xref: /linux/arch/x86/events/intel/bts.c (revision 3a39d672e7f48b8d6b91a09afa4b55352773b4b5)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * BTS PMU driver for perf
4  * Copyright (c) 2013-2014, Intel Corporation.
5  */
6 
7 #undef DEBUG
8 
9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10 
11 #include <linux/bitops.h>
12 #include <linux/types.h>
13 #include <linux/slab.h>
14 #include <linux/debugfs.h>
15 #include <linux/device.h>
16 #include <linux/coredump.h>
17 
18 #include <linux/sizes.h>
19 #include <asm/perf_event.h>
20 
21 #include "../perf_event.h"
22 
23 struct bts_ctx {
24 	struct perf_output_handle	handle;
25 	struct debug_store		ds_back;
26 	int				state;
27 };
28 
29 /* BTS context states: */
30 enum {
31 	/* no ongoing AUX transactions */
32 	BTS_STATE_STOPPED = 0,
33 	/* AUX transaction is on, BTS tracing is disabled */
34 	BTS_STATE_INACTIVE,
35 	/* AUX transaction is on, BTS tracing is running */
36 	BTS_STATE_ACTIVE,
37 };
38 
39 static DEFINE_PER_CPU(struct bts_ctx, bts_ctx);
40 
41 #define BTS_RECORD_SIZE		24
42 #define BTS_SAFETY_MARGIN	4080
43 
44 struct bts_phys {
45 	struct page	*page;
46 	unsigned long	size;
47 	unsigned long	offset;
48 	unsigned long	displacement;
49 };
50 
51 struct bts_buffer {
52 	size_t		real_size;	/* multiple of BTS_RECORD_SIZE */
53 	unsigned int	nr_pages;
54 	unsigned int	nr_bufs;
55 	unsigned int	cur_buf;
56 	bool		snapshot;
57 	local_t		data_size;
58 	local_t		head;
59 	unsigned long	end;
60 	void		**data_pages;
61 	struct bts_phys	buf[];
62 };
63 
64 static struct pmu bts_pmu;
65 
buf_nr_pages(struct page * page)66 static int buf_nr_pages(struct page *page)
67 {
68 	if (!PagePrivate(page))
69 		return 1;
70 
71 	return 1 << page_private(page);
72 }
73 
buf_size(struct page * page)74 static size_t buf_size(struct page *page)
75 {
76 	return buf_nr_pages(page) * PAGE_SIZE;
77 }
78 
79 static void *
bts_buffer_setup_aux(struct perf_event * event,void ** pages,int nr_pages,bool overwrite)80 bts_buffer_setup_aux(struct perf_event *event, void **pages,
81 		     int nr_pages, bool overwrite)
82 {
83 	struct bts_buffer *buf;
84 	struct page *page;
85 	int cpu = event->cpu;
86 	int node = (cpu == -1) ? cpu : cpu_to_node(cpu);
87 	unsigned long offset;
88 	size_t size = nr_pages << PAGE_SHIFT;
89 	int pg, nbuf, pad;
90 
91 	/* count all the high order buffers */
92 	for (pg = 0, nbuf = 0; pg < nr_pages;) {
93 		page = virt_to_page(pages[pg]);
94 		pg += buf_nr_pages(page);
95 		nbuf++;
96 	}
97 
98 	/*
99 	 * to avoid interrupts in overwrite mode, only allow one physical
100 	 */
101 	if (overwrite && nbuf > 1)
102 		return NULL;
103 
104 	buf = kzalloc_node(offsetof(struct bts_buffer, buf[nbuf]), GFP_KERNEL, node);
105 	if (!buf)
106 		return NULL;
107 
108 	buf->nr_pages = nr_pages;
109 	buf->nr_bufs = nbuf;
110 	buf->snapshot = overwrite;
111 	buf->data_pages = pages;
112 	buf->real_size = size - size % BTS_RECORD_SIZE;
113 
114 	for (pg = 0, nbuf = 0, offset = 0, pad = 0; nbuf < buf->nr_bufs; nbuf++) {
115 		unsigned int __nr_pages;
116 
117 		page = virt_to_page(pages[pg]);
118 		__nr_pages = buf_nr_pages(page);
119 		buf->buf[nbuf].page = page;
120 		buf->buf[nbuf].offset = offset;
121 		buf->buf[nbuf].displacement = (pad ? BTS_RECORD_SIZE - pad : 0);
122 		buf->buf[nbuf].size = buf_size(page) - buf->buf[nbuf].displacement;
123 		pad = buf->buf[nbuf].size % BTS_RECORD_SIZE;
124 		buf->buf[nbuf].size -= pad;
