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(sem: &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(sem: &bp_cpuinfo_sem);
143 mutex_unlock(lock: 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(sem: &bp_cpuinfo_sem) ||
154 (tsk_mtx ? mutex_is_locked(lock: 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(v: &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(v: &hist1->count[i]);
270 const int count2 = atomic_read(v: &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(hist1: tsk_pinned, hist2: &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(hlt: &task_bps_ht, key: &bp->hw.target, params: 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(bp_type: 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(bp: 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(cpu: -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(hist: &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(cpu: bp->cpu, type);
422
423 lockdep_assert_held_write(&bp_cpuinfo_sem);
424 bp_slots_histogram_add(hist: &cpu_pinned[type], old: info->cpu_pinned, val: 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(hlt: &task_bps_ht, list: &bp->hw.bp_list, params: 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(cpu: -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(hist: &tsk_pinned_all[type], old: next_tsk_pinned, val: 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(hist: &get_bp_info(cpu, type)->tsk_pinned,
483 old: 0, val: next_tsk_pinned);
484 }
485 /* Add this first CPU-pinned task breakpoint. */
486 bp_slots_histogram_add(hist: &get_bp_info(cpu: bp->cpu, type)->tsk_pinned,
487 old: next_tsk_pinned, val: weight);
488 /* Rebalance global task pinned histogram. */
489 bp_slots_histogram_add(hist: &tsk_pinned_all[type], old: next_tsk_pinned,
490 val: -next_tsk_pinned);
491 } else { /* Case 2.b: slow path */
492 /* Remove this last CPU-pinned task breakpoint. */
493 bp_slots_histogram_add(hist: &get_bp_info(cpu: bp->cpu, type)->tsk_pinned,
494 old: next_tsk_pinned + hw_breakpoint_weight(bp), val: weight);
495 /* Remove all from per-CPU histograms. */
496 for_each_possible_cpu(cpu) {
497 bp_slots_histogram_add(hist: &get_bp_info(cpu, type)->tsk_pinned,
498 old: next_tsk_pinned, val: -next_tsk_pinned);
499 }
500 /* Rebalance global task pinned histogram. */
501 bp_slots_histogram_add(hist: &tsk_pinned_all[type], old: 0, val: 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(hist: &get_bp_info(cpu, type)->tsk_pinned,
511 old: next_tsk_pinned, val: 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(hlt: &task_bps_ht, list: &bp->hw.bp_list, params: task_bps_ht_params);
522
523 return 0;
524}
525
526/*
527 * Constraints to check before allowing this new breakpoint counter.
528 *
529 * Note: Flexible breakpoints are currently unimplemented, but outlined in the
530 * below algorithm for completeness. The implementation treats flexible as
531 * pinned due to no guarantee that we currently always schedule flexible events
532 * before a pinned event in a same CPU.
533 *
534 * == Non-pinned counter == (Considered as pinned for now)
535 *
536 * - If attached to a single cpu, check:
537 *
538 * (per_cpu(info->flexible, cpu) || (per_cpu(info->cpu_pinned, cpu)
539 * + max(per_cpu(info->tsk_pinned, cpu)))) < HBP_NUM
540 *
541 * -> If there are already non-pinned counters in this cpu, it means
542 * there is already a free slot for them.
543 * Otherwise, we check that the maximum number of per task
544 * breakpoints (for this cpu) plus the number of per cpu breakpoint
545 * (for this cpu) doesn't cover every registers.
546 *
547 * - If attached to every cpus, check:
548 *
549 * (per_cpu(info->flexible, *) || (max(per_cpu(info->cpu_pinned, *))
550 * + max(per_cpu(info->tsk_pinned, *)))) < HBP_NUM
551 *
552 * -> This is roughly the same, except we check the number of per cpu
553 * bp for every cpu and we keep the max one. Same for the per tasks
554 * breakpoints.
555 *
556 *
557 * == Pinned counter ==
558 *
559 * - If attached to a single cpu, check:
560 *
561 * ((per_cpu(info->flexible, cpu) > 1) + per_cpu(info->cpu_pinned, cpu)
562 * + max(per_cpu(info->tsk_pinned, cpu))) < HBP_NUM
563 *
564 * -> Same checks as before. But now the info->flexible, if any, must keep
565 * one register at least (or they will never be fed).
