goto out;
337
338 rhl_for_each_entry_rcu(iter, pos, head, hw.bp_list) {
339 if (find_slot_idx(iter->attr.bp_type) != type)
340 continue;
341
342 if (iter->cpu >= 0) {
343 if (cpu == -1) {
344 count = -1;
345 goto out;
346 } else if (cpu != iter->cpu)
347 continue;
348 }
349
350 count += hw_breakpoint_weight(iter);
351 }
352
353out:
354 rcu_read_unlock();
355 return count;
356}
357
358static const struct cpumask *cpumask_of_bp(struct perf_event *bp)
359{
360 if (bp->cpu >= 0)
361 return cpumask_of(bp->cpu);
362 return cpu_possible_mask;
363}
364
365/*
366 * Returns the max pinned breakpoint slots in a given
367 * CPU (cpu > -1) or across all of them (cpu = -1).
368 */
369static int
370max_bp_pinned_slots(struct perf_event *bp, enum bp_type_idx type)
371{
372 const struct cpumask *cpumask = cpumask_of_bp(bp);
373 int pinned_slots = 0;
374 int cpu;
375
376 if (bp->hw.target && bp->cpu < 0) {
377 int max_pinned = task_bp_pinned(-1, bp, type);
378
379 if (max_pinned >= 0) {
380 /*
381 * Fast path: task_bp_pinned() is CPU-independent and
382 * returns the same value for any CPU.
383 */
384 max_pinned += bp_slots_histogram_max(&cpu_pinned[type], type);
385 return max_pinned;
386 }
387 }
388
389 for_each_cpu(cpu, cpumask) {
390 struct bp_cpuinfo *info = get_bp_info(cpu, type);
391 int nr;
392
393 nr = info->cpu_pinned;
394 if (!bp->hw.target)
395 nr += max_task_bp_pinned(cpu, type);
396 else
397 nr += task_bp_pinned(cpu, bp, type);
398
399 pinned_slots = max(nr, pinned_slots);
400 }
401
402 return pinned_slots;
403}
404
405/*
406 * Add/remove the given breakpoint in our constraint table
407 */
408static int
409toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type, int weight)
410{
411 int cpu, next_tsk_pinned;
412
413 if (!enable)
414 weight = -weight;
415
416 if (!bp->hw.target) {
417 /*
418 * Update the pinned CPU slots, in per-CPU bp_cpuinfo and in the
419 * global histogram.
420 */
421 struct bp_cpuinfo *info = get_bp_info(bp->cpu, type);
422
423 lockdep_assert_held_write(&bp_cpuinfo_sem);
424 bp_slots_histogram_add(&cpu_pinned[type], info->cpu_pinned, weight);
425 info->cpu_pinned += weight;
426 return 0;
427 }
428
429 /*
430 * If bp->hw.target, tsk_pinned is only modified, but not used
431 * otherwise. We can permit concurrent updates as long as there are no
432 * other uses: having acquired bp_cpuinfo_sem as a reader allows
433 * concurrent updates here. Uses of tsk_pinned will require acquiring
434 * bp_cpuinfo_sem as a writer to stabilize tsk_pinned's value.
435 */
436 lockdep_assert_held_read(&bp_cpuinfo_sem);
437
438 /*
439 * Update the pinned task slots, in per-CPU bp_cpuinfo and in the global
440 * histogram. We need to take care of 4 cases:
441 *
442 * 1. This breakpoint targets all CPUs (cpu < 0), and there may only
443 * exist other task breakpoints targeting all CPUs. In this case we
444 * can simply update the global slots histogram.
445 *
446 * 2. This breakpoint targets a specific CPU (cpu >= 0), but there may
447 * only exist other task breakpoints targeting all CPUs.
448 *
449 * a. On enable: remove the existing breakpoints from the global
450 * slots histogram and use the per-CPU histogram.
451 *
452 * b. On disable: re-insert the existing breakpoints into the global
453 * slots histogram and remove from per-CPU histogram.
454 *
455 * 3. Some other existing task breakpoints target specific CPUs. Only
456 * update the per-CPU slots histogram.
457 */
458
459 if (!enable) {
460 /*
461 * Remove before updating histograms so we can determine if this
462 * was the last task breakpoint for a specific CPU.
463 */
464 int ret = rhltable_remove(&task_bps_ht, &bp->hw.bp_list, task_bps_ht_params);
465
466 if (ret)
467 return ret;
468 }
469 /*
470 * Note: If !enable, next_tsk_pinned will not count the to-be-removed breakpoint.
