1 /*
2 * Performance events ring-buffer code:
3 *
4 * Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
5 * Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
6 * Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
7 * Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
8 *
9 * For licensing details see kernel-base/COPYING
10 */
11
12 #include <linux/perf_event.h>
13 #include <linux/vmalloc.h>
14 #include <linux/slab.h>
15 #include <linux/circ_buf.h>
16 #include <linux/poll.h>
17
18 #include "internal.h"
19
20 static void perf_output_wakeup(struct perf_output_handle *handle)
21 {
22 atomic_set(&handle->rb->poll, POLLIN);
23
24 handle->event->pending_wakeup = 1;
25 irq_work_queue(&handle->event->pending);
26 }
27
28 /*
29 * We need to ensure a later event_id doesn't publish a head when a former
30 * event isn't done writing. However since we need to deal with NMIs we
31 * cannot fully serialize things.
32 *
33 * We only publish the head (and generate a wakeup) when the outer-most
34 * event completes.
35 */
36 static void perf_output_get_handle(struct perf_output_handle *handle)
37 {
38 struct ring_buffer *rb = handle->rb;
39
40 preempt_disable();
41 local_inc(&rb->nest);
42 handle->wakeup = local_read(&rb->wakeup);
43 }
44
45 static void perf_output_put_handle(struct perf_output_handle *handle)
46 {
47 struct ring_buffer *rb = handle->rb;
48 unsigned long head;
49
50 again:
51 head = local_read(&rb->head);
52
53 /*
54 * IRQ/NMI can happen here, which means we can miss a head update.
55 */
56
57 if (!local_dec_and_test(&rb->nest))
58 goto out;
59
60 /*
61 * Since the mmap() consumer (userspace) can run on a different CPU:
62 *
63 * kernel user
64 *
65 * if (LOAD ->data_tail) { LOAD ->data_head
66 * (A) smp_rmb() (C)
67 * STORE $data LOAD $data
68 * smp_wmb() (B) smp_mb() (D)
69 * STORE ->data_head STORE ->data_tail
70 * }
71 *
72 * Where A pairs with D, and B pairs with C.
73 *
74 * In our case (A) is a control dependency that separates the load of
75 * the ->data_tail and the stores of $data. In case ->data_tail
76 * indicates there is no room in the buffer to store $data we do not.
77 *
78 * D needs to be a full barrier since it separates the data READ
79 * from the tail WRITE.
80 *
81 * For B a WMB is sufficient since it separates two WRITEs, and for C
82 * an RMB is sufficient since it separates two READs.
83 *
84 * See perf_output_begin().
85 */
86 smp_wmb(); /* B, matches C */
87 rb->user_page->data_head = head;
88
89 /*
90 * Now check if we missed an update -- rely on previous implied
91 * compiler barriers to force a re-read.
92 */
93 if (unlikely(head != local_read(&rb->head))) {
94 local_inc(&rb->nest);
95 goto again;
96 }
97
98 if (handle->wakeup != local_read(&rb->wakeup))
99 perf_output_wakeup(handle);
100
101 out:
102 preempt_enable();
103 }
104
105 int perf_output_begin(struct perf_output_handle *handle,
106 struct perf_event *event, unsigned int size)
107 {
108 struct ring_buffer *rb;
109 unsigned long tail, offset, head;
110 int have_lost, page_shift;
111 struct {
112 struct perf_event_header header;
113 u64 id;
114 u64 lost;
115 } lost_event;
116
117 rcu_read_lock();
118 /*
119 * For inherited events we send all the output towards the parent.
