perf/x86/intel/bts: Add BTS PMU driver

Add support for Branch Trace Store (BTS) via kernel perf event infrastructure.
The difference with the existing implementation of BTS support is that this
one is a separate PMU that exports events' trace buffers to userspace by means
of AUX area of the perf buffer, which is zero-copy mapped into userspace.

The immediate benefit is that the buffer size can be much bigger, resulting in
fewer interrupts and no kernel side copying is involved and little to no trace
data loss. Also, kernel code can be traced with this driver.

The old way of collecting BTS traces still works.
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kaixu Xia <kaixu.xia@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Robert Richter <rric@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@infradead.org
Cc: adrian.hunter@intel.com
Cc: kan.liang@intel.com
Cc: markus.t.metzger@intel.com
Cc: mathieu.poirier@linaro.org
Link: http://lkml.kernel.org/r/1422614435-114702-1-git-send-email-alexander.shishkin@linux.intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/Makefile

@@ -40,7 +40,7 @@ endif
 obj-$(CONFIG_CPU_SUP_INTEL)		+= perf_event_p6.o perf_event_knc.o perf_event_p4.o
 obj-$(CONFIG_CPU_SUP_INTEL)		+= perf_event_intel_lbr.o perf_event_intel_ds.o perf_event_intel.o
 obj-$(CONFIG_CPU_SUP_INTEL)		+= perf_event_intel_rapl.o perf_event_intel_cqm.o
-obj-$(CONFIG_CPU_SUP_INTEL)		+= perf_event_intel_pt.o
+obj-$(CONFIG_CPU_SUP_INTEL)		+= perf_event_intel_pt.o perf_event_intel_bts.o
 
 obj-$(CONFIG_PERF_EVENTS_INTEL_UNCORE)	+= perf_event_intel_uncore.o \
 					   perf_event_intel_uncore_snb.o \

arch/x86/kernel/cpu/perf_event.h

@@ -410,6 +410,7 @@ union x86_pmu_config {
 
 enum {
 	x86_lbr_exclusive_lbr,
+	x86_lbr_exclusive_bts,
 	x86_lbr_exclusive_pt,
 	x86_lbr_exclusive_max,
 };
@@ -810,6 +811,12 @@ int intel_pmu_setup_lbr_filter(struct perf_event *event);
 
 void intel_pt_interrupt(void);
 
+int intel_bts_interrupt(void);
+
+void intel_bts_enable_local(void);
+
+void intel_bts_disable_local(void);
+
 int p4_pmu_init(void);
 
 int p6_pmu_init(void);

arch/x86/kernel/cpu/perf_event_intel.c

@@ -1242,6 +1242,8 @@ static void intel_pmu_disable_all(void)
 
 	if (test_bit(INTEL_PMC_IDX_FIXED_BTS, cpuc->active_mask))
 		intel_pmu_disable_bts();
+	else
+		intel_bts_disable_local();
 
 	intel_pmu_pebs_disable_all();
 	intel_pmu_lbr_disable_all();
@@ -1264,7 +1266,8 @@ static void intel_pmu_enable_all(int added)
 			return;
 
 		intel_pmu_enable_bts(event->hw.config);
-	}
+	} else
+		intel_bts_enable_local();
 }
 
 /*
@@ -1550,6 +1553,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
 		apic_write(APIC_LVTPC, APIC_DM_NMI);
 	intel_pmu_disable_all();
 	handled = intel_pmu_drain_bts_buffer();
+	handled += intel_bts_interrupt();
 	status = intel_pmu_get_status();
 	if (!status)
 		goto done;