471 */
472 next_tsk_pinned = task_bp_pinned(-1, bp, type);
473
474 if (next_tsk_pinned >= 0) {
475 if (bp->cpu < 0) { /* Case 1: fast path */
476 if (!enable)
477 next_tsk_pinned += hw_breakpoint_weight(bp);
478 bp_slots_histogram_add(&tsk_pinned_all[type], next_tsk_pinned, weight);
479 } else if (enable) { /* Case 2.a: slow path */
480 /* Add existing to per-CPU histograms. */
481 for_each_possible_cpu(cpu) {
482 bp_slots_histogram_add(&get_bp_info(cpu, type)->tsk_pinned,
483 0, next_tsk_pinned);
484 }
485 /* Add this first CPU-pinned task breakpoint. */
486 bp_slots_histogram_add(&get_bp_info(bp->cpu, type)->tsk_pinned,
487 next_tsk_pinned, weight);
488 /* Rebalance global task pinned histogram. */
489 bp_slots_histogram_add(&tsk_pinned_all[type], next_tsk_pinned,
490 -next_tsk_pinned);
491 } else { /* Case 2.b: slow path */
492 /* Remove this last CPU-pinned task breakpoint. */
493 bp_slots_histogram_add(&get_bp_info(bp->cpu, type)->tsk_pinned,
494 next_tsk_pinned + hw_breakpoint_weight(bp), weight);
495 /* Remove all from per-CPU histograms. */
496 for_each_possible_cpu(cpu) {
497 bp_slots_histogram_add(&get_bp_info(cpu, type)->tsk_pinned,
498 next_tsk_pinned, -next_tsk_pinned);
499 }
500 /* Rebalance global task pinned histogram. */
501 bp_slots_histogram_add(&tsk_pinned_all[type], 0, next_tsk_pinned);
502 }
503 } else { /* Case 3: slow path */
504 const struct cpumask *cpumask = cpumask_of_bp(bp);
505
506 for_each_cpu(cpu, cpumask) {
507 next_tsk_pinned = task_bp_pinned(cpu, bp, type);
508 if (!enable)
509 next_tsk_pinned += hw_breakpoint_weight(bp);
510 bp_slots_histogram_add(&get_bp_info(cpu, type)->tsk_pinned,
511 next_tsk_pinned, weight);
512 }
513 }
514
515 /*
516 * Readers want a stable snapshot of the per-task breakpoint list.
517 */
518 assert_bp_constraints_lock_held(bp);
519
520 if (enable)
521 return rhltable_insert(&task_bps_ht, &bp->hw.bp_list, task_bps_ht_params);
522
523 return 0;
524}
525
526__weak int arch_reserve_bp_slot(struct perf_event *bp)
527{
528 return 0;
529}
530
531__weak void arch_release_bp_slot(struct perf_event *bp)
532{
533}
534
535/*
536 * Function to perform processor-specific cleanup during unregistration
537 */
538__weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
539{
540 /*
541 * A weak stub function here for those archs that don't define
542 * it inside arch/.../kernel/hw_breakpoint.c
543 */
544}
545
546/*
547 * Constraints to check before allowing this new breakpoint counter.
548 *
549 * Note: Flexible breakpoints are currently unimplemented, but outlined in the
550 * below algorithm for completeness. The implementation treats flexible as
551 * pinned due to no guarantee that we currently always schedule flexible events
552 * before a pinned event in a same CPU.
553 *
554 * == Non-pinned counter == (Considered as pinned for now)
555 *
556 * - If attached to a single cpu, check:
557 *
558 * (per_cpu(info->flexible, cpu) || (per_cpu(info->cpu_pinned, cpu)
559 * + max(per_cpu(info->tsk_pinned, cpu)))) < HBP_NUM
560 *
561 * -> If there are already non-pinned counters in this cpu, it means
562 * there is already a free slot for them.
563 * Otherwise, we check that the maximum number of per task
564 * breakpoints (for this cpu) plus the number of per cpu breakpoint
565 * (for this cpu) doesn't cover every registers.
566 *
567 * - If attached to every cpus, check:
568 *
569 * (per_cpu(info->flexible, *) || (max(per_cpu(info->cpu_pinned, *))
570 * + max(per_cpu(info->tsk_pinned, *)))) < HBP_NUM
571 *
572 * -> This is roughly the same, except we check the number of per cpu
573 * bp for every cpu and we keep the max one. Same for the per tasks
574 * breakpoints.
575 *
576 *
577 * == Pinned counter ==
578 *
579 * - If attached to a single cpu, check:
580 *
581 * ((per_cpu(info->flexible, cpu) > 1) + per_cpu(info->cpu_pinned, cpu)
582 * + max(per_cpu(info->tsk_pinned, cpu))) < HBP_NUM
583 *
584 * -> Same checks as before. But now the info->flexible, if any, must keep
585 * one register at least (or they will never be fed).
586 *
587 * - If attached to every cpus, check:
588 *
589 * ((per_cpu(info->flexible, *) > 1) + max(per_cpu(info->cpu_pinned, *))
590 * + max(per_cpu(info->tsk_pinned, *))) < HBP_NUM
591 */
592static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
593{
594 enum bp_type_idx type;
595 int max_pinned_slots;
596 int weight;
597 int ret;
598
599 /* We couldn't initialize breakpoint constraints on boot */
600 if (!constraints_initialized)
601 return -ENOMEM;
602
603 /* Basic checks */
604 if (bp_type == HW_BREAKPOINT_EMPTY ||
605 bp_type == HW_BREAKPOINT_INVALID)
606 return -EINVAL;
607
608 type = find_slot_idx(bp_type);
609 weight = hw_breakpoint_weight(bp);
610
611 /* Check if this new breakpoint can be satisfied across all CPUs. */
612 max_pinned_slots = max_bp_pinned_slots(bp, type) + weight;
613 if (max_pinned_slots > hw_breakpoint_slots_cached(type))
614 return -ENOSPC;
615
616 ret = arch_reserve_bp_slot(bp);
617 if (ret)
618 return ret;
619
620 return toggle_bp_slot(bp, true, type, weight);
621}
622
623int reserve_bp_slot(struct perf_event *bp)
624{
625 struct mutex *mtx = bp_constraints_lock(bp);
626 int ret = __reserve_bp_slot(bp, bp->attr.bp_type);
627
628 bp_constraints_unlock(mtx);
629 return ret;
630}
631
632static void __release_bp_slot(struct perf_event *bp, u64 bp_type)
633{
634 enum bp_type_idx type;
635 int weight;
636
637 arch_release_bp_slot(bp);
638
639 type = find_slot_idx(bp_type);
640 weight = hw_breakpoint_weight(bp);
641 WARN_ON(toggle_bp_slot(bp, false, type, weight));
642}
643
644void release_bp_slot(struct perf_event *bp)
645{
646 struct mutex *mtx = bp_constraints_lock(bp);
647
648 arch_unregister_hw_breakpoint(bp);
649 __release_bp_slot(bp, bp->attr.bp_type);
650 bp_constraints_unlock(mtx);
651}
652
653static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
654{
655 int err;
656
657 __release_bp_slot(bp, old_type);
658
659 err = __reserve_bp_slot(bp, new_type);
660 if (err) {
661 /*
662 * Reserve the old_type slot back in case
663 * there's no space for the new type.