120 */
121 if (event->parent)
122 event = event->parent;
123
124 rb = rcu_dereference(event->rb);
125 if (unlikely(!rb))
126 goto out;
127
128 if (unlikely(!rb->nr_pages))
129 goto out;
130
131 handle->rb = rb;
132 handle->event = event;
133
134 have_lost = local_read(&rb->lost);
135 if (unlikely(have_lost)) {
136 size += sizeof(lost_event);
137 if (event->attr.sample_id_all)
138 size += event->id_header_size;
139 }
140
141 perf_output_get_handle(handle);
142
143 do {
144 tail = READ_ONCE(rb->user_page->data_tail);
145 offset = head = local_read(&rb->head);
146 if (!rb->overwrite &&
147 unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size))
148 goto fail;
149
150 /*
151 * The above forms a control dependency barrier separating the
152 * @tail load above from the data stores below. Since the @tail
153 * load is required to compute the branch to fail below.
154 *
155 * A, matches D; the full memory barrier userspace SHOULD issue
156 * after reading the data and before storing the new tail
157 * position.
158 *
159 * See perf_output_put_handle().
160 */
161
162 head += size;
163 } while (local_cmpxchg(&rb->head, offset, head) != offset);
164
165 /*
166 * We rely on the implied barrier() by local_cmpxchg() to ensure
167 * none of the data stores below can be lifted up by the compiler.
168 */
169
170 if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
171 local_add(rb->watermark, &rb->wakeup);
172
173 page_shift = PAGE_SHIFT + page_order(rb);
174
175 handle->page = (offset >> page_shift) & (rb->nr_pages - 1);
176 offset &= (1UL << page_shift) - 1;
177 handle->addr = rb->data_pages[handle->page] + offset;
178 handle->size = (1UL << page_shift) - offset;
179
180 if (unlikely(have_lost)) {
181 struct perf_sample_data sample_data;
182
183 lost_event.header.size = sizeof(lost_event);
184 lost_event.header.type = PERF_RECORD_LOST;
185 lost_event.header.misc = 0;
186 lost_event.id = event->id;
187 lost_event.lost = local_xchg(&rb->lost, 0);
188
189 perf_event_header__init_id(&lost_event.header,
190 &sample_data, event);
191 perf_output_put(handle, lost_event);
192 perf_event__output_id_sample(event, handle, &sample_data);
193 }
194
195 return 0;
196
197 fail:
198 local_inc(&rb->lost);
199 perf_output_put_handle(handle);
200 out:
201 rcu_read_unlock();
202
203 return -ENOSPC;
204 }
205
206 unsigned int perf_output_copy(struct perf_output_handle *handle,
207 const void *buf, unsigned int len)
208 {
209 return __output_copy(handle, buf, len);
210 }
211
212 unsigned int perf_output_skip(struct perf_output_handle *handle,
213 unsigned int len)
214 {
215 return __output_skip(handle, NULL, len);
216 }
217
218 void perf_output_end(struct perf_output_handle *handle)
219 {
220 perf_output_put_handle(handle);
221 rcu_read_unlock();
222 }
223
224 static void rb_irq_work(struct irq_work *work);
225
226 static void
227 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
228 {
229 long max_size = perf_data_size(rb);
230
231 if (watermark)
232 rb->watermark = min(max_size, watermark);
233
234 if (!rb->watermark)
235 rb->watermark = max_size / 2;
236
237 if (flags & RING_BUFFER_WRITABLE)
238 rb->overwrite = 0;
239 else
240 rb->overwrite = 1;
241
242 atomic_set(&rb->refcount, 1);
243
244 INIT_LIST_HEAD(&rb->event_list);
245 spin_lock_init(&rb->event_lock);
246 init_irq_work(&rb->irq_work, rb_irq_work);
247 }
248
249 static void ring_buffer_put_async(struct ring_buffer *rb)
250 {
251 if (!atomic_dec_and_test(&rb->refcount))
252 return;
253
254 rb->rcu_head.next = (void *)rb;
255 irq_work_queue(&rb->irq_work);
256 }
257
258 /*
259 * This is called before hardware starts writing to the AUX area to
260 * obtain an output handle and make sure there's room in the buffer.
261 * When the capture completes, call perf_aux_output_end() to commit
262 * the recorded data to the buffer.
263 *
264 * The ordering is similar to that of perf_output_{begin,end}, with
265 * the exception of (B), which should be taken care of by the pmu
266 * driver, since ordering rules will differ depending on hardware.
267 */
268 void *perf_aux_output_begin(struct perf_output_handle *handle,
269 struct perf_event *event)
270 {
271 struct perf_event *output_event = event;
272 unsigned long aux_head, aux_tail;
273 struct ring_buffer *rb;
274
275 if (output_event->parent)
276 output_event = output_event->parent;
277
278 /*
279 * Since this will typically be open across pmu::add/pmu::del, we
280 * grab ring_buffer's refcount instead of holding rcu read lock
281 * to make sure it doesn't disappear under us.
282 */
283 rb = ring_buffer_get(output_event);
284 if (!rb)
285 return NULL;
286
287 if (!rb_has_aux(rb) || !atomic_inc_not_zero(&rb->aux_refcount))
288 goto err;
289
290 /*
291 * Nesting is not supported for AUX area, make sure nested
292 * writers are caught early
293 */
294 if (WARN_ON_ONCE(local_xchg(&rb->aux_nest, 1)))
295 goto err_put;
296
297 aux_head = local_read(&rb->aux_head);
298
299 handle->rb = rb;
300 handle->event = event;
301 handle->head = aux_head;
302 handle->size = 0;
303
304 /*
305 * In overwrite mode, AUX data stores do not depend on aux_tail,
306 * therefore (A) control dependency barrier does not exist. The
307 * (B) <-> (C) ordering is still observed by the pmu driver.
308 */
309 if (!rb->aux_overwrite) {
310 aux_tail = ACCESS_ONCE(rb->user_page->aux_tail);
311 handle->wakeup = local_read(&rb->aux_wakeup) + rb->aux_watermark;
312 if (aux_head - aux_tail < perf_aux_size(rb))
313 handle->size = CIRC_SPACE(aux_head, aux_tail, perf_aux_size(rb));
314
315 /*
316 * handle->size computation depends on aux_tail load; this forms a
317 * control dependency barrier separating aux_tail load from aux data
318 * store that will be enabled on successful return
319 */
320 if (!handle->size) { /* A, matches D */
321 event->pending_disable = 1;
322 perf_output_wakeup(handle);
323 local_set(&rb->aux_nest, 0);
324 goto err_put;
325 }
326 }
327
328 return handle->rb->aux_priv;
329
330 err_put:
331 rb_free_aux(rb);
332
333 err:
334 ring_buffer_put_async(rb);
335 handle->event = NULL;
336
337 return NULL;
338 }
339
340 /*
341 * Commit the data written by hardware into the ring buffer by adjusting
342 * aux_head and posting a PERF_RECORD_AUX into the perf buffer. It is the
343 * pmu driver's responsibility to observe ordering rules of the hardware,
344 * so that all the data is externally visible before this is called.
345 */
346 void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
347 bool truncated)
348 {
349 struct ring_buffer *rb = handle->rb;
350 bool wakeup = truncated;
351 unsigned long aux_head;
352 u64 flags = 0;
353
354 if (truncated)
355 flags |= PERF_AUX_FLAG_TRUNCATED;
356
357 /* in overwrite mode, driver provides aux_head via handle */
358 if (rb->aux_overwrite) {
359 flags |= PERF_AUX_FLAG_OVERWRITE;
360
361 aux_head = handle->head;
362 local_set(&rb->aux_head, aux_head);
363 } else {
364 aux_head = local_read(&rb->aux_head);
365 local_add(size, &rb->aux_head);
366 }
367
368 if (size || flags) {
369 /*
370 * Only send RECORD_AUX if we have something useful to communicate
371 */
372
373 perf_event_aux_event(handle->event, aux_head, size, flags);
374 }
375
376 aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);
377
378 if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
379 wakeup = true;
380 local_add(rb->aux_watermark, &rb->aux_wakeup);
381 }
382
383 if (wakeup) {
384 if (truncated)
385 handle->event->pending_disable = 1;
386 perf_output_wakeup(handle);
387 }
388
389 handle->event = NULL;
390
391 local_set(&rb->aux_nest, 0);
392 rb_free_aux(rb);
393 ring_buffer_put_async(rb);
394 }
395
396 /*
397 * Skip over a given number of bytes in the AUX buffer, due to, for example,
398 * hardware's alignment constraints.