arch/x86/kernel/cpu/perf_event_intel_bts.c

+/*
+ * BTS PMU driver for perf
+ * Copyright (c) 2013-2014, Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#undef DEBUG
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/bitops.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/debugfs.h>
+#include <linux/device.h>
+#include <linux/coredump.h>
+
+#include <asm-generic/sizes.h>
+#include <asm/perf_event.h>
+
+#include "perf_event.h"
+
+struct bts_ctx {
+	struct perf_output_handle	handle;
+	struct debug_store		ds_back;
+	int				started;
+};
+
+static DEFINE_PER_CPU(struct bts_ctx, bts_ctx);
+
+#define BTS_RECORD_SIZE		24
+#define BTS_SAFETY_MARGIN	4080
+
+struct bts_phys {
+	struct page	*page;
+	unsigned long	size;
+	unsigned long	offset;
+	unsigned long	displacement;
+};
+
+struct bts_buffer {
+	size_t		real_size;	/* multiple of BTS_RECORD_SIZE */
+	unsigned int	nr_pages;
+	unsigned int	nr_bufs;
+	unsigned int	cur_buf;
+	bool		snapshot;
+	local_t		data_size;
+	local_t		lost;
+	local_t		head;
+	unsigned long	end;
+	void		**data_pages;
+	struct bts_phys	buf[0];
+};
+
+struct pmu bts_pmu;
+
+void intel_pmu_enable_bts(u64 config);
+void intel_pmu_disable_bts(void);
+
+static size_t buf_size(struct page *page)
+{
+	return 1 << (PAGE_SHIFT + page_private(page));
+}
+
+static void *
+bts_buffer_setup_aux(int cpu, void **pages, int nr_pages, bool overwrite)
+{
+	struct bts_buffer *buf;
+	struct page *page;
+	int node = (cpu == -1) ? cpu : cpu_to_node(cpu);
+	unsigned long offset;
+	size_t size = nr_pages << PAGE_SHIFT;
+	int pg, nbuf, pad;
+
+	/* count all the high order buffers */
+	for (pg = 0, nbuf = 0; pg < nr_pages;) {
+		page = virt_to_page(pages[pg]);
+		if (WARN_ON_ONCE(!PagePrivate(page) && nr_pages > 1))
+			return NULL;
+		pg += 1 << page_private(page);
+		nbuf++;
+	}
+
+	/*
+	 * to avoid interrupts in overwrite mode, only allow one physical
+	 */
+	if (overwrite && nbuf > 1)
+		return NULL;
+
+	buf = kzalloc_node(offsetof(struct bts_buffer, buf[nbuf]), GFP_KERNEL, node);
+	if (!buf)
+		return NULL;
+
+	buf->nr_pages = nr_pages;
+	buf->nr_bufs = nbuf;
+	buf->snapshot = overwrite;
+	buf->data_pages = pages;
+	buf->real_size = size - size % BTS_RECORD_SIZE;
+
+	for (pg = 0, nbuf = 0, offset = 0, pad = 0; nbuf < buf->nr_bufs; nbuf++) {
+		unsigned int __nr_pages;
+
+		page = virt_to_page(pages[pg]);
+		__nr_pages = PagePrivate(page) ? 1 << page_private(page) : 1;
+		buf->buf[nbuf].page = page;
+		buf->buf[nbuf].offset = offset;
+		buf->buf[nbuf].displacement = (pad ? BTS_RECORD_SIZE - pad : 0);
+		buf->buf[nbuf].size = buf_size(page) - buf->buf[nbuf].displacement;
+		pad = buf->buf[nbuf].size % BTS_RECORD_SIZE;
+		buf->buf[nbuf].size -= pad;
+
+		pg += __nr_pages;
+		offset += __nr_pages << PAGE_SHIFT;
+	}
+
+	return buf;
+}
+
+static void bts_buffer_free_aux(void *data)
+{
+	kfree(data);
+}
+
+static unsigned long bts_buffer_offset(struct bts_buffer *buf, unsigned int idx)
+{
+	return buf->buf[idx].offset + buf->buf[idx].displacement;
+}
+
+static void
+bts_config_buffer(struct bts_buffer *buf)
+{
+	int cpu = raw_smp_processor_id();
+	struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
+	struct bts_phys *phys = &buf->buf[buf->cur_buf];
+	unsigned long index, thresh = 0, end = phys->size;
+	struct page *page = phys->page;
+
+	index = local_read(&buf->head);