664 *
665 * This must succeed, because we just released
666 * the old_type slot in the __release_bp_slot
667 * call above. If not, something is broken.
668 */
669 WARN_ON(__reserve_bp_slot(bp, old_type));
670 }
671
672 return err;
673}
674
675static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
676{
677 struct mutex *mtx = bp_constraints_lock(bp);
678 int ret = __modify_bp_slot(bp, old_type, new_type);
679
680 bp_constraints_unlock(mtx);
681 return ret;
682}
683
684/*
685 * Allow the kernel debugger to reserve breakpoint slots without
686 * taking a lock using the dbg_* variant of for the reserve and
687 * release breakpoint slots.
688 */
689int dbg_reserve_bp_slot(struct perf_event *bp)
690{
691 int ret;
692
693 if (bp_constraints_is_locked(bp))
694 return -1;
695
696 /* Locks aren't held; disable lockdep assert checking. */
697 lockdep_off();
698 ret = __reserve_bp_slot(bp, bp->attr.bp_type);
699 lockdep_on();
700
701 return ret;
702}
703
704int dbg_release_bp_slot(struct perf_event *bp)
705{
706 if (bp_constraints_is_locked(bp))
707 return -1;
708
709 /* Locks aren't held; disable lockdep assert checking. */
710 lockdep_off();
711 __release_bp_slot(bp, bp->attr.bp_type);
712 lockdep_on();
713
714 return 0;
715}
716
717static int hw_breakpoint_parse(struct perf_event *bp,
718 const struct perf_event_attr *attr,
719 struct arch_hw_breakpoint *hw)
720{
721 int err;
722
723 err = hw_breakpoint_arch_parse(bp, attr, hw);
724 if (err)
725 return err;
726
727 if (arch_check_bp_in_kernelspace(hw)) {
728 if (attr->exclude_kernel)
729 return -EINVAL;
730 /*
731 * Don't let unprivileged users set a breakpoint in the trap
732 * path to avoid trap recursion attacks.
733 */
734 if (!capable(CAP_SYS_ADMIN))
735 return -EPERM;
736 }
737
738 return 0;
739}
740
741int register_perf_hw_breakpoint(struct perf_event *bp)
742{
743 struct arch_hw_breakpoint hw = { };
744 int err;
745
746 err = reserve_bp_slot(bp);
747 if (err)
748 return err;
749
750 err = hw_breakpoint_parse(bp, &bp->attr, &hw);
751 if (err) {
752 release_bp_slot(bp);
753 return err;
754 }
755
756 bp->hw.info = hw;
757
758 return 0;
759}
760
761/**
762 * register_user_hw_breakpoint - register a hardware breakpoint for user space
763 * @attr: breakpoint attributes
764 * @triggered: callback to trigger when we hit the breakpoint
765 * @context: context data could be used in the triggered callback
766 * @tsk: pointer to 'task_struct' of the process to which the address belongs
767 */
768struct perf_event *
769register_user_hw_breakpoint(struct perf_event_attr *attr,
770 perf_overflow_handler_t triggered,
771 void *context,
772 struct task_struct *tsk)
773{
774 return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
775 context);
776}
777EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
778
779static void hw_breakpoint_copy_attr(struct perf_event_attr *to,
780 struct perf_event_attr *from)
781{
782 to->bp_addr = from->bp_addr;
783 to->bp_type = from->bp_type;
784 to->bp_len = from->bp_len;
785 to->disabled = from->disabled;
786}
787
788int
789modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
790 bool check)
791{
792 struct arch_hw_breakpoint hw = { };
793 int err;
794
795 err = hw_breakpoint_parse(bp, attr, &hw);
796 if (err)
797 return err;
798
799 if (check) {
800 struct perf_event_attr old_attr;
801
802 old_attr = bp->attr;
803 hw_breakpoint_copy_attr(&old_attr, attr);
804 if (memcmp(&old_attr, attr, sizeof(*attr)))
805 return -EINVAL;
806 }
807
808 if (bp->attr.bp_type != attr->bp_type) {
809 err = modify_bp_slot(bp, bp->attr.bp_type, attr->bp_type);
810 if (err)
811 return err;
812 }
813
814 hw_breakpoint_copy_attr(&bp->attr, attr);
815 bp->hw.info = hw;
816
817 return 0;
818}
819
820/**
821 * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
822 * @bp: the breakpoint structure to modify
823 * @attr: new breakpoint attributes
824 */
825int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
826{
827 int err;
828
829 /*
830 * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
831 * will not be possible to raise IPIs that invoke __perf_event_disable.