566 *
567 * - If attached to every cpus, check:
568 *
569 * ((per_cpu(info->flexible, *) > 1) + max(per_cpu(info->cpu_pinned, *))
570 * + max(per_cpu(info->tsk_pinned, *))) < HBP_NUM
571 */
572static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
573{
574 enum bp_type_idx type;
575 int max_pinned_slots;
576 int weight;
577
578 /* We couldn't initialize breakpoint constraints on boot */
579 if (!constraints_initialized)
580 return -ENOMEM;
581
582 /* Basic checks */
583 if (bp_type == HW_BREAKPOINT_EMPTY ||
584 bp_type == HW_BREAKPOINT_INVALID)
585 return -EINVAL;
586
587 type = find_slot_idx(bp_type);
588 weight = hw_breakpoint_weight(bp);
589
590 /* Check if this new breakpoint can be satisfied across all CPUs. */
591 max_pinned_slots = max_bp_pinned_slots(bp, type) + weight;
592 if (max_pinned_slots > hw_breakpoint_slots_cached(type))
593 return -ENOSPC;
594
595 return toggle_bp_slot(bp, enable: true, type, weight);
596}
597
598int reserve_bp_slot(struct perf_event *bp)
599{
600 struct mutex *mtx = bp_constraints_lock(bp);
601 int ret = __reserve_bp_slot(bp, bp_type: bp->attr.bp_type);
602
603 bp_constraints_unlock(tsk_mtx: mtx);
604 return ret;
605}
606
607static void __release_bp_slot(struct perf_event *bp, u64 bp_type)
608{
609 enum bp_type_idx type;
610 int weight;
611
612 type = find_slot_idx(bp_type);
613 weight = hw_breakpoint_weight(bp);
614 WARN_ON(toggle_bp_slot(bp, false, type, weight));
615}
616
617void release_bp_slot(struct perf_event *bp)
618{
619 struct mutex *mtx = bp_constraints_lock(bp);
620
621 __release_bp_slot(bp, bp_type: bp->attr.bp_type);
622 bp_constraints_unlock(tsk_mtx: mtx);
623}
624
625static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
626{
627 int err;
628
629 __release_bp_slot(bp, bp_type: old_type);
630
631 err = __reserve_bp_slot(bp, bp_type: new_type);
632 if (err) {
633 /*
634 * Reserve the old_type slot back in case
635 * there's no space for the new type.
636 *
637 * This must succeed, because we just released
638 * the old_type slot in the __release_bp_slot
639 * call above. If not, something is broken.
640 */
641 WARN_ON(__reserve_bp_slot(bp, old_type));
642 }
643
644 return err;
645}
646
647static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
648{
649 struct mutex *mtx = bp_constraints_lock(bp);
650 int ret = __modify_bp_slot(bp, old_type, new_type);
651
652 bp_constraints_unlock(tsk_mtx: mtx);
653 return ret;
654}
655
656/*
657 * Allow the kernel debugger to reserve breakpoint slots without
658 * taking a lock using the dbg_* variant of for the reserve and
659 * release breakpoint slots.
660 */
661int dbg_reserve_bp_slot(struct perf_event *bp)
662{
663 int ret;
664
665 if (bp_constraints_is_locked(bp))
666 return -1;
667
668 /* Locks aren't held; disable lockdep assert checking. */
669 lockdep_off();
670 ret = __reserve_bp_slot(bp, bp_type: bp->attr.bp_type);
671 lockdep_on();
672
673 return ret;
674}
675
676int dbg_release_bp_slot(struct perf_event *bp)
677{
678 if (bp_constraints_is_locked(bp))
679 return -1;
680
681 /* Locks aren't held; disable lockdep assert checking. */
682 lockdep_off();
683 __release_bp_slot(bp, bp_type: bp->attr.bp_type);
684 lockdep_on();
685
686 return 0;
687}
688
689static int hw_breakpoint_parse(struct perf_event *bp,
690 const struct perf_event_attr *attr,
691 struct arch_hw_breakpoint *hw)
692{
693 int err;
694
695 err = hw_breakpoint_arch_parse(bp, attr, hw);
696 if (err)
697 return err;
698
699 if (arch_check_bp_in_kernelspace(hw)) {
700 if (attr->exclude_kernel)
701 return -EINVAL;
702 /*
703 * Don't let unprivileged users set a breakpoint in the trap
704 * path to avoid trap recursion attacks.