+
+	if (!buf->snapshot) {
+		if (buf->end < phys->offset + buf_size(page))
+			end = buf->end - phys->offset - phys->displacement;
+
+		index -= phys->offset + phys->displacement;
+
+		if (end - index > BTS_SAFETY_MARGIN)
+			thresh = end - BTS_SAFETY_MARGIN;
+		else if (end - index > BTS_RECORD_SIZE)
+			thresh = end - BTS_RECORD_SIZE;
+		else
+			thresh = end;
+	}
+
+	ds->bts_buffer_base = (u64)page_address(page) + phys->displacement;
+	ds->bts_index = ds->bts_buffer_base + index;
+	ds->bts_absolute_maximum = ds->bts_buffer_base + end;
+	ds->bts_interrupt_threshold = !buf->snapshot
+		? ds->bts_buffer_base + thresh
+		: ds->bts_absolute_maximum + BTS_RECORD_SIZE;
+}
+
+static void bts_buffer_pad_out(struct bts_phys *phys, unsigned long head)
+{
+	unsigned long index = head - phys->offset;
+
+	memset(page_address(phys->page) + index, 0, phys->size - index);
+}
+
+static bool bts_buffer_is_full(struct bts_buffer *buf, struct bts_ctx *bts)
+{
+	if (buf->snapshot)
+		return false;
+
+	if (local_read(&buf->data_size) >= bts->handle.size ||
+	    bts->handle.size - local_read(&buf->data_size) < BTS_RECORD_SIZE)
+		return true;
+
+	return false;
+}
+
+static void bts_update(struct bts_ctx *bts)
+{
+	int cpu = raw_smp_processor_id();
+	struct debug_store *ds = per_cpu(cpu_hw_events, cpu).ds;
+	struct bts_buffer *buf = perf_get_aux(&bts->handle);
+	unsigned long index = ds->bts_index - ds->bts_buffer_base, old, head;
+
+	if (!buf)
+		return;
+
+	head = index + bts_buffer_offset(buf, buf->cur_buf);
+	old = local_xchg(&buf->head, head);
+
+	if (!buf->snapshot) {
+		if (old == head)
+			return;
+
+		if (ds->bts_index >= ds->bts_absolute_maximum)
+			local_inc(&buf->lost);
+
+		/*
+		 * old and head are always in the same physical buffer, so we
+		 * can subtract them to get the data size.
+		 */
+		local_add(head - old, &buf->data_size);
+	} else {
+		local_set(&buf->data_size, head);
+	}
+}
+
+static void __bts_event_start(struct perf_event *event)
+{
+	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+	struct bts_buffer *buf = perf_get_aux(&bts->handle);
+	u64 config = 0;
+
+	if (!buf || bts_buffer_is_full(buf, bts))
+		return;
+
+	event->hw.state = 0;
+
+	if (!buf->snapshot)
+		config |= ARCH_PERFMON_EVENTSEL_INT;
+	if (!event->attr.exclude_kernel)
+		config |= ARCH_PERFMON_EVENTSEL_OS;
+	if (!event->attr.exclude_user)
+		config |= ARCH_PERFMON_EVENTSEL_USR;
+
+	bts_config_buffer(buf);
+
+	/*
+	 * local barrier to make sure that ds configuration made it
+	 * before we enable BTS
+	 */
+	wmb();
+
+	intel_pmu_enable_bts(config);
+}
+
+static void bts_event_start(struct perf_event *event, int flags)
+{
+	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+
+	__bts_event_start(event);
+
+	/* PMI handler: this counter is running and likely generating PMIs */
+	ACCESS_ONCE(bts->started) = 1;
+}
+
+static void __bts_event_stop(struct perf_event *event)
+{
+	/*
+	 * No extra synchronization is mandated by the documentation to have
+	 * BTS data stores globally visible.
+	 */
+	intel_pmu_disable_bts();
+
+	if (event->hw.state & PERF_HES_STOPPED)
+		return;
+
+	ACCESS_ONCE(event->hw.state) |= PERF_HES_STOPPED;
+}
+
+static void bts_event_stop(struct perf_event *event, int flags)
+{
+	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+
+	/* PMI handler: don't restart this counter */