832 * So call the function directly after making sure we are targeting the
833 * current task.
834 */
835 if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
836 perf_event_disable_local(bp);
837 else
838 perf_event_disable(bp);
839
840 err = modify_user_hw_breakpoint_check(bp, attr, false);
841
842 if (!bp->attr.disabled)
843 perf_event_enable(bp);
844
845 return err;
846}
847EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
848
849/**
850 * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
851 * @bp: the breakpoint structure to unregister
852 */
853void unregister_hw_breakpoint(struct perf_event *bp)
854{
855 if (!bp)
856 return;
857 perf_event_release_kernel(bp);
858}
859EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
860
861/**
862 * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
863 * @attr: breakpoint attributes
864 * @triggered: callback to trigger when we hit the breakpoint
865 * @context: context data could be used in the triggered callback
866 *
867 * @return a set of per_cpu pointers to perf events
868 */
869struct perf_event * __percpu *
870register_wide_hw_breakpoint(struct perf_event_attr *attr,
871 perf_overflow_handler_t triggered,
872 void *context)
873{
874 struct perf_event * __percpu *cpu_events, *bp;
875 long err = 0;
876 int cpu;
877
878 cpu_events = alloc_percpu(typeof(*cpu_events));
879 if (!cpu_events)
880 return (void __percpu __force *)ERR_PTR(-ENOMEM);
881
882 cpus_read_lock();
883 for_each_online_cpu(cpu) {
884 bp = perf_event_create_kernel_counter(attr, cpu, NULL,
885 triggered, context);
886 if (IS_ERR(bp)) {
887 err = PTR_ERR(bp);
888 break;
889 }
890
891 per_cpu(*cpu_events, cpu) = bp;
892 }
893 cpus_read_unlock();
894
895 if (likely(!err))
896 return cpu_events;
897
898 unregister_wide_hw_breakpoint(cpu_events);
899 return (void __percpu __force *)ERR_PTR(err);
900}
901EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
902
903/**
904 * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
905 * @cpu_events: the per cpu set of events to unregister
906 */
907void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
908{
909 int cpu;
910
911 for_each_possible_cpu(cpu)
912 unregister_hw_breakpoint(per_cpu(*cpu_events, cpu));
913
914 free_percpu(cpu_events);
915}
916EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
917
918/**
919 * hw_breakpoint_is_used - check if breakpoints are currently used
920 *
921 * Returns: true if breakpoints are used, false otherwise.
922 */
923bool hw_breakpoint_is_used(void)
924{
925 int cpu;
926
927 if (!constraints_initialized)
928 return false;
929
930 for_each_possible_cpu(cpu) {
931 for (int type = 0; type < TYPE_MAX; ++type) {
932 struct bp_cpuinfo *info = get_bp_info(cpu, type);
933
934 if (info->cpu_pinned)
935 return true;
936
937 for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) {
938 if (atomic_read(&info->tsk_pinned.count[slot]))
939 return true;
940 }
941 }
942 }
943
944 for (int type = 0; type < TYPE_MAX; ++type) {
945 for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) {
946 /*
947 * Warn, because if there are CPU pinned counters,
948 * should never get here; bp_cpuinfo::cpu_pinned should
949 * be consistent with the global cpu_pinned histogram.
950 */
951 if (WARN_ON(atomic_read(&cpu_pinned[type].count[slot])))
952 return true;
953
954 if (atomic_read(&tsk_pinned_all[type].count[slot]))
955 return true;
956 }
957 }
958
959 return false;
960}
961
962static struct notifier_block hw_breakpoint_exceptions_nb = {
963 .notifier_call = hw_breakpoint_exceptions_notify,
964 /* we need to be notified first */
965 .priority = 0x7fffffff
966};
967
968static void bp_perf_event_destroy(struct perf_event *event)
969{
970 release_bp_slot(event);
971}
972
973static int hw_breakpoint_event_init(struct perf_event *bp)
974{
975 int err;
976
977 if (bp->attr.type != PERF_TYPE_BREAKPOINT)
978 return -ENOENT;
979
980 /*
981 * no branch sampling for breakpoint events
982 */
983 if (has_branch_stack(bp))
984 return -EOPNOTSUPP;
985
986 err = register_perf_hw_breakpoint(bp);
987 if (err)
988 return err;
989
990 bp->destroy = bp_perf_event_destroy;
991
992 return 0;
993}
994
995static int hw_breakpoint_add(struct perf_event *bp, int flags)
996{
997 if (!(flags & PERF_EF_START))
998 bp->hw.state = PERF_HES_STOPPED;
999
1000 if (is_sampling_event(bp)) {
1001 bp->hw.last_period = bp->hw.sample_period;
1002 perf_swevent_set_period(bp);
1003 }
1004
1005 return arch_install_hw_breakpoint(bp);
1006}
1007
1008static void hw_breakpoint_del(struct perf_event *bp, int flags)
1009{
1010 arch_uninstall_hw_breakpoint(bp);
1011}
1012
1013static void hw_breakpoint_start(struct perf_event *bp, int flags)
1014{
1015 bp->hw.state = 0;
1016}
1017
1018static void hw_breakpoint_stop(struct perf_event *bp, int flags)
1019{
1020 bp->hw.state = PERF_HES_STOPPED;
1021}
1022
1023static struct pmu perf_breakpoint = {
1024 .task_ctx_nr = perf_sw_context, /* could eventually get its own */
1025
1026 .event_init = hw_breakpoint_event_init,
1027 .add = hw_breakpoint_add,
1028 .del = hw_breakpoint_del,
1029 .start = hw_breakpoint_start,
1030 .stop = hw_breakpoint_stop,
1031 .read = hw_breakpoint_pmu_read,
1032};
1033
1034int __init init_hw_breakpoint(void)
1035{
1036 int ret;
1037
1038 ret = rhltable_init(&task_bps_ht, &task_bps_ht_params);
1039 if (ret)
1040 return ret;
1041
1042 ret = init_breakpoint_slots();
1043 if (ret)
1044 return ret;
1045
1046 constraints_initialized = true;
1047
1048 perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
1049
1050 return register_die_notifier(&hw_breakpoint_exceptions_nb);
1051}
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Copyright (C) 2007 Alan Stern
4 * Copyright (C) IBM Corporation, 2009
5 * Copyright (C) 2009, Frederic Weisbecker <fweisbec@gmail.com>
6 *
7 * Thanks to Ingo Molnar for his many suggestions.