705 */
706 if (!capable(CAP_SYS_ADMIN))
707 return -EPERM;
708 }
709
710 return 0;
711}
712
713int register_perf_hw_breakpoint(struct perf_event *bp)
714{
715 struct arch_hw_breakpoint hw = { };
716 int err;
717
718 err = reserve_bp_slot(bp);
719 if (err)
720 return err;
721
722 err = hw_breakpoint_parse(bp, attr: &bp->attr, hw: &hw);
723 if (err) {
724 release_bp_slot(bp);
725 return err;
726 }
727
728 bp->hw.info = hw;
729
730 return 0;
731}
732
733/**
734 * register_user_hw_breakpoint - register a hardware breakpoint for user space
735 * @attr: breakpoint attributes
736 * @triggered: callback to trigger when we hit the breakpoint
737 * @context: context data could be used in the triggered callback
738 * @tsk: pointer to 'task_struct' of the process to which the address belongs
739 */
740struct perf_event *
741register_user_hw_breakpoint(struct perf_event_attr *attr,
742 perf_overflow_handler_t triggered,
743 void *context,
744 struct task_struct *tsk)
745{
746 return perf_event_create_kernel_counter(attr, cpu: -1, task: tsk, callback: triggered,
747 context);
748}
749EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
750
751static void hw_breakpoint_copy_attr(struct perf_event_attr *to,
752 struct perf_event_attr *from)
753{
754 to->bp_addr = from->bp_addr;
755 to->bp_type = from->bp_type;
756 to->bp_len = from->bp_len;
757 to->disabled = from->disabled;
758}
759
760int
761modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
762 bool check)
763{
764 struct arch_hw_breakpoint hw = { };
765 int err;
766
767 err = hw_breakpoint_parse(bp, attr, hw: &hw);
768 if (err)
769 return err;
770
771 if (check) {
772 struct perf_event_attr old_attr;
773
774 old_attr = bp->attr;
775 hw_breakpoint_copy_attr(to: &old_attr, from: attr);
776 if (memcmp(&old_attr, attr, sizeof(*attr)))
777 return -EINVAL;
778 }
779
780 if (bp->attr.bp_type != attr->bp_type) {
781 err = modify_bp_slot(bp, old_type: bp->attr.bp_type, new_type: attr->bp_type);
782 if (err)
783 return err;
784 }
785
786 hw_breakpoint_copy_attr(to: &bp->attr, from: attr);
787 bp->hw.info = hw;
788
789 return 0;
790}
791
792/**
793 * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
794 * @bp: the breakpoint structure to modify
795 * @attr: new breakpoint attributes
796 */
797int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
798{
799 int err;
800
801 /*
802 * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
803 * will not be possible to raise IPIs that invoke __perf_event_disable.
804 * So call the function directly after making sure we are targeting the
805 * current task.
806 */
807 if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
808 perf_event_disable_local(event: bp);
809 else
810 perf_event_disable(event: bp);
811
812 err = modify_user_hw_breakpoint_check(bp, attr, check: false);
813
814 if (!bp->attr.disabled)
815 perf_event_enable(event: bp);
816
817 return err;
818}
819EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
820
821/**
822 * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
823 * @bp: the breakpoint structure to unregister
824 */
825void unregister_hw_breakpoint(struct perf_event *bp)
826{
827 if (!bp)
828 return;
829 perf_event_release_kernel(event: bp);
830}
831EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
832
833/**
834 * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
835 * @attr: breakpoint attributes
836 * @triggered: callback to trigger when we hit the breakpoint
837 * @context: context data could be used in the triggered callback
838 *
839 * @return a set of per_cpu pointers to perf events
840 */
841struct perf_event * __percpu *
842register_wide_hw_breakpoint(struct perf_event_attr *attr,
843 perf_overflow_handler_t triggered,
844 void *context)
845{
846 struct perf_event * __percpu *cpu_events, *bp;
847 long err = 0;
848 int cpu;
849
850 cpu_events = alloc_percpu(typeof(*cpu_events));
851 if (!cpu_events)
852 return ERR_PTR_PCPU(-ENOMEM);
853
854 cpus_read_lock();
855 for_each_online_cpu(cpu) {
856 bp = perf_event_create_kernel_counter(attr, cpu, NULL,
857 callback: triggered, context);
858 if (IS_ERR(ptr: bp)) {
859 err = PTR_ERR(ptr: bp);
860 break;
861 }
862
863 per_cpu(*cpu_events, cpu) = bp;
864 }
865 cpus_read_unlock();
866
867 if (likely(!err))
868 return cpu_events;
869
870 unregister_wide_hw_breakpoint(cpu_events);
871 return ERR_PTR_PCPU(err);
872}
873EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
874
875/**
876 * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
877 * @cpu_events: the per cpu set of events to unregister
878 */
879void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
880{
881 int cpu;
882
883 for_each_possible_cpu(cpu)
884 unregister_hw_breakpoint(per_cpu(*cpu_events, cpu));
885
886 free_percpu(pdata: cpu_events);
887}
888EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
889
890/**
891 * hw_breakpoint_is_used - check if breakpoints are currently used
892 *
893 * Returns: true if breakpoints are used, false otherwise.
894 */
895bool hw_breakpoint_is_used(void)
896{
897 int cpu;
898
899 if (!constraints_initialized)
900 return false;
901
902 for_each_possible_cpu(cpu) {
903 for (int type = 0; type < TYPE_MAX; ++type) {
904 struct bp_cpuinfo *info = get_bp_info(cpu, type);
905
906 if (info->cpu_pinned)
907 return true;
908
909 for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) {
910 if (atomic_read(v: &info->tsk_pinned.count[slot]))
911 return true;
912 }
913 }
914 }
915
916 for (int type = 0; type < TYPE_MAX; ++type) {
917 for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) {
918 /*
919 * Warn, because if there are CPU pinned counters,
920 * should never get here; bp_cpuinfo::cpu_pinned should
921 * be consistent with the global cpu_pinned histogram.
922 */
923 if (WARN_ON(atomic_read(&cpu_pinned[type].count[slot])))
924 return true;
925
926 if (atomic_read(v: &tsk_pinned_all[type].count[slot]))
927 return true;
928 }
929 }
930
931 return false;
932}
933
934static struct notifier_block hw_breakpoint_exceptions_nb = {
935 .notifier_call = hw_breakpoint_exceptions_notify,
936 /* we need to be notified first */
937 .priority = 0x7fffffff
938};
939
940static void bp_perf_event_destroy(struct perf_event *event)
941{
942 release_bp_slot(bp: event);
943}
944
945static int hw_breakpoint_event_init(struct perf_event *bp)
946{
947 int err;
948
949 if (bp->attr.type != PERF_TYPE_BREAKPOINT)
950 return -ENOENT;
951
952 /*
953 * Check if breakpoint type is supported before proceeding.
954 * Also, no branch sampling for breakpoint events.
955 */
956 if (!hw_breakpoint_slots_cached(type: find_slot_idx(bp_type: bp->attr.bp_type)) || has_branch_stack(event: bp))
957 return -EOPNOTSUPP;
958
959 err = register_perf_hw_breakpoint(bp);
960 if (err)
961 return err;
962
963 bp->destroy = bp_perf_event_destroy;
964
965 return 0;
966}
967
968static int hw_breakpoint_add(struct perf_event *bp, int flags)
969{
970 if (!(flags & PERF_EF_START))
971 bp->hw.state = PERF_HES_STOPPED;
972
973 if (is_sampling_event(event: bp)) {
974 bp->hw.last_period = bp->hw.sample_period;
975 perf_swevent_set_period(event: bp);
976 }
977
978 return arch_install_hw_breakpoint(bp);
979}
980
981static void hw_breakpoint_del(struct perf_event *bp, int flags)
982{
983 arch_uninstall_hw_breakpoint(bp);
984}
985
986static void hw_breakpoint_start(struct perf_event *bp, int flags)
987{
988 bp->hw.state = 0;
989}
990
991static void hw_breakpoint_stop(struct perf_event *bp, int flags)
992{
993 bp->hw.state = PERF_HES_STOPPED;
994}
995
996static struct pmu perf_breakpoint = {
997 .task_ctx_nr = perf_sw_context, /* could eventually get its own */
998
999 .event_init = hw_breakpoint_event_init,
1000 .add = hw_breakpoint_add,
1001 .del = hw_breakpoint_del,
1002 .start = hw_breakpoint_start,
1003 .stop = hw_breakpoint_stop,
1004 .read = hw_breakpoint_pmu_read,
1005};
1006
1007int __init init_hw_breakpoint(void)
1008{
1009 int ret;
1010
1011 ret = rhltable_init(&task_bps_ht, &task_bps_ht_params);
1012 if (ret)
1013 return ret;
1014
1015 ret = init_breakpoint_slots();
1016 if (ret)
1017 return ret;
1018
1019 constraints_initialized = true;
1020
1021 perf_pmu_register(pmu: &perf_breakpoint, name: "breakpoint", type: PERF_TYPE_BREAKPOINT);
1022
1023 return register_die_notifier(nb: &hw_breakpoint_exceptions_nb);
1024}
1025