125 
126 		pg += __nr_pages;
127 		offset += __nr_pages << PAGE_SHIFT;
128 	}
129 
130 	return buf;
131 }
132 
bts_buffer_free_aux(void * data)133 static void bts_buffer_free_aux(void *data)
134 {
135 	kfree(data);
136 }
137 
bts_buffer_offset(struct bts_buffer * buf,unsigned int idx)138 static unsigned long bts_buffer_offset(struct bts_buffer *buf, unsigned int idx)
139 {
140 	return buf->buf[idx].offset + buf->buf[idx].displacement;
141 }
142 
143 static void
bts_config_buffer(struct bts_buffer * buf)144 bts_config_buffer(struct bts_buffer *buf)
145 {
146 	int cpu = raw_smp_processor_id();
147 	struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
148 	struct bts_phys *phys = &buf->buf[buf->cur_buf];
149 	unsigned long index, thresh = 0, end = phys->size;
150 	struct page *page = phys->page;
151 
152 	index = local_read(&buf->head);
153 
154 	if (!buf->snapshot) {
155 		if (buf->end < phys->offset + buf_size(page))
156 			end = buf->end - phys->offset - phys->displacement;
157 
158 		index -= phys->offset + phys->displacement;
159 
160 		if (end - index > BTS_SAFETY_MARGIN)
161 			thresh = end - BTS_SAFETY_MARGIN;
162 		else if (end - index > BTS_RECORD_SIZE)
163 			thresh = end - BTS_RECORD_SIZE;
164 		else
165 			thresh = end;
166 	}
167 
168 	ds->bts_buffer_base = (u64)(long)page_address(page) + phys->displacement;
169 	ds->bts_index = ds->bts_buffer_base + index;
170 	ds->bts_absolute_maximum = ds->bts_buffer_base + end;
171 	ds->bts_interrupt_threshold = !buf->snapshot
172 		? ds->bts_buffer_base + thresh
173 		: ds->bts_absolute_maximum + BTS_RECORD_SIZE;
174 }
175 
bts_buffer_pad_out(struct bts_phys * phys,unsigned long head)176 static void bts_buffer_pad_out(struct bts_phys *phys, unsigned long head)
177 {
178 	unsigned long index = head - phys->offset;
179 
180 	memset(page_address(phys->page) + index, 0, phys->size - index);
181 }
182 
bts_update(struct bts_ctx * bts)183 static void bts_update(struct bts_ctx *bts)
184 {
185 	int cpu = raw_smp_processor_id();
186 	struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
187 	struct bts_buffer *buf = perf_get_aux(&bts->handle);
188 	unsigned long index = ds->bts_index - ds->bts_buffer_base, old, head;
189 
190 	if (!buf)
191 		return;
192 
193 	head = index + bts_buffer_offset(buf, buf->cur_buf);
194 	old = local_xchg(&buf->head, head);
195 
196 	if (!buf->snapshot) {
197 		if (old == head)
198 			return;
199 
200 		if (ds->bts_index >= ds->bts_absolute_maximum)
201 			perf_aux_output_flag(&bts->handle,
202 			                     PERF_AUX_FLAG_TRUNCATED);
203 
204 		/*
205 		 * old and head are always in the same physical buffer, so we
206 		 * can subtract them to get the data size.
207 		 */
208 		local_add(head - old, &buf->data_size);
209 	} else {
210 		local_set(&buf->data_size, head);
211 	}
212 
213 	/*
214 	 * Since BTS is coherent, just add compiler barrier to ensure
215 	 * BTS updating is ordered against bts::handle::event.
216 	 */
217 	barrier();
218 }
219 
220 static int
221 bts_buffer_reset(struct bts_buffer *buf, struct perf_output_handle *handle);
222 
223 /*
224  * Ordering PMU callbacks wrt themselves and the PMI is done by means
225  * of bts::state, which:
226  *  - is set when bts::handle::event is valid, that is, between
227  *    perf_aux_output_begin() and perf_aux_output_end();
228  *  - is zero otherwise;
229  *  - is ordered against bts::handle::event with a compiler barrier.