8 *
9 * Authors: Alan Stern <stern@rowland.harvard.edu>
10 * K.Prasad <prasad@linux.vnet.ibm.com>
11 * Frederic Weisbecker <fweisbec@gmail.com>
12 */
13
14/*
15 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
16 * using the CPU's debug registers.
17 * This file contains the arch-independent routines.
18 */
19
20#include <linux/irqflags.h>
21#include <linux/kallsyms.h>
22#include <linux/notifier.h>
23#include <linux/kprobes.h>
24#include <linux/kdebug.h>
25#include <linux/kernel.h>
26#include <linux/module.h>
27#include <linux/percpu.h>
28#include <linux/sched.h>
29#include <linux/init.h>
30#include <linux/slab.h>
31#include <linux/list.h>
32#include <linux/cpu.h>
33#include <linux/smp.h>
34#include <linux/bug.h>
35
36#include <linux/hw_breakpoint.h>
37/*
38 * Constraints data
39 */
40struct bp_cpuinfo {
41 /* Number of pinned cpu breakpoints in a cpu */
42 unsigned int cpu_pinned;
43 /* tsk_pinned[n] is the number of tasks having n+1 breakpoints */
44 unsigned int *tsk_pinned;
45 /* Number of non-pinned cpu/task breakpoints in a cpu */
46 unsigned int flexible; /* XXX: placeholder, see fetch_this_slot() */
47};
48
49static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
50static int nr_slots[TYPE_MAX];
51
52static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type)
53{
54 return per_cpu_ptr(bp_cpuinfo + type, cpu);
55}
56
57/* Keep track of the breakpoints attached to tasks */
58static LIST_HEAD(bp_task_head);
59
60static int constraints_initialized;
61
62/* Gather the number of total pinned and un-pinned bp in a cpuset */
63struct bp_busy_slots {
64 unsigned int pinned;
65 unsigned int flexible;
66};
67
68/* Serialize accesses to the above constraints */
69static DEFINE_MUTEX(nr_bp_mutex);
70
71__weak int hw_breakpoint_weight(struct perf_event *bp)
72{
73 return 1;
74}
75
76static inline enum bp_type_idx find_slot_idx(u64 bp_type)
77{
78 if (bp_type & HW_BREAKPOINT_RW)
79 return TYPE_DATA;
80
81 return TYPE_INST;
82}
83
84/*
85 * Report the maximum number of pinned breakpoints a task
86 * have in this cpu
87 */
88static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
89{
90 unsigned int *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned;
91 int i;
92
93 for (i = nr_slots[type] - 1; i >= 0; i--) {
94 if (tsk_pinned[i] > 0)
95 return i + 1;
96 }
97
98 return 0;
99}
100
101/*
102 * Count the number of breakpoints of the same type and same task.
103 * The given event must be not on the list.
104 */
105static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
106{
107 struct task_struct *tsk = bp->hw.target;
108 struct perf_event *iter;
109 int count = 0;
110
111 list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
112 if (iter->hw.target == tsk &&
113 find_slot_idx(iter->attr.bp_type) == type &&
114 (iter->cpu < 0 || cpu == iter->cpu))
115 count += hw_breakpoint_weight(iter);
116 }
117
118 return count;
119}
120
121static const struct cpumask *cpumask_of_bp(struct perf_event *bp)
122{
123 if (bp->cpu >= 0)
124 return cpumask_of(bp->cpu);
125 return cpu_possible_mask;
126}
127
128/*
129 * Report the number of pinned/un-pinned breakpoints we have in
130 * a given cpu (cpu > -1) or in all of them (cpu = -1).
131 */
132static void
133fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp,
134 enum bp_type_idx type)
135{
136 const struct cpumask *cpumask = cpumask_of_bp(bp);
137 int cpu;
138
139 for_each_cpu(cpu, cpumask) {
140 struct bp_cpuinfo *info = get_bp_info(cpu, type);
141 int nr;
142
143 nr = info->cpu_pinned;
144 if (!bp->hw.target)
145 nr += max_task_bp_pinned(cpu, type);
146 else
147 nr += task_bp_pinned(cpu, bp, type);
148
149 if (nr > slots->pinned)
150 slots->pinned = nr;
151
152 nr = info->flexible;
153 if (nr > slots->flexible)
154 slots->flexible = nr;
155 }
156}
157
158/*
159 * For now, continue to consider flexible as pinned, until we can
160 * ensure no flexible event can ever be scheduled before a pinned event
161 * in a same cpu.