+	ACCESS_ONCE(bts->started) = 0;
+
+	__bts_event_stop(event);
+
+	if (flags & PERF_EF_UPDATE)
+		bts_update(bts);
+}
+
+void intel_bts_enable_local(void)
+{
+	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+
+	if (bts->handle.event && bts->started)
+		__bts_event_start(bts->handle.event);
+}
+
+void intel_bts_disable_local(void)
+{
+	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+
+	if (bts->handle.event)
+		__bts_event_stop(bts->handle.event);
+}
+
+static int
+bts_buffer_reset(struct bts_buffer *buf, struct perf_output_handle *handle)
+{
+	unsigned long head, space, next_space, pad, gap, skip, wakeup;
+	unsigned int next_buf;
+	struct bts_phys *phys, *next_phys;
+	int ret;
+
+	if (buf->snapshot)
+		return 0;
+
+	head = handle->head & ((buf->nr_pages << PAGE_SHIFT) - 1);
+	if (WARN_ON_ONCE(head != local_read(&buf->head)))
+		return -EINVAL;
+
+	phys = &buf->buf[buf->cur_buf];
+	space = phys->offset + phys->displacement + phys->size - head;
+	pad = space;
+	if (space > handle->size) {
+		space = handle->size;
+		space -= space % BTS_RECORD_SIZE;
+	}
+	if (space <= BTS_SAFETY_MARGIN) {
+		/* See if next phys buffer has more space */
+		next_buf = buf->cur_buf + 1;
+		if (next_buf >= buf->nr_bufs)
+			next_buf = 0;
+		next_phys = &buf->buf[next_buf];
+		gap = buf_size(phys->page) - phys->displacement - phys->size +
+		      next_phys->displacement;
+		skip = pad + gap;
+		if (handle->size >= skip) {
+			next_space = next_phys->size;
+			if (next_space + skip > handle->size) {
+				next_space = handle->size - skip;
+				next_space -= next_space % BTS_RECORD_SIZE;
+			}
+			if (next_space > space || !space) {
+				if (pad)
+					bts_buffer_pad_out(phys, head);
+				ret = perf_aux_output_skip(handle, skip);
+				if (ret)
+					return ret;
+				/* Advance to next phys buffer */
+				phys = next_phys;
+				space = next_space;
+				head = phys->offset + phys->displacement;
+				/*
+				 * After this, cur_buf and head won't match ds
+				 * anymore, so we must not be racing with
+				 * bts_update().
+				 */
+				buf->cur_buf = next_buf;
+				local_set(&buf->head, head);
+			}
+		}
+	}
+
+	/* Don't go far beyond wakeup watermark */
+	wakeup = BTS_SAFETY_MARGIN + BTS_RECORD_SIZE + handle->wakeup -
+		 handle->head;
+	if (space > wakeup) {
+		space = wakeup;
+		space -= space % BTS_RECORD_SIZE;
+	}
+
+	buf->end = head + space;
+
+	/*
+	 * If we have no space, the lost notification would have been sent when
+	 * we hit absolute_maximum - see bts_update()
+	 */
+	if (!space)
+		return -ENOSPC;
+
+	return 0;
+}
+
+int intel_bts_interrupt(void)
+{
+	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+	struct perf_event *event = bts->handle.event;
+	struct bts_buffer *buf;
+	s64 old_head;
+	int err;
+
+	if (!event || !bts->started)
+		return 0;
+
+	buf = perf_get_aux(&bts->handle);
+	/*
+	 * Skip snapshot counters: they don't use the interrupt, but
+	 * there's no other way of telling, because the pointer will
+	 * keep moving
+	 */
+	if (!buf || buf->snapshot)
+		return 0;
+
+	old_head = local_read(&buf->head);
+	bts_update(bts);
+
+	/* no new data */
+	if (old_head == local_read(&buf->head))
+		return 0;
+
+	perf_aux_output_end(&bts->handle, local_xchg(&buf->data_size, 0),
+			    !!local_xchg(&buf->lost, 0));
+
+	buf = perf_aux_output_begin(&bts->handle, event);
+	if (!buf)
+		return 1;
+
+	err = bts_buffer_reset(buf, &bts->handle);
+	if (err)
+		perf_aux_output_end(&bts->handle, 0, false);
+
+	return 1;
+}
+
+static void bts_event_del(struct perf_event *event, int mode)
+{
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+	struct bts_buffer *buf = perf_get_aux(&bts->handle);
+
+	bts_event_stop(event, PERF_EF_UPDATE);
+
+	if (buf) {
+		if (buf->snapshot)
+			bts->handle.head =
+				local_xchg(&buf->data_size,
+					   buf->nr_pages << PAGE_SHIFT);
+		perf_aux_output_end(&bts->handle, local_xchg(&buf->data_size, 0),
+				    !!local_xchg(&buf->lost, 0));
+	}
+
+	cpuc->ds->bts_index = bts->ds_back.bts_buffer_base;
+	cpuc->ds->bts_buffer_base = bts->ds_back.bts_buffer_base;
+	cpuc->ds->bts_absolute_maximum = bts->ds_back.bts_absolute_maximum;
+	cpuc->ds->bts_interrupt_threshold = bts->ds_back.bts_interrupt_threshold;
+}
+
+static int bts_event_add(struct perf_event *event, int mode)
+{
+	struct bts_buffer *buf;
+	struct bts_ctx *bts = this_cpu_ptr(&bts_ctx);
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	struct hw_perf_event *hwc = &event->hw;
+	int ret = -EBUSY;
+
+	event->hw.state = PERF_HES_STOPPED;
+
+	if (test_bit(INTEL_PMC_IDX_FIXED_BTS, cpuc->active_mask))
+		return -EBUSY;
+
+	if (bts->handle.event)
+		return -EBUSY;
+
+	buf = perf_aux_output_begin(&bts->handle, event);
+	if (!buf)
+		return -EINVAL;
+
+	ret = bts_buffer_reset(buf, &bts->handle);
+	if (ret) {
+		perf_aux_output_end(&bts->handle, 0, false);
+		return ret;
+	}
+
+	bts->ds_back.bts_buffer_base = cpuc->ds->bts_buffer_base;
+	bts->ds_back.bts_absolute_maximum = cpuc->ds->bts_absolute_maximum;
+	bts->ds_back.bts_interrupt_threshold = cpuc->ds->bts_interrupt_threshold;
+
+	if (mode & PERF_EF_START) {
+		bts_event_start(event, 0);
+		if (hwc->state & PERF_HES_STOPPED) {
+			bts_event_del(event, 0);
+			return -EBUSY;
+		}
+	}
+
+	return 0;
+}
+
+static void bts_event_destroy(struct perf_event *event)
+{
+	x86_del_exclusive(x86_lbr_exclusive_bts);
+}
+
+static int bts_event_init(struct perf_event *event)
+{
+	if (event->attr.type != bts_pmu.type)
+		return -ENOENT;
+
+	if (x86_add_exclusive(x86_lbr_exclusive_bts))
+		return -EBUSY;
+
+	event->destroy = bts_event_destroy;
+
+	return 0;
+}
+
+static void bts_event_read(struct perf_event *event)
+{
+}
+
+static __init int bts_init(void)
+{
+	if (!boot_cpu_has(X86_FEATURE_DTES64) || !x86_pmu.bts)
+		return -ENODEV;
+
+	bts_pmu.capabilities	= PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_ITRACE;
+	bts_pmu.task_ctx_nr	= perf_sw_context;
+	bts_pmu.event_init	= bts_event_init;
+	bts_pmu.add		= bts_event_add;
+	bts_pmu.del		= bts_event_del;
+	bts_pmu.start		= bts_event_start;
+	bts_pmu.stop		= bts_event_stop;
+	bts_pmu.read		= bts_event_read;
+	bts_pmu.setup_aux	= bts_buffer_setup_aux;
+	bts_pmu.free_aux	= bts_buffer_free_aux;
+
+	return perf_pmu_register(&bts_pmu, "intel_bts", -1);
+}
+
+module_init(bts_init);

arch/x86/kernel/cpu/perf_event_intel_ds.c

@@ -461,7 +461,8 @@ void intel_pmu_enable_bts(u64 config)
 
 	debugctlmsr |= DEBUGCTLMSR_TR;
 	debugctlmsr |= DEBUGCTLMSR_BTS;
-	debugctlmsr |= DEBUGCTLMSR_BTINT;
+	if (config & ARCH_PERFMON_EVENTSEL_INT)
+		debugctlmsr |= DEBUGCTLMSR_BTINT;
 
 	if (!(config & ARCH_PERFMON_EVENTSEL_OS))
 		debugctlmsr |= DEBUGCTLMSR_BTS_OFF_OS;