230  */
231 
__bts_event_start(struct perf_event * event)232 static void __bts_event_start(struct perf_event *event)
233 {
234 	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
235 	struct bts_buffer *buf = perf_get_aux(&bts->handle);
236 	u64 config = 0;
237 
238 	if (!buf->snapshot)
239 		config |= ARCH_PERFMON_EVENTSEL_INT;
240 	if (!event->attr.exclude_kernel)
241 		config |= ARCH_PERFMON_EVENTSEL_OS;
242 	if (!event->attr.exclude_user)
243 		config |= ARCH_PERFMON_EVENTSEL_USR;
244 
245 	bts_config_buffer(buf);
246 
247 	/*
248 	 * local barrier to make sure that ds configuration made it
249 	 * before we enable BTS and bts::state goes ACTIVE
250 	 */
251 	wmb();
252 
253 	/* INACTIVE/STOPPED -> ACTIVE */
254 	WRITE_ONCE(bts->state, BTS_STATE_ACTIVE);
255 
256 	intel_pmu_enable_bts(config);
257 
258 }
259 
bts_event_start(struct perf_event * event,int flags)260 static void bts_event_start(struct perf_event *event, int flags)
261 {
262 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
263 	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
264 	struct bts_buffer *buf;
265 
266 	buf = perf_aux_output_begin(&bts->handle, event);
267 	if (!buf)
268 		goto fail_stop;
269 
270 	if (bts_buffer_reset(buf, &bts->handle))
271 		goto fail_end_stop;
272 
273 	bts->ds_back.bts_buffer_base = cpuc->ds->bts_buffer_base;
274 	bts->ds_back.bts_absolute_maximum = cpuc->ds->bts_absolute_maximum;
275 	bts->ds_back.bts_interrupt_threshold = cpuc->ds->bts_interrupt_threshold;
276 
277 	perf_event_itrace_started(event);
278 	event->hw.state = 0;
279 
280 	__bts_event_start(event);
281 
282 	return;
283 
284 fail_end_stop:
285 	perf_aux_output_end(&bts->handle, 0);
286 
287 fail_stop:
288 	event->hw.state = PERF_HES_STOPPED;
289 }
290 
__bts_event_stop(struct perf_event * event,int state)291 static void __bts_event_stop(struct perf_event *event, int state)
292 {
293 	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
294 
295 	/* ACTIVE -> INACTIVE(PMI)/STOPPED(->stop()) */
296 	WRITE_ONCE(bts->state, state);
297 
298 	/*
299 	 * No extra synchronization is mandated by the documentation to have
300 	 * BTS data stores globally visible.
301 	 */
302 	intel_pmu_disable_bts();
303 }
304 
bts_event_stop(struct perf_event * event,int flags)305 static void bts_event_stop(struct perf_event *event, int flags)
306 {
307 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
308 	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
309 	struct bts_buffer *buf = NULL;
310 	int state = READ_ONCE(bts->state);
311 
312 	if (state == BTS_STATE_ACTIVE)
313 		__bts_event_stop(event, BTS_STATE_STOPPED);
314 
315 	if (state != BTS_STATE_STOPPED)
316 		buf = perf_get_aux(&bts->handle);
317 
318 	event->hw.state |= PERF_HES_STOPPED;
319 
320 	if (flags & PERF_EF_UPDATE) {
321 		bts_update(bts);
322 
323 		if (buf) {
324 			if (buf->snapshot)
325 				bts->handle.head =
326 					local_xchg(&buf->data_size,
327 						   buf->nr_pages << PAGE_SHIFT);
328 			perf_aux_output_end(&bts->handle,
329 			                    local_xchg(&buf->data_size, 0));
330 		}
331 
332 		cpuc->ds->bts_index = bts->ds_back.bts_buffer_base;
333 		cpuc->ds->bts_buffer_base = bts->ds_back.bts_buffer_base;
334 		cpuc->ds->bts_absolute_maximum = bts->ds_back.bts_absolute_maximum;
335 		cpuc->ds->bts_interrupt_threshold = bts->ds_back.bts_interrupt_threshold;
336 	}
337 }
338 
intel_bts_enable_local(void)339 void intel_bts_enable_local(void)
340 {
341 	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
342 	int state = READ_ONCE(bts->state);
343 
344 	/*
345 	 * Here we transition from INACTIVE to ACTIVE;
346 	 * if we instead are STOPPED from the interrupt handler,
347 	 * stay that way. Can't be ACTIVE here though.
348 	 */
349 	if (WARN_ON_ONCE(state == BTS_STATE_ACTIVE))
350 		return;
351 
352 	if (state == BTS_STATE_STOPPED)
353 		return;
354 
355 	if (bts->handle.event)
356 		__bts_event_start(bts->handle.event);
357 }
358 
intel_bts_disable_local(void)359 void intel_bts_disable_local(void)
360 {
361 	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
362 
363 	/*
364 	 * Here we transition from ACTIVE to INACTIVE;
365 	 * do nothing for STOPPED or INACTIVE.
366 	 */
367 	if (READ_ONCE(bts->state) != BTS_STATE_ACTIVE)
368 		return;
369 
370 	if (bts->handle.event)
371 		__bts_event_stop(bts->handle.event, BTS_STATE_INACTIVE);
372 }
373 
374 static int
bts_buffer_reset(struct bts_buffer * buf,struct perf_output_handle * handle)375 bts_buffer_reset(struct bts_buffer *buf, struct perf_output_handle *handle)
376 {
377 	unsigned long head, space, next_space, pad, gap, skip, wakeup;
378 	unsigned int next_buf;
379 	struct bts_phys *phys, *next_phys;
380 	int ret;
381 
382 	if (buf->snapshot)
383 		return 0;
384 
385 	head = handle->head & ((buf->nr_pages << PAGE_SHIFT) - 1);
386 
387 	phys = &buf->buf[buf->cur_buf];
388 	space = phys->offset + phys->displacement + phys->size - head;
389 	pad = space;
390 	if (space > handle->size) {
391 		space = handle->size;
392 		space -= space % BTS_RECORD_SIZE;
393 	}
394 	if (space <= BTS_SAFETY_MARGIN) {
395 		/* See if next phys buffer has more space */
396 		next_buf = buf->cur_buf + 1;
397 		if (next_buf >= buf->nr_bufs)
398 			next_buf = 0;
399 		next_phys = &buf->buf[next_buf];
400 		gap = buf_size(phys->page) - phys->displacement - phys->size +
401 		      next_phys->displacement;
402 		skip = pad + gap;
403 		if (handle->size >= skip) {
404 			next_space = next_phys->size;
405 			if (next_space + skip > handle->size) {
406 				next_space = handle->size - skip;
407 				next_space -= next_space % BTS_RECORD_SIZE;
408 			}
409 			if (next_space > space || !space) {
410 				if (pad)
411 					bts_buffer_pad_out(phys, head);
412 				ret = perf_aux_output_skip(handle, skip);
413 				if (ret)
414 					return ret;
415 				/* Advance to next phys buffer */
416 				phys = next_phys;
417 				space = next_space;
418 				head = phys->offset + phys->displacement;
419 				/*
420 				 * After this, cur_buf and head won't match ds
421 				 * anymore, so we must not be racing with
422 				 * bts_update().
423 				 */
424 				buf->cur_buf = next_buf;
425 				local_set(&buf->head, head);
426 			}
427 		}
428 	}
429 
430 	/* Don't go far beyond wakeup watermark */
431 	wakeup = BTS_SAFETY_MARGIN + BTS_RECORD_SIZE + handle->wakeup -
432 		 handle->head;
433 	if (space > wakeup) {
434 		space = wakeup;
435 		space -= space % BTS_RECORD_SIZE;
436 	}
437 
438 	buf->end = head + space;
439 
440 	/*
441 	 * If we have no space, the lost notification would have been sent when
442 	 * we hit absolute_maximum - see bts_update()
443 	 */
444 	if (!space)
445 		return -ENOSPC;
446 
447 	return 0;
448 }
449 
intel_bts_interrupt(void)450 int intel_bts_interrupt(void)
451 {
452 	struct debug_store *ds = this_cpu_ptr(&cpu_hw_events)->ds;
453 	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
454 	struct perf_event *event = bts->handle.event;
455 	struct bts_buffer *buf;
456 	s64 old_head;
457 	int err = -ENOSPC, handled = 0;
458 
459 	/*
460 	 * The only surefire way of knowing if this NMI is ours is by checking
461 	 * the write ptr against the PMI threshold.