399 */
400 int perf_aux_output_skip(struct perf_output_handle *handle, unsigned long size)
401 {
402 struct ring_buffer *rb = handle->rb;
403 unsigned long aux_head;
404
405 if (size > handle->size)
406 return -ENOSPC;
407
408 local_add(size, &rb->aux_head);
409
410 aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);
411 if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
412 perf_output_wakeup(handle);
413 local_add(rb->aux_watermark, &rb->aux_wakeup);
414 handle->wakeup = local_read(&rb->aux_wakeup) +
415 rb->aux_watermark;
416 }
417
418 handle->head = aux_head;
419 handle->size -= size;
420
421 return 0;
422 }
423
424 void *perf_get_aux(struct perf_output_handle *handle)
425 {
426 /* this is only valid between perf_aux_output_begin and *_end */
427 if (!handle->event)
428 return NULL;
429
430 return handle->rb->aux_priv;
431 }
432
433 #define PERF_AUX_GFP (GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY)
434
435 static struct page *rb_alloc_aux_page(int node, int order)
436 {
437 struct page *page;
438
439 if (order > MAX_ORDER)
440 order = MAX_ORDER;
441
442 do {
443 page = alloc_pages_node(node, PERF_AUX_GFP, order);
444 } while (!page && order--);
445
446 if (page && order) {
447 /*
448 * Communicate the allocation size to the driver:
449 * if we managed to secure a high-order allocation,
450 * set its first page's private to this order;
451 * !PagePrivate(page) means it's just a normal page.
452 */
453 split_page(page, order);
454 SetPagePrivate(page);
455 set_page_private(page, order);
456 }
457
458 return page;
459 }
460
461 static void rb_free_aux_page(struct ring_buffer *rb, int idx)
462 {
463 struct page *page = virt_to_page(rb->aux_pages[idx]);
464
465 ClearPagePrivate(page);
466 page->mapping = NULL;
467 __free_page(page);
468 }
469
470 static void __rb_free_aux(struct ring_buffer *rb)
471 {
472 int pg;
473
474 if (rb->aux_priv) {
475 rb->free_aux(rb->aux_priv);
476 rb->free_aux = NULL;
477 rb->aux_priv = NULL;
478 }
479
480 if (rb->aux_nr_pages) {
481 for (pg = 0; pg < rb->aux_nr_pages; pg++)
482 rb_free_aux_page(rb, pg);
483
484 kfree(rb->aux_pages);
485 rb->aux_nr_pages = 0;
486 }
487 }
488
489 int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
490 pgoff_t pgoff, int nr_pages, long watermark, int flags)
491 {
492 bool overwrite = !(flags & RING_BUFFER_WRITABLE);
493 int node = (event->cpu == -1) ? -1 : cpu_to_node(event->cpu);
494 int ret = -ENOMEM, max_order = 0;
495
496 if (!has_aux(event))
497 return -ENOTSUPP;
498
499 if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) {
500 /*
501 * We need to start with the max_order that fits in nr_pages,
502 * not the other way around, hence ilog2() and not get_order.