162 */
163static void
164fetch_this_slot(struct bp_busy_slots *slots, int weight)
165{
166 slots->pinned += weight;
167}
168
169/*
170 * Add a pinned breakpoint for the given task in our constraint table
171 */
172static void toggle_bp_task_slot(struct perf_event *bp, int cpu,
173 enum bp_type_idx type, int weight)
174{
175 unsigned int *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned;
176 int old_idx, new_idx;
177
178 old_idx = task_bp_pinned(cpu, bp, type) - 1;
179 new_idx = old_idx + weight;
180
181 if (old_idx >= 0)
182 tsk_pinned[old_idx]--;
183 if (new_idx >= 0)
184 tsk_pinned[new_idx]++;
185}
186
187/*
188 * Add/remove the given breakpoint in our constraint table
189 */
190static void
191toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
192 int weight)
193{
194 const struct cpumask *cpumask = cpumask_of_bp(bp);
195 int cpu;
196
197 if (!enable)
198 weight = -weight;
199
200 /* Pinned counter cpu profiling */
201 if (!bp->hw.target) {
202 get_bp_info(bp->cpu, type)->cpu_pinned += weight;
203 return;
204 }
205
206 /* Pinned counter task profiling */
207 for_each_cpu(cpu, cpumask)
208 toggle_bp_task_slot(bp, cpu, type, weight);
209
210 if (enable)
211 list_add_tail(&bp->hw.bp_list, &bp_task_head);
212 else
213 list_del(&bp->hw.bp_list);
214}
215
216__weak int arch_reserve_bp_slot(struct perf_event *bp)
217{
218 return 0;
219}
220
221__weak void arch_release_bp_slot(struct perf_event *bp)
222{
223}
224
225/*
226 * Function to perform processor-specific cleanup during unregistration
227 */
228__weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
229{
230 /*
231 * A weak stub function here for those archs that don't define
232 * it inside arch/.../kernel/hw_breakpoint.c
233 */
234}
235
236/*
237 * Constraints to check before allowing this new breakpoint counter:
238 *
239 * == Non-pinned counter == (Considered as pinned for now)
240 *
241 * - If attached to a single cpu, check:
242 *
243 * (per_cpu(info->flexible, cpu) || (per_cpu(info->cpu_pinned, cpu)
244 * + max(per_cpu(info->tsk_pinned, cpu)))) < HBP_NUM
245 *
246 * -> If there are already non-pinned counters in this cpu, it means
247 * there is already a free slot for them.
248 * Otherwise, we check that the maximum number of per task
249 * breakpoints (for this cpu) plus the number of per cpu breakpoint
250 * (for this cpu) doesn't cover every registers.
251 *
252 * - If attached to every cpus, check:
253 *
254 * (per_cpu(info->flexible, *) || (max(per_cpu(info->cpu_pinned, *))
255 * + max(per_cpu(info->tsk_pinned, *)))) < HBP_NUM
256 *
257 * -> This is roughly the same, except we check the number of per cpu
258 * bp for every cpu and we keep the max one. Same for the per tasks
259 * breakpoints.
260 *
261 *
262 * == Pinned counter ==
263 *
264 * - If attached to a single cpu, check:
265 *
266 * ((per_cpu(info->flexible, cpu) > 1) + per_cpu(info->cpu_pinned, cpu)
267 * + max(per_cpu(info->tsk_pinned, cpu))) < HBP_NUM
268 *
269 * -> Same checks as before. But now the info->flexible, if any, must keep
270 * one register at least (or they will never be fed).
271 *
272 * - If attached to every cpus, check:
273 *
274 * ((per_cpu(info->flexible, *) > 1) + max(per_cpu(info->cpu_pinned, *))
275 * + max(per_cpu(info->tsk_pinned, *))) < HBP_NUM
276 */
277static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
278{
279 struct bp_busy_slots slots = {0};
280 enum bp_type_idx type;
281 int weight;
282 int ret;
283
284 /* We couldn't initialize breakpoint constraints on boot */
285 if (!constraints_initialized)
286 return -ENOMEM;
287
288 /* Basic checks */
289 if (bp_type == HW_BREAKPOINT_EMPTY ||
290 bp_type == HW_BREAKPOINT_INVALID)
291 return -EINVAL;
292
293 type = find_slot_idx(bp_type);
294 weight = hw_breakpoint_weight(bp);
295
296 fetch_bp_busy_slots(&slots, bp, type);
297 /*
298 * Simulate the addition of this breakpoint to the constraints
299 * and see the result.
300 */
301 fetch_this_slot(&slots, weight);
302
303 /* Flexible counters need to keep at least one slot */
304 if (slots.pinned + (!!slots.flexible) > nr_slots[type])
305 return -ENOSPC;
306
307 ret = arch_reserve_bp_slot(bp);
308 if (ret)
309 return ret;
310
311 toggle_bp_slot(bp, true, type, weight);
312
313 return 0;
314}
315
316int reserve_bp_slot(struct perf_event *bp)
317{
318 int ret;
319
320 mutex_lock(&nr_bp_mutex);
321
322 ret = __reserve_bp_slot(bp, bp->attr.bp_type);
323
324 mutex_unlock(&nr_bp_mutex);
325
326 return ret;
327}
328
329static void __release_bp_slot(struct perf_event *bp, u64 bp_type)
330{
331 enum bp_type_idx type;
332 int weight;
333
334 arch_release_bp_slot(bp);
335
336 type = find_slot_idx(bp_type);
337 weight = hw_breakpoint_weight(bp);
338 toggle_bp_slot(bp, false, type, weight);
339}
340
341void release_bp_slot(struct perf_event *bp)
342{
343 mutex_lock(&nr_bp_mutex);
344
345 arch_unregister_hw_breakpoint(bp);
346 __release_bp_slot(bp, bp->attr.bp_type);
347
348 mutex_unlock(&nr_bp_mutex);
349}
350
351static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
352{
353 int err;
354
355 __release_bp_slot(bp, old_type);
356
357 err = __reserve_bp_slot(bp, new_type);
358 if (err) {
359 /*
360 * Reserve the old_type slot back in case
361 * there's no space for the new type.
362 *
363 * This must succeed, because we just released
364 * the old_type slot in the __release_bp_slot
365 * call above. If not, something is broken.
366 */
367 WARN_ON(__reserve_bp_slot(bp, old_type));
368 }
369
370 return err;
371}
372
373static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
374{
375 int ret;
376
377 mutex_lock(&nr_bp_mutex);
378 ret = __modify_bp_slot(bp, old_type, new_type);
379 mutex_unlock(&nr_bp_mutex);
380 return ret;
381}
382
383/*
384 * Allow the kernel debugger to reserve breakpoint slots without
385 * taking a lock using the dbg_* variant of for the reserve and
386 * release breakpoint slots.
387 */
388int dbg_reserve_bp_slot(struct perf_event *bp)
389{
390 if (mutex_is_locked(&nr_bp_mutex))
391 return -1;
392
393 return __reserve_bp_slot(bp, bp->attr.bp_type);
394}
395
396int dbg_release_bp_slot(struct perf_event *bp)
397{
398 if (mutex_is_locked(&nr_bp_mutex))
399 return -1;
400
401 __release_bp_slot(bp, bp->attr.bp_type);
402
403 return 0;
404}
405
406static int hw_breakpoint_parse(struct perf_event *bp,
407 const struct perf_event_attr *attr,
408 struct arch_hw_breakpoint *hw)
409{
410 int err;
411
412 err = hw_breakpoint_arch_parse(bp, attr, hw);
413 if (err)
414 return err;
415
416 if (arch_check_bp_in_kernelspace(hw)) {
417 if (attr->exclude_kernel)
418 return -EINVAL;
419 /*
420 * Don't let unprivileged users set a breakpoint in the trap
421 * path to avoid trap recursion attacks.
422 */
423 if (!capable(CAP_SYS_ADMIN))
424 return -EPERM;
425 }
426
427 return 0;
428}
429
430int register_perf_hw_breakpoint(struct perf_event *bp)
431{
432 struct arch_hw_breakpoint hw = { };
433 int err;
434
435 err = reserve_bp_slot(bp);
436 if (err)
437 return err;
438
439 err = hw_breakpoint_parse(bp, &bp->attr, &hw);
440 if (err) {
441 release_bp_slot(bp);
442 return err;
443 }
444
445 bp->hw.info = hw;
446
447 return 0;
448}
449
450/**
451 * register_user_hw_breakpoint - register a hardware breakpoint for user space
452 * @attr: breakpoint attributes
453 * @triggered: callback to trigger when we hit the breakpoint
454 * @tsk: pointer to 'task_struct' of the process to which the address belongs
455 */
456struct perf_event *
457register_user_hw_breakpoint(struct perf_event_attr *attr,
458 perf_overflow_handler_t triggered,
459 void *context,
460 struct task_struct *tsk)
461{
462 return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
463 context);
464}
465EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
466
467static void hw_breakpoint_copy_attr(struct perf_event_attr *to,
468 struct perf_event_attr *from)
469{
470 to->bp_addr = from->bp_addr;
471 to->bp_type = from->bp_type;
472 to->bp_len = from->bp_len;
473 to->disabled = from->disabled;
474}
475
476int
477modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
478 bool check)
479{
480 struct arch_hw_breakpoint hw = { };
481 int err;
482
483 err = hw_breakpoint_parse(bp, attr, &hw);
484 if (err)
485 return err;
486
487 if (check) {
488 struct perf_event_attr old_attr;
489
490 old_attr = bp->attr;
491 hw_breakpoint_copy_attr(&old_attr, attr);
492 if (memcmp(&old_attr, attr, sizeof(*attr)))
493 return -EINVAL;
494 }
495
496 if (bp->attr.bp_type != attr->bp_type) {
497 err = modify_bp_slot(bp, bp->attr.bp_type, attr->bp_type);
498 if (err)
499 return err;
500 }
501
502 hw_breakpoint_copy_attr(&bp->attr, attr);
503 bp->hw.info = hw;
504
505 return 0;
506}
507
508/**
509 * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
510 * @bp: the breakpoint structure to modify
511 * @attr: new breakpoint attributes
512 */
513int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
514{
515 int err;
516
517 /*
518 * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
519 * will not be possible to raise IPIs that invoke __perf_event_disable.
520 * So call the function directly after making sure we are targeting the
521 * current task.
522 */
523 if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
524 perf_event_disable_local(bp);
525 else
526 perf_event_disable(bp);
527
528 err = modify_user_hw_breakpoint_check(bp, attr, false);
529
530 if (!bp->attr.disabled)
531 perf_event_enable(bp);
532
533 return err;
534}
535EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
536
537/**
538 * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
539 * @bp: the breakpoint structure to unregister
540 */
541void unregister_hw_breakpoint(struct perf_event *bp)
542{
543 if (!bp)
544 return;
545 perf_event_release_kernel(bp);
546}
547EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
548
549/**
550 * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
551 * @attr: breakpoint attributes
552 * @triggered: callback to trigger when we hit the breakpoint
553 *
554 * @return a set of per_cpu pointers to perf events
555 */
556struct perf_event * __percpu *
557register_wide_hw_breakpoint(struct perf_event_attr *attr,
558 perf_overflow_handler_t triggered,
559 void *context)
560{
561 struct perf_event * __percpu *cpu_events, *bp;
562 long err = 0;
563 int cpu;
564
565 cpu_events = alloc_percpu(typeof(*cpu_events));
566 if (!cpu_events)
567 return (void __percpu __force *)ERR_PTR(-ENOMEM);
568
569 get_online_cpus();
570 for_each_online_cpu(cpu) {
571 bp = perf_event_create_kernel_counter(attr, cpu, NULL,
572 triggered, context);
573 if (IS_ERR(bp)) {
574 err = PTR_ERR(bp);
575 break;
576 }
577
578 per_cpu(*cpu_events, cpu) = bp;
579 }
580 put_online_cpus();
581
582 if (likely(!err))
583 return cpu_events;
584
585 unregister_wide_hw_breakpoint(cpu_events);
586 return (void __percpu __force *)ERR_PTR(err);
587}
588EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
589
590/**
591 * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
592 * @cpu_events: the per cpu set of events to unregister
593 */
594void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
595{
596 int cpu;
597
598 for_each_possible_cpu(cpu)
599 unregister_hw_breakpoint(per_cpu(*cpu_events, cpu));
600
601 free_percpu(cpu_events);
602}
603EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
604
605static struct notifier_block hw_breakpoint_exceptions_nb = {
606 .notifier_call = hw_breakpoint_exceptions_notify,
607 /* we need to be notified first */
608 .priority = 0x7fffffff
609};
610
611static void bp_perf_event_destroy(struct perf_event *event)
612{
613 release_bp_slot(event);
614}
615
616static int hw_breakpoint_event_init(struct perf_event *bp)
617{
618 int err;
619
620 if (bp->attr.type != PERF_TYPE_BREAKPOINT)
621 return -ENOENT;
622
623 /*
624 * no branch sampling for breakpoint events
625 */
626 if (has_branch_stack(bp))
627 return -EOPNOTSUPP;
628
629 err = register_perf_hw_breakpoint(bp);
630 if (err)
631 return err;
632
633 bp->destroy = bp_perf_event_destroy;
634
635 return 0;
636}
637
638static int hw_breakpoint_add(struct perf_event *bp, int flags)
639{
640 if (!(flags & PERF_EF_START))
641 bp->hw.state = PERF_HES_STOPPED;
642
643 if (is_sampling_event(bp)) {
644 bp->hw.last_period = bp->hw.sample_period;
645 perf_swevent_set_period(bp);
646 }
647
648 return arch_install_hw_breakpoint(bp);
649}
650
651static void hw_breakpoint_del(struct perf_event *bp, int flags)
652{
653 arch_uninstall_hw_breakpoint(bp);
654}
655
656static void hw_breakpoint_start(struct perf_event *bp, int flags)
657{
658 bp->hw.state = 0;
659}
660
661static void hw_breakpoint_stop(struct perf_event *bp, int flags)
662{
663 bp->hw.state = PERF_HES_STOPPED;
664}
665
666static struct pmu perf_breakpoint = {
667 .task_ctx_nr = perf_sw_context, /* could eventually get its own */
668
669 .event_init = hw_breakpoint_event_init,
670 .add = hw_breakpoint_add,
671 .del = hw_breakpoint_del,
672 .start = hw_breakpoint_start,
673 .stop = hw_breakpoint_stop,
674 .read = hw_breakpoint_pmu_read,
675};
676
677int __init init_hw_breakpoint(void)
678{
679 int cpu, err_cpu;
680 int i;
681
682 for (i = 0; i < TYPE_MAX; i++)
683 nr_slots[i] = hw_breakpoint_slots(i);
684
685 for_each_possible_cpu(cpu) {
686 for (i = 0; i < TYPE_MAX; i++) {
687 struct bp_cpuinfo *info = get_bp_info(cpu, i);
688
689 info->tsk_pinned = kcalloc(nr_slots[i], sizeof(int),
690 GFP_KERNEL);
691 if (!info->tsk_pinned)
692 goto err_alloc;
693 }
694 }
695
696 constraints_initialized = 1;
697
698 perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
699
700 return register_die_notifier(&hw_breakpoint_exceptions_nb);
701
702 err_alloc:
703 for_each_possible_cpu(err_cpu) {
704 for (i = 0; i < TYPE_MAX; i++)
705 kfree(get_bp_info(err_cpu, i)->tsk_pinned);
706 if (err_cpu == cpu)
707 break;
708 }
709
710 return -ENOMEM;
711}
712
713