462 	 */
463 	if (ds && (ds->bts_index >= ds->bts_interrupt_threshold))
464 		handled = 1;
465 
466 	/*
467 	 * this is wrapped in intel_bts_enable_local/intel_bts_disable_local,
468 	 * so we can only be INACTIVE or STOPPED
469 	 */
470 	if (READ_ONCE(bts->state) == BTS_STATE_STOPPED)
471 		return handled;
472 
473 	buf = perf_get_aux(&bts->handle);
474 	if (!buf)
475 		return handled;
476 
477 	/*
478 	 * Skip snapshot counters: they don't use the interrupt, but
479 	 * there's no other way of telling, because the pointer will
480 	 * keep moving
481 	 */
482 	if (buf->snapshot)
483 		return 0;
484 
485 	old_head = local_read(&buf->head);
486 	bts_update(bts);
487 
488 	/* no new data */
489 	if (old_head == local_read(&buf->head))
490 		return handled;
491 
492 	perf_aux_output_end(&bts->handle, local_xchg(&buf->data_size, 0));
493 
494 	buf = perf_aux_output_begin(&bts->handle, event);
495 	if (buf)
496 		err = bts_buffer_reset(buf, &bts->handle);
497 
498 	if (err) {
499 		WRITE_ONCE(bts->state, BTS_STATE_STOPPED);
500 
501 		if (buf) {
502 			/*
503 			 * BTS_STATE_STOPPED should be visible before
504 			 * cleared handle::event
505 			 */
506 			barrier();
507 			perf_aux_output_end(&bts->handle, 0);
508 		}
509 	}
510 
511 	return 1;
512 }
513 
bts_event_del(struct perf_event * event,int mode)514 static void bts_event_del(struct perf_event *event, int mode)
515 {
516 	bts_event_stop(event, PERF_EF_UPDATE);
517 }
518 
bts_event_add(struct perf_event * event,int mode)519 static int bts_event_add(struct perf_event *event, int mode)
520 {
521 	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
522 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
523 	struct hw_perf_event *hwc = &event->hw;
524 
525 	event->hw.state = PERF_HES_STOPPED;
526 
527 	if (test_bit(INTEL_PMC_IDX_FIXED_BTS, cpuc->active_mask))
528 		return -EBUSY;
529 
530 	if (bts->handle.event)
531 		return -EBUSY;
532 
533 	if (mode & PERF_EF_START) {
534 		bts_event_start(event, 0);
535 		if (hwc->state & PERF_HES_STOPPED)
536 			return -EINVAL;
537 	}
538 
539 	return 0;
540 }
541 
bts_event_destroy(struct perf_event * event)542 static void bts_event_destroy(struct perf_event *event)
543 {
544 	x86_release_hardware();
545 	x86_del_exclusive(x86_lbr_exclusive_bts);
546 }
547 
bts_event_init(struct perf_event * event)548 static int bts_event_init(struct perf_event *event)
549 {
550 	int ret;
551 
552 	if (event->attr.type != bts_pmu.type)
553 		return -ENOENT;
554 
555 	/*
556 	 * BTS leaks kernel addresses even when CPL0 tracing is
557 	 * disabled, so disallow intel_bts driver for unprivileged
558 	 * users on paranoid systems since it provides trace data
559 	 * to the user in a zero-copy fashion.
560 	 */
561 	if (event->attr.exclude_kernel) {
562 		ret = perf_allow_kernel(&event->attr);
563 		if (ret)
564 			return ret;
565 	}
566 
567 	if (x86_add_exclusive(x86_lbr_exclusive_bts))
568 		return -EBUSY;
569 
570 	ret = x86_reserve_hardware();
571 	if (ret) {
572 		x86_del_exclusive(x86_lbr_exclusive_bts);
573 		return ret;
574 	}
575 
576 	event->destroy = bts_event_destroy;
577 
578 	return 0;
579 }
580 
bts_event_read(struct perf_event * event)581 static void bts_event_read(struct perf_event *event)
582 {
583 }
584 
bts_init(void)585 static __init int bts_init(void)
586 {
587 	if (!boot_cpu_has(X86_FEATURE_DTES64) || !x86_pmu.bts)
588 		return -ENODEV;
589 
590 	if (boot_cpu_has(X86_FEATURE_PTI)) {
591 		/*
592 		 * BTS hardware writes through a virtual memory map we must
593 		 * either use the kernel physical map, or the user mapping of
594 		 * the AUX buffer.
595 		 *
596 		 * However, since this driver supports per-CPU and per-task inherit
597 		 * we cannot use the user mapping since it will not be available
598 		 * if we're not running the owning process.
599 		 *
600 		 * With PTI we can't use the kernel map either, because its not
601 		 * there when we run userspace.
602 		 *
603 		 * For now, disable this driver when using PTI.
604 		 */
605 		return -ENODEV;
606 	}
607 
608 	bts_pmu.capabilities	= PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_ITRACE |
609 				  PERF_PMU_CAP_EXCLUSIVE;
610 	bts_pmu.task_ctx_nr	= perf_sw_context;
611 	bts_pmu.event_init	= bts_event_init;
612 	bts_pmu.add		= bts_event_add;
613 	bts_pmu.del		= bts_event_del;
614 	bts_pmu.start		= bts_event_start;
615 	bts_pmu.stop		= bts_event_stop;
616 	bts_pmu.read		= bts_event_read;
617 	bts_pmu.setup_aux	= bts_buffer_setup_aux;
618 	bts_pmu.free_aux	= bts_buffer_free_aux;
619 
620 	return perf_pmu_register(&bts_pmu, "intel_bts", -1);
621 }
622 arch_initcall(bts_init);
623