503 */
504 max_order = ilog2(nr_pages);
505
506 /*
507 * PMU requests more than one contiguous chunks of memory
508 * for SW double buffering
509 */
510 if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_SW_DOUBLEBUF) &&
511 !overwrite) {
512 if (!max_order)
513 return -EINVAL;
514
515 max_order--;
516 }
517 }
518
519 rb->aux_pages = kzalloc_node(nr_pages * sizeof(void *), GFP_KERNEL, node);
520 if (!rb->aux_pages)
521 return -ENOMEM;
522
523 rb->free_aux = event->pmu->free_aux;
524 for (rb->aux_nr_pages = 0; rb->aux_nr_pages < nr_pages;) {
525 struct page *page;
526 int last, order;
527
528 order = min(max_order, ilog2(nr_pages - rb->aux_nr_pages));
529 page = rb_alloc_aux_page(node, order);
530 if (!page)
531 goto out;
532
533 for (last = rb->aux_nr_pages + (1 << page_private(page));
534 last > rb->aux_nr_pages; rb->aux_nr_pages++)
535 rb->aux_pages[rb->aux_nr_pages] = page_address(page++);
536 }
537
538 /*
539 * In overwrite mode, PMUs that don't support SG may not handle more
540 * than one contiguous allocation, since they rely on PMI to do double
541 * buffering. In this case, the entire buffer has to be one contiguous
542 * chunk.
543 */
544 if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) &&
545 overwrite) {
546 struct page *page = virt_to_page(rb->aux_pages[0]);
547
548 if (page_private(page) != max_order)
549 goto out;
550 }
551
552 rb->aux_priv = event->pmu->setup_aux(event->cpu, rb->aux_pages, nr_pages,
553 overwrite);
554 if (!rb->aux_priv)
555 goto out;
556
557 ret = 0;
558
559 /*
560 * aux_pages (and pmu driver's private data, aux_priv) will be
561 * referenced in both producer's and consumer's contexts, thus
562 * we keep a refcount here to make sure either of the two can
563 * reference them safely.
564 */
565 atomic_set(&rb->aux_refcount, 1);
566
567 rb->aux_overwrite = overwrite;
568 rb->aux_watermark = watermark;
569
570 if (!rb->aux_watermark && !rb->aux_overwrite)
571 rb->aux_watermark = nr_pages << (PAGE_SHIFT - 1);
572
573 out:
574 if (!ret)
575 rb->aux_pgoff = pgoff;
576 else
577 __rb_free_aux(rb);
578
579 return ret;
580 }
581
582 void rb_free_aux(struct ring_buffer *rb)
583 {
584 if (atomic_dec_and_test(&rb->aux_refcount))
585 irq_work_queue(&rb->irq_work);
586 }
587
588 static void rb_irq_work(struct irq_work *work)
589 {
590 struct ring_buffer *rb = container_of(work, struct ring_buffer, irq_work);
591
592 if (!atomic_read(&rb->aux_refcount))
593 __rb_free_aux(rb);
594
595 if (rb->rcu_head.next == (void *)rb)
596 call_rcu(&rb->rcu_head, rb_free_rcu);
597 }
598
599 #ifndef CONFIG_PERF_USE_VMALLOC
600
601 /*
602 * Back perf_mmap() with regular GFP_KERNEL-0 pages.
603 */
604
605 static struct page *
606 __perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
607 {
608 if (pgoff > rb->nr_pages)
609 return NULL;
610
611 if (pgoff == 0)
612 return virt_to_page(rb->user_page);
613
614 return virt_to_page(rb->data_pages[pgoff - 1]);
615 }
616
617 static void *perf_mmap_alloc_page(int cpu)
618 {
619 struct page *page;
620 int node;
621
622 node = (cpu == -1) ? cpu : cpu_to_node(cpu);
623 page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
624 if (!page)
625 return NULL;
626
627 return page_address(page);
628 }
629
630 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
631 {
632 struct ring_buffer *rb;
633 unsigned long size;
634 int i;
635
636 size = sizeof(struct ring_buffer);
637 size += nr_pages * sizeof(void *);
638
639 rb = kzalloc(size, GFP_KERNEL);
640 if (!rb)
641 goto fail;
642
643 rb->user_page = perf_mmap_alloc_page(cpu);
644 if (!rb->user_page)
645 goto fail_user_page;
646
647 for (i = 0; i < nr_pages; i++) {
648 rb->data_pages[i] = perf_mmap_alloc_page(cpu);
649 if (!rb->data_pages[i])
650 goto fail_data_pages;
651 }
652
653 rb->nr_pages = nr_pages;
654
655 ring_buffer_init(rb, watermark, flags);
656
657 return rb;
658
659 fail_data_pages:
660 for (i--; i >= 0; i--)
661 free_page((unsigned long)rb->data_pages[i]);
662
663 free_page((unsigned long)rb->user_page);
664
665 fail_user_page:
666 kfree(rb);
667
668 fail:
669 return NULL;
670 }
671
672 static void perf_mmap_free_page(unsigned long addr)
673 {
674 struct page *page = virt_to_page((void *)addr);
675
676 page->mapping = NULL;
677 __free_page(page);
678 }
679
680 void rb_free(struct ring_buffer *rb)
681 {
682 int i;
683
684 perf_mmap_free_page((unsigned long)rb->user_page);
685 for (i = 0; i < rb->nr_pages; i++)
686 perf_mmap_free_page((unsigned long)rb->data_pages[i]);
687 kfree(rb);
688 }
689
690 #else
691 static int data_page_nr(struct ring_buffer *rb)
692 {
693 return rb->nr_pages << page_order(rb);
694 }
695
696 static struct page *
697 __perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
698 {
699 /* The '>' counts in the user page. */
700 if (pgoff > data_page_nr(rb))
701 return NULL;
702
703 return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
704 }
705
706 static void perf_mmap_unmark_page(void *addr)
707 {
708 struct page *page = vmalloc_to_page(addr);
709
710 page->mapping = NULL;
711 }
712
713 static void rb_free_work(struct work_struct *work)
714 {
715 struct ring_buffer *rb;
716 void *base;
717 int i, nr;
718
719 rb = container_of(work, struct ring_buffer, work);
720 nr = data_page_nr(rb);
721
722 base = rb->user_page;
723 /* The '<=' counts in the user page. */
724 for (i = 0; i <= nr; i++)
725 perf_mmap_unmark_page(base + (i * PAGE_SIZE));
726
727 vfree(base);
728 kfree(rb);
729 }
730
731 void rb_free(struct ring_buffer *rb)
732 {
733 schedule_work(&rb->work);
734 }
735
736 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
737 {
738 struct ring_buffer *rb;
739 unsigned long size;
740 void *all_buf;
741
742 size = sizeof(struct ring_buffer);
743 size += sizeof(void *);
744
745 rb = kzalloc(size, GFP_KERNEL);
746 if (!rb)
747 goto fail;
748
749 INIT_WORK(&rb->work, rb_free_work);
750
751 all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
752 if (!all_buf)
753 goto fail_all_buf;
754
755 rb->user_page = all_buf;
756 rb->data_pages[0] = all_buf + PAGE_SIZE;
757 rb->page_order = ilog2(nr_pages);
758 rb->nr_pages = !!nr_pages;
759
760 ring_buffer_init(rb, watermark, flags);
761
762 return rb;
763
764 fail_all_buf:
765 kfree(rb);
766
767 fail:
768 return NULL;
769 }
770
771 #endif
772
773 struct page *
774 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
775 {
776 if (rb->aux_nr_pages) {
777 /* above AUX space */
778 if (pgoff > rb->aux_pgoff + rb->aux_nr_pages)
779 return NULL;
780
781 /* AUX space */
782 if (pgoff >= rb->aux_pgoff)
783 return virt_to_page(rb->aux_pages[pgoff - rb->aux_pgoff]);
784 }
785
786 return __perf_mmap_to_page(rb, pgoff);
787 }
788
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