x86, ptrace: support for branch trace store(BTS)

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Changes to the last version:
- split implementation into two layers: ds/bts and ptrace
- renamed TIF's
- save/restore ds save area msr in __switch_to_xtra()
- make block-stepping only look at BTF bit

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/Makefile_32

@@ -11,6 +11,7 @@ obj-y	:= process_32.o signal_32.o entry_32.o traps_32.o irq_32.o \
 		quirks.o i8237.o topology.o alternative.o i8253.o tsc_32.o io_delay.o rtc.o
 
 obj-y				+= ptrace.o
+obj-y				+= ds.o
 obj-y				+= tls.o
 obj-y				+= step.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o

arch/x86/kernel/Makefile_64

@@ -13,6 +13,7 @@ obj-y	:= process_64.o signal_64.o entry_64.o traps_64.o irq_64.o \
 		i8253.o io_delay.o rtc.o
 
 obj-y				+= ptrace.o
+obj-y				+= ds.o
 obj-y				+= step.o
 
 obj-$(CONFIG_IA32_EMULATION)	+= tls.o

arch/x86/kernel/cpu/intel.c

@@ -11,6 +11,8 @@
 #include <asm/pgtable.h>
 #include <asm/msr.h>
 #include <asm/uaccess.h>
+#include <asm/ptrace.h>
+#include <asm/ds.h>
 
 #include "cpu.h"
 
@@ -219,6 +221,9 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
 		if (!(l1 & (1<<12)))
 			set_bit(X86_FEATURE_PEBS, c->x86_capability);
 	}
+
+	if (cpu_has_bts)
+		ds_init_intel(c);
 }
 
 static unsigned int __cpuinit intel_size_cache(struct cpuinfo_x86 * c, unsigned int size)

arch/x86/kernel/ds.c

@@ -0,0 +1,429 @@
+/*
+ * Debug Store support
+ *
+ * This provides a low-level interface to the hardware's Debug Store
+ * feature that is used for last branch recording (LBR) and
+ * precise-event based sampling (PEBS).
+ *
+ * Different architectures use a different DS layout/pointer size.
+ * The below functions therefore work on a void*.
+ *
+ *
+ * Since there is no user for PEBS, yet, only LBR (or branch
+ * trace store, BTS) is supported.
+ *
+ *
+ * Copyright (C) 2007 Intel Corporation.
+ * Markus Metzger <markus.t.metzger@intel.com>, Dec 2007
+ */
+
+#include <asm/ds.h>
+
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+
+
+/*
+ * Debug Store (DS) save area configuration (see Intel64 and IA32
+ * Architectures Software Developer's Manual, section 18.5)
+ *
+ * The DS configuration consists of the following fields; different
+ * architetures vary in the size of those fields.
+ * - double-word aligned base linear address of the BTS buffer
+ * - write pointer into the BTS buffer
+ * - end linear address of the BTS buffer (one byte beyond the end of
+ *   the buffer)
+ * - interrupt pointer into BTS buffer
+ *   (interrupt occurs when write pointer passes interrupt pointer)
+ * - double-word aligned base linear address of the PEBS buffer
+ * - write pointer into the PEBS buffer
+ * - end linear address of the PEBS buffer (one byte beyond the end of
+ *   the buffer)
+ * - interrupt pointer into PEBS buffer
+ *   (interrupt occurs when write pointer passes interrupt pointer)
+ * - value to which counter is reset following counter overflow
+ *
+ * On later architectures, the last branch recording hardware uses
+ * 64bit pointers even in 32bit mode.
+ *
+ *
+ * Branch Trace Store (BTS) records store information about control
+ * flow changes. They at least provide the following information:
+ * - source linear address
+ * - destination linear address
+ *
+ * Netburst supported a predicated bit that had been dropped in later
+ * architectures. We do not suppor it.
+ *
+ *
+ * In order to abstract from the actual DS and BTS layout, we describe
+ * the access to the relevant fields.
+ * Thanks to Andi Kleen for proposing this design.
+ *
+ * The implementation, however, is not as general as it might seem. In
+ * order to stay somewhat simple and efficient, we assume an
+ * underlying unsigned type (mostly a pointer type) and we expect the
+ * field to be at least as big as that type.
+ */
+
+/*
+ * A special from_ip address to indicate that the BTS record is an
+ * info record that needs to be interpreted or skipped.
+ */
+#define BTS_ESCAPE_ADDRESS (-1)
+
+/*
+ * A field access descriptor
+ */
+struct access_desc {
+	unsigned char offset;
+	unsigned char size;
+};
+
+/*
+ * The configuration for a particular DS/BTS hardware implementation.
+ */
+struct ds_configuration {
+	/* the DS configuration */
+	unsigned char  sizeof_ds;
+	struct access_desc bts_buffer_base;
+	struct access_desc bts_index;
+	struct access_desc bts_absolute_maximum;
+	struct access_desc bts_interrupt_threshold;
+	/* the BTS configuration */
+	unsigned char  sizeof_bts;
+	struct access_desc from_ip;
+	struct access_desc to_ip;
+	/* BTS variants used to store additional information like
+	   timestamps */
+	struct access_desc info_type;
+	struct access_desc info_data;
+	unsigned long debugctl_mask;
+};
+
+/*
+ * The global configuration used by the below accessor functions
+ */
+static struct ds_configuration ds_cfg;
+
+/*
+ * Accessor functions for some DS and BTS fields using the above
+ * global ptrace_bts_cfg.
+ */
+static inline void *get_bts_buffer_base(char *base)
+{
+	return *(void **)(base + ds_cfg.bts_buffer_base.offset);
+}
+static inline void set_bts_buffer_base(char *base, void *value)
+{
+	(*(void **)(base + ds_cfg.bts_buffer_base.offset)) = value;
+}
+static inline void *get_bts_index(char *base)
+{
+	return *(void **)(base + ds_cfg.bts_index.offset);
+}
+static inline void set_bts_index(char *base, void *value)
+{
+	(*(void **)(base + ds_cfg.bts_index.offset)) = value;
+}
+static inline void *get_bts_absolute_maximum(char *base)
+{
+	return *(void **)(base + ds_cfg.bts_absolute_maximum.offset);
+}
+static inline void set_bts_absolute_maximum(char *base, void *value)
+{
+	(*(void **)(base + ds_cfg.bts_absolute_maximum.offset)) = value;
+}
+static inline void *get_bts_interrupt_threshold(char *base)
+{
+	return *(void **)(base + ds_cfg.bts_interrupt_threshold.offset);
+}
+static inline void set_bts_interrupt_threshold(char *base, void *value)
+{
+	(*(void **)(base + ds_cfg.bts_interrupt_threshold.offset)) = value;
+}
+static inline long get_from_ip(char *base)
+{
+	return *(long *)(base + ds_cfg.from_ip.offset);
+}
+static inline void set_from_ip(char *base, long value)
+{
+	(*(long *)(base + ds_cfg.from_ip.offset)) = value;
+}
+static inline long get_to_ip(char *base)
+{
+	return *(long *)(base + ds_cfg.to_ip.offset);
+}
+static inline void set_to_ip(char *base, long value)
+{
+	(*(long *)(base + ds_cfg.to_ip.offset)) = value;
+}
+static inline unsigned char get_info_type(char *base)
+{
+	return *(unsigned char *)(base + ds_cfg.info_type.offset);
+}
+static inline void set_info_type(char *base, unsigned char value)
+{
+	(*(unsigned char *)(base + ds_cfg.info_type.offset)) = value;
+}
+/*
+ * The info data might overlap with the info type on some architectures.
+ * We therefore read and write the exact number of bytes.
+ */
+static inline unsigned long long get_info_data(char *base)
+{
+	unsigned long long value = 0;
+	memcpy(&value,
+	       base + ds_cfg.info_data.offset,
+	       ds_cfg.info_data.size);
+	return value;
+}
+static inline void set_info_data(char *base, unsigned long long value)
+{
+	memcpy(base + ds_cfg.info_data.offset,
+	       &value,
+	       ds_cfg.info_data.size);
+}
+
+
+int ds_allocate(void **dsp, size_t bts_size_in_records)
+{
+	size_t bts_size_in_bytes = 0;
+	void *bts = 0;
+	void *ds = 0;
+
+	if (!ds_cfg.sizeof_ds || !ds_cfg.sizeof_bts)
+		return -EOPNOTSUPP;
+
+	if (bts_size_in_records < 0)
+		return -EINVAL;
+
+	bts_size_in_bytes =
+		bts_size_in_records * ds_cfg.sizeof_bts;
+
+	if (bts_size_in_bytes <= 0)
+		return -EINVAL;
+
+	bts = kzalloc(bts_size_in_bytes, GFP_KERNEL);
+
+	if (!bts)
+		return -ENOMEM;
+
+	ds = kzalloc(ds_cfg.sizeof_ds, GFP_KERNEL);
+
+	if (!ds) {
+		kfree(bts);
+		return -ENOMEM;
+	}
+
+	set_bts_buffer_base(ds, bts);
+	set_bts_index(ds, bts);
+	set_bts_absolute_maximum(ds, bts + bts_size_in_bytes);
+	set_bts_interrupt_threshold(ds, bts + bts_size_in_bytes + 1);
+
+	*dsp = ds;
+	return 0;
+}
+
+int ds_free(void **dsp)
+{
+	if (*dsp)
+		kfree(get_bts_buffer_base(*dsp));
+	kfree(*dsp);
+	*dsp = 0;
+
+	return 0;
+}
+
+int ds_get_bts_size(void *ds)
+{
+	size_t size_in_bytes;
+
+	if (!ds_cfg.sizeof_ds || !ds_cfg.sizeof_bts)
+		return -EOPNOTSUPP;
+
+	size_in_bytes =
+		get_bts_absolute_maximum(ds) -
+		get_bts_buffer_base(ds);
+
+	return size_in_bytes / ds_cfg.sizeof_bts;
+}
+
+int ds_get_bts_index(void *ds)
+{
+	size_t index_offset_in_bytes;
+
+	if (!ds_cfg.sizeof_ds || !ds_cfg.sizeof_bts)
+		return -EOPNOTSUPP;
+
+	index_offset_in_bytes =
+		get_bts_index(ds) -
+		get_bts_buffer_base(ds);
+
+	return index_offset_in_bytes / ds_cfg.sizeof_bts;
+}
+
+int ds_read_bts(void *ds, size_t index, struct bts_struct *out)
+{
+	void *bts;
+
+	if (!ds_cfg.sizeof_ds || !ds_cfg.sizeof_bts)
+		return -EOPNOTSUPP;
+
+	if (index < 0)
+		return -EINVAL;
+
+	if (index >= ds_get_bts_size(ds))
+		return -EINVAL;
+
+	bts = get_bts_buffer_base(ds);
+	bts = (char *)bts + (index * ds_cfg.sizeof_bts);
+
+	memset(out, 0, sizeof(*out));
+	if (get_from_ip(bts) == BTS_ESCAPE_ADDRESS) {
+		out->qualifier         = get_info_type(bts);
+		out->variant.timestamp = get_info_data(bts);
+	} else {
+		out->qualifier = BTS_BRANCH;
+		out->variant.lbr.from_ip = get_from_ip(bts);
+		out->variant.lbr.to_ip   = get_to_ip(bts);
+	}
+
+	return 0;
+}
+
+int ds_write_bts(void *ds, const struct bts_struct *in)
+{
+	void *bts;
+
+	if (!ds_cfg.sizeof_ds || !ds_cfg.sizeof_bts)
+		return -EOPNOTSUPP;
+
+	if (ds_get_bts_size(ds) <= 0)
+		return -ENXIO;
+
+	bts = get_bts_index(ds);
+
+	memset(bts, 0, ds_cfg.sizeof_bts);
+	switch (in->qualifier) {
+	case BTS_INVALID:
+		break;
+
+	case BTS_BRANCH:
+		set_from_ip(bts, in->variant.lbr.from_ip);
+		set_to_ip(bts, in->variant.lbr.to_ip);
+		break;
+
+	case BTS_TASK_ARRIVES:
+	case BTS_TASK_DEPARTS:
+		set_from_ip(bts, BTS_ESCAPE_ADDRESS);
+		set_info_type(bts, in->qualifier);
+		set_info_data(bts, in->variant.timestamp);
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	bts = (char *)bts + ds_cfg.sizeof_bts;
+	if (bts >= get_bts_absolute_maximum(ds))
+		bts = get_bts_buffer_base(ds);
+	set_bts_index(ds, bts);
+
+	return 0;
+}
+
+unsigned long ds_debugctl_mask(void)
+{
+	return ds_cfg.debugctl_mask;
+}
+
+#ifdef __i386__
+static const struct ds_configuration ds_cfg_netburst = {
+	.sizeof_ds = 9 * 4,
+	.bts_buffer_base = { 0, 4 },
+	.bts_index = { 4, 4 },
+	.bts_absolute_maximum = { 8, 4 },
+	.bts_interrupt_threshold = { 12, 4 },
+	.sizeof_bts = 3 * 4,
+	.from_ip = { 0, 4 },
+	.to_ip = { 4, 4 },
+	.info_type = { 4, 1 },
+	.info_data = { 5, 7 },
+	.debugctl_mask = (1<<2)|(1<<3)
+};
+
+static const struct ds_configuration ds_cfg_pentium_m = {
+	.sizeof_ds = 9 * 4,
+	.bts_buffer_base = { 0, 4 },
+	.bts_index = { 4, 4 },
+	.bts_absolute_maximum = { 8, 4 },
+	.bts_interrupt_threshold = { 12, 4 },
+	.sizeof_bts = 3 * 4,
+	.from_ip = { 0, 4 },
+	.to_ip = { 4, 4 },
+	.info_type = { 4, 1 },
+	.info_data = { 5, 7 },
+	.debugctl_mask = (1<<6)|(1<<7)
+};
+#endif /* _i386_ */
+
+static const struct ds_configuration ds_cfg_core2 = {
+	.sizeof_ds = 9 * 8,
+	.bts_buffer_base = { 0, 8 },
+	.bts_index = { 8, 8 },
+	.bts_absolute_maximum = { 16, 8 },
+	.bts_interrupt_threshold = { 24, 8 },
+	.sizeof_bts = 3 * 8,
+	.from_ip = { 0, 8 },
+	.to_ip = { 8, 8 },
+	.info_type = { 8, 1 },
+	.info_data = { 9, 7 },
+	.debugctl_mask = (1<<6)|(1<<7)|(1<<9)
+};
+
+static inline void
+ds_configure(const struct ds_configuration *cfg)
+{
+	ds_cfg = *cfg;
+}
+
+void __cpuinit ds_init_intel(struct cpuinfo_x86 *c)
+{
+	switch (c->x86) {
+	case 0x6:
+		switch (c->x86_model) {
+#ifdef __i386__
+		case 0xD:
+		case 0xE: /* Pentium M */
+			ds_configure(&ds_cfg_pentium_m);
+			break;
+#endif /* _i386_ */
+		case 0xF: /* Core2 */
+			ds_configure(&ds_cfg_core2);
+			break;
+		default:
+			/* sorry, don't know about them */
+			break;
+		}
+		break;
+	case 0xF:
+		switch (c->x86_model) {
+#ifdef __i386__
+		case 0x0:
+		case 0x1:
+		case 0x2: /* Netburst */
+			ds_configure(&ds_cfg_netburst);
+			break;
+#endif /* _i386_ */
+		default:
+			/* sorry, don't know about them */
+			break;
+		}
+		break;
+	default:
+		/* sorry, don't know about them */
+		break;
+	}
+}

arch/x86/kernel/process_32.c

@@ -614,11 +614,21 @@ __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 		 struct tss_struct *tss)
 {
 	struct thread_struct *prev, *next;
+	unsigned long debugctl;
 
 	prev = &prev_p->thread;
 	next = &next_p->thread;
 
-	if (next->debugctlmsr != prev->debugctlmsr)
+	debugctl = prev->debugctlmsr;
+	if (next->ds_area_msr != prev->ds_area_msr) {
+		/* we clear debugctl to make sure DS
+		 * is not in use when we change it */
+		debugctl = 0;
+		wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);
+		wrmsr(MSR_IA32_DS_AREA, next->ds_area_msr, 0);
+	}
+
+	if (next->debugctlmsr != debugctl)
 		wrmsr(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr, 0);
 
 	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
@@ -642,6 +652,13 @@ __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 	}
 #endif
 
+	if (test_tsk_thread_flag(prev_p, TIF_BTS_TRACE_TS))
+		ptrace_bts_take_timestamp(prev_p, BTS_TASK_DEPARTS);
+
+	if (test_tsk_thread_flag(next_p, TIF_BTS_TRACE_TS))
+		ptrace_bts_take_timestamp(next_p, BTS_TASK_ARRIVES);
+
+
 	if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
 		/*
 		 * Disable the bitmap via an invalid offset. We still cache

arch/x86/kernel/process_64.c

@@ -568,11 +568,21 @@ static inline void __switch_to_xtra(struct task_struct *prev_p,
 				    struct tss_struct *tss)
 {
 	struct thread_struct *prev, *next;
+	unsigned long debugctl;
 
 	prev = &prev_p->thread,
 	next = &next_p->thread;
 
-	if (next->debugctlmsr != prev->debugctlmsr)
+	debugctl = prev->debugctlmsr;
+	if (next->ds_area_msr != prev->ds_area_msr) {
+		/* we clear debugctl to make sure DS
+		 * is not in use when we change it */
+		debugctl = 0;
+		wrmsrl(MSR_IA32_DEBUGCTLMSR, 0);
+		wrmsrl(MSR_IA32_DS_AREA, next->ds_area_msr);
+	}
+
+	if (next->debugctlmsr != debugctl)
 		wrmsrl(MSR_IA32_DEBUGCTLMSR, next->debugctlmsr);
 
 	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
@@ -598,6 +608,16 @@ static inline void __switch_to_xtra(struct task_struct *prev_p,
 		 */
 		memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
 	}
+
+	/*
+	 * Last branch recording recofiguration of trace hardware and
+	 * disentangling of trace data per task.
+	 */
+	if (test_tsk_thread_flag(prev_p, TIF_BTS_TRACE_TS))
+		ptrace_bts_take_timestamp(prev_p, BTS_TASK_DEPARTS);
+
+	if (test_tsk_thread_flag(next_p, TIF_BTS_TRACE_TS))
+		ptrace_bts_take_timestamp(next_p, BTS_TASK_ARRIVES);
 }
 
 /*
@@ -701,8 +721,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	/*
 	 * Now maybe reload the debug registers and handle I/O bitmaps
 	 */
-	if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
+	if (unlikely(task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT ||
-	    || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
+		     task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
 		__switch_to_xtra(prev_p, next_p, tss);
 
 	/* If the task has used fpu the last 5 timeslices, just do a full

arch/x86/kernel/ptrace.c

@@ -2,6 +2,9 @@
 /*
  * Pentium III FXSR, SSE support
  *	Gareth Hughes <gareth@valinux.com>, May 2000
+ *
+ * BTS tracing
+ *	Markus Metzger <markus.t.metzger@intel.com>, Dec 2007
  */
 
 #include <linux/kernel.h>
@@ -26,6 +29,14 @@
 #include <asm/desc.h>
 #include <asm/prctl.h>
 #include <asm/proto.h>
+#include <asm/ds.h>
+
+
+/*
+ * The maximal size of a BTS buffer per traced task in number of BTS
+ * records.
+ */
+#define PTRACE_BTS_BUFFER_MAX 4000
 
 /*
  * does not yet catch signals sent when the child dies.
@@ -455,6 +466,165 @@ static int ptrace_set_debugreg(struct task_struct *child,
 	return 0;
 }
 
+static int ptrace_bts_max_buffer_size(void)
+{
+	return PTRACE_BTS_BUFFER_MAX;
+}
+
+static int ptrace_bts_get_buffer_size(struct task_struct *child)
+{
+	if (!child->thread.ds_area_msr)
+		return -ENXIO;
+
+	return ds_get_bts_size((void *)child->thread.ds_area_msr);
+}
+
+static int ptrace_bts_get_index(struct task_struct *child)
+{
+	if (!child->thread.ds_area_msr)
+		return -ENXIO;
+
+	return ds_get_bts_index((void *)child->thread.ds_area_msr);
+}
+
+static int ptrace_bts_read_record(struct task_struct *child,
+				  long index,
+				  struct bts_struct __user *out)
+{
+	struct bts_struct ret;
+	int retval;
+
+	if (!child->thread.ds_area_msr)
+		return -ENXIO;
+
+	retval = ds_read_bts((void *)child->thread.ds_area_msr,
+			     index, &ret);
+	if (retval)
+		return retval;
+
+	if (copy_to_user(out, &ret, sizeof(ret)))
+		return -EFAULT;
+
+	return sizeof(ret);
+}
+
+static int ptrace_bts_write_record(struct task_struct *child,
+				   const struct bts_struct *in)
+{
+	int retval;
+
+	if (!child->thread.ds_area_msr)
+		return -ENXIO;
+
+	retval = ds_write_bts((void *)child->thread.ds_area_msr, in);
+	if (retval)
+		return retval;
+
+	return sizeof(*in);
+}
+
+static int ptrace_bts_config(struct task_struct *child,
+			     unsigned long options)
+{
+	unsigned long debugctl_mask = ds_debugctl_mask();
+	int retval;
+
+	retval = ptrace_bts_get_buffer_size(child);
+	if (retval < 0)
+		return retval;
+	if (retval == 0)
+		return -ENXIO;
+
+	if (options & PTRACE_BTS_O_TRACE_TASK) {
+		child->thread.debugctlmsr |= debugctl_mask;
+		set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
+	} else {
+		/* there is no way for us to check whether we 'own'
+		 * the respective bits in the DEBUGCTL MSR, we're
+		 * about to clear */
+		child->thread.debugctlmsr &= ~debugctl_mask;
+
+		if (!child->thread.debugctlmsr)
+			clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
+	}
+
+	if (options & PTRACE_BTS_O_TIMESTAMPS)
+		set_tsk_thread_flag(child, TIF_BTS_TRACE_TS);
+	else
+		clear_tsk_thread_flag(child, TIF_BTS_TRACE_TS);
+
+	return 0;
+}
+
+static int ptrace_bts_status(struct task_struct *child)
+{
+	unsigned long debugctl_mask = ds_debugctl_mask();
+	int retval, status = 0;
+
+	retval = ptrace_bts_get_buffer_size(child);
+	if (retval < 0)
+		return retval;
+	if (retval == 0)
+		return -ENXIO;
+
+	if (ptrace_bts_get_buffer_size(child) <= 0)
+		return -ENXIO;
+
+	if (test_tsk_thread_flag(child, TIF_DEBUGCTLMSR) &&
+	    child->thread.debugctlmsr & debugctl_mask)
+		status |= PTRACE_BTS_O_TRACE_TASK;
+	if (test_tsk_thread_flag(child, TIF_BTS_TRACE_TS))
+		status |= PTRACE_BTS_O_TIMESTAMPS;
+
+	return status;
+}
+
+static int ptrace_bts_allocate_bts(struct task_struct *child,
+				   int size_in_records)
+{
+	int retval = 0;
+	void *ds;
+
+	if (size_in_records < 0)
+		return -EINVAL;
+
+	if (size_in_records > ptrace_bts_max_buffer_size())
+		return -EINVAL;
+
+	if (size_in_records == 0) {
+		ptrace_bts_config(child, /* options = */ 0);
+	} else {
+		retval = ds_allocate(&ds, size_in_records);
+		if (retval)
+			return retval;
+	}
+
+	if (child->thread.ds_area_msr)
+		ds_free((void **)&child->thread.ds_area_msr);
+
+	child->thread.ds_area_msr = (unsigned long)ds;
+	if (child->thread.ds_area_msr)
+		set_tsk_thread_flag(child, TIF_DS_AREA_MSR);
+	else
+		clear_tsk_thread_flag(child, TIF_DS_AREA_MSR);
+
+	return retval;
+}
+
+void ptrace_bts_take_timestamp(struct task_struct *tsk,
+			       enum bts_qualifier qualifier)
+{
+	struct bts_struct rec = {
+		.qualifier = qualifier,
+		.variant.timestamp = sched_clock()
+	};
+
+	if (ptrace_bts_get_buffer_size(tsk) <= 0)
+		return;
+
+	ptrace_bts_write_record(tsk, &rec);
+}
+
 /*
  * Called by kernel/ptrace.c when detaching..
  *
@@ -466,6 +636,11 @@ void ptrace_disable(struct task_struct *child)
 #ifdef TIF_SYSCALL_EMU
 	clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 #endif
+	ptrace_bts_config(child, /* options = */ 0);
+	if (child->thread.ds_area_msr) {
+	    ds_free((void **)&child->thread.ds_area_msr);
+	    clear_tsk_thread_flag(child, TIF_DS_AREA_MSR);
+	}
 }
 
 long arch_ptrace(struct task_struct *child, long request, long addr, long data)
@@ -626,6 +801,36 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data)
 		break;
 #endif
 
+	case PTRACE_BTS_MAX_BUFFER_SIZE:
+		ret = ptrace_bts_max_buffer_size();
+		break;
+
+	case PTRACE_BTS_ALLOCATE_BUFFER:
+		ret = ptrace_bts_allocate_bts(child, data);
+		break;
+
+	case PTRACE_BTS_GET_BUFFER_SIZE:
+		ret = ptrace_bts_get_buffer_size(child);
+		break;
+
+	case PTRACE_BTS_GET_INDEX:
+		ret = ptrace_bts_get_index(child);
+		break;
+
+	case PTRACE_BTS_READ_RECORD:
+		ret = ptrace_bts_read_record
+			(child, data,
+			 (struct bts_struct __user *) addr);
+		break;
+
+	case PTRACE_BTS_CONFIG:
+		ret = ptrace_bts_config(child, data);
+		break;
+
+	case PTRACE_BTS_STATUS:
+		ret = ptrace_bts_status(child);
+		break;
+
 	default:
 		ret = ptrace_request(child, request, addr, data);
 		break;
@@ -809,6 +1014,13 @@ asmlinkage long sys32_ptrace(long request, u32 pid, u32 addr, u32 data)
 	case PTRACE_SETOPTIONS:
 	case PTRACE_SET_THREAD_AREA:
 	case PTRACE_GET_THREAD_AREA:
+	case PTRACE_BTS_MAX_BUFFER_SIZE:
+	case PTRACE_BTS_ALLOCATE_BUFFER:
+	case PTRACE_BTS_GET_BUFFER_SIZE:
+	case PTRACE_BTS_GET_INDEX:
+	case PTRACE_BTS_READ_RECORD:
+	case PTRACE_BTS_CONFIG:
+	case PTRACE_BTS_STATUS:
 		return sys_ptrace(request, pid, addr, data);
 
 	default:

arch/x86/kernel/setup_64.c

@@ -60,6 +60,7 @@
 #include <asm/dmi.h>
 #include <asm/cacheflush.h>
 #include <asm/mce.h>
+#include <asm/ds.h>
 
 /*
  * Machine setup..
@@ -823,6 +824,10 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
 			set_cpu_cap(c, X86_FEATURE_PEBS);
 	}
 
+
+	if (cpu_has_bts)
+		ds_init_intel(c);
+
 	n = c->extended_cpuid_level;
 	if (n >= 0x80000008) {
 		unsigned eax = cpuid_eax(0x80000008);

arch/x86/kernel/step.c

@@ -169,9 +169,14 @@ static void enable_step(struct task_struct *child, bool block)
 	 */
 	if (enable_single_step(child) && block) {
 		set_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
-		write_debugctlmsr(child, DEBUGCTLMSR_BTF);
+		write_debugctlmsr(child,
-	} else if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR)) {
+				  child->thread.debugctlmsr | DEBUGCTLMSR_BTF);
-		write_debugctlmsr(child, 0);
+	} else {
+	    write_debugctlmsr(child,
+			      child->thread.debugctlmsr & ~TIF_DEBUGCTLMSR);
+
+	    if (!child->thread.debugctlmsr)
+		    clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
 	}
 }
 
@@ -190,8 +195,11 @@ void user_disable_single_step(struct task_struct *child)
 	/*
 	 * Make sure block stepping (BTF) is disabled.
 	 */
-	if (test_and_clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR))
+	write_debugctlmsr(child,
-		write_debugctlmsr(child, 0);
+			  child->thread.debugctlmsr & ~TIF_DEBUGCTLMSR);
+
+	if (!child->thread.debugctlmsr)
+		clear_tsk_thread_flag(child, TIF_DEBUGCTLMSR);
 
 	/* Always clear TIF_SINGLESTEP... */
 	clear_tsk_thread_flag(child, TIF_SINGLESTEP);

include/asm-x86/ds.h

@@ -0,0 +1,65 @@
+/*
+ * Debug Store (DS) support
+ *
+ * This provides a low-level interface to the hardware's Debug Store
+ * feature that is used for last branch recording (LBR) and
+ * precise-event based sampling (PEBS).
+ *
+ * Different architectures use a different DS layout/pointer size.
+ * The below functions therefore work on a void*.
+ *
+ *
+ * Since there is no user for PEBS, yet, only LBR (or branch
+ * trace store, BTS) is supported.
+ *
+ *
+ * Copyright (C) 2007 Intel Corporation.
+ * Markus Metzger <markus.t.metzger@intel.com>, Dec 2007
+ */
+
+#ifndef _ASM_X86_DS_H
+#define _ASM_X86_DS_H
+
+#include <linux/types.h>
+#include <linux/init.h>
+
+struct cpuinfo_x86;
+
+
+/* a branch trace record entry
+ *
+ * In order to unify the interface between various processor versions,
+ * we use the below data structure for all processors.
+ */
+enum bts_qualifier {
+	BTS_INVALID = 0,
+	BTS_BRANCH,
+	BTS_TASK_ARRIVES,
+	BTS_TASK_DEPARTS
+};
+
+struct bts_struct {
+	enum bts_qualifier qualifier;
+	union {
+		/* BTS_BRANCH */
+		struct {
+			long from_ip;
+			long to_ip;
+		} lbr;
+		/* BTS_TASK_ARRIVES or
+		   BTS_TASK_DEPARTS */
+		unsigned long long timestamp;
+	} variant;
+};
+
+
+extern int ds_allocate(void **, size_t);
+extern int ds_free(void **);
+extern int ds_get_bts_size(void *);
+extern int ds_get_bts_index(void *);
+extern int ds_read_bts(void *, size_t, struct bts_struct *);
+extern int ds_write_bts(void *, const struct bts_struct *);
+extern unsigned long ds_debugctl_mask(void);
+extern void __cpuinit ds_init_intel(struct cpuinfo_x86 *c);
+
+#endif /* _ASM_X86_DS_H */

include/asm-x86/processor_32.h

@@ -360,6 +360,9 @@ struct thread_struct {
 	unsigned long	io_bitmap_max;
 /* MSR_IA32_DEBUGCTLMSR value to switch in if TIF_DEBUGCTLMSR is set.  */
 	unsigned long	debugctlmsr;
+/* Debug Store - if not 0 points to a DS Save Area configuration;
+ *               goes into MSR_IA32_DS_AREA */
+	unsigned long	ds_area_msr;
 };
 
 #define INIT_THREAD  {							\

include/asm-x86/processor_64.h

@@ -240,6 +240,9 @@ struct thread_struct {
 	unsigned io_bitmap_max;
 /* MSR_IA32_DEBUGCTLMSR value to switch in if TIF_DEBUGCTLMSR is set.  */
 	unsigned long	debugctlmsr;
+/* Debug Store - if not 0 points to a DS Save Area configuration;
+ *               goes into MSR_IA32_DS_AREA */
+	unsigned long	ds_area_msr;
 /* cached TLS descriptors. */
 	u64 tls_array[GDT_ENTRY_TLS_ENTRIES];
 } __attribute__((aligned(16)));

include/asm-x86/ptrace-abi.h

@@ -80,4 +80,56 @@
 
 #define PTRACE_SINGLEBLOCK	33	/* resume execution until next branch */
 
+/* Return maximal BTS buffer size in number of records,
+   if successuf; -1, otherwise.
+   EOPNOTSUPP...processor does not support bts tracing */
+#define PTRACE_BTS_MAX_BUFFER_SIZE 40
+
+/* Allocate new bts buffer (free old one, if exists) of size DATA bts records;
+   parameter ADDR is ignored.
+   Return 0, if successful; -1, otherwise.
+   EOPNOTSUPP...processor does not support bts tracing
+   EINVAL.......invalid size in records
+   ENOMEM.......out of memory */
+#define PTRACE_BTS_ALLOCATE_BUFFER 41
+
+/* Return the size of the bts buffer in number of bts records,
+   if successful; -1, otherwise.
+   EOPNOTSUPP...processor does not support bts tracing
+   ENXIO........no buffer allocated */
+#define PTRACE_BTS_GET_BUFFER_SIZE 42
+
+/* Return the index of the next bts record to be written,
+   if successful; -1, otherwise.
+   EOPNOTSUPP...processor does not support bts tracing
+   ENXIO........no buffer allocated
+   After the first warp-around, this is the start of the circular bts buffer. */
+#define PTRACE_BTS_GET_INDEX 43
+
+/* Read the DATA'th bts record into a ptrace_bts_record buffer provided in ADDR.
+   Return 0, if successful; -1, otherwise
+   EOPNOTSUPP...processor does not support bts tracing
+   ENXIO........no buffer allocated
+   EINVAL.......invalid index */
+#define PTRACE_BTS_READ_RECORD 44
+
+/* Configure last branch trace; the configuration is given as a bit-mask of
+   PTRACE_BTS_O_* options in DATA; parameter ADDR is ignored.
+   Return 0, if successful; -1, otherwise
+   EOPNOTSUPP...processor does not support bts tracing
+   ENXIO........no buffer allocated */
+#define PTRACE_BTS_CONFIG 45
+
+/* Return the configuration as bit-mask of PTRACE_BTS_O_* options
+   if successful; -1, otherwise.
+   EOPNOTSUPP...processor does not support bts tracing
+   ENXIO........no buffer allocated */
+#define PTRACE_BTS_STATUS 46
+
+/* Trace configuration options */
+/* Collect last branch trace */
+#define PTRACE_BTS_O_TRACE_TASK 0x1
+/* Take timestamps when the task arrives and departs */
+#define PTRACE_BTS_O_TIMESTAMPS 0x2
+
 #endif

include/asm-x86/ptrace.h

@@ -4,8 +4,19 @@
 #include <linux/compiler.h>	/* For __user */
 #include <asm/ptrace-abi.h>
 
+
 #ifndef __ASSEMBLY__
 
+#ifdef __KERNEL__
+
+#include <asm/ds.h>
+
+struct task_struct;
+extern void ptrace_bts_take_timestamp(struct task_struct *, enum bts_qualifier);
+
+#endif /* __KERNEL__ */
+
+
 #ifdef __i386__
 /* this struct defines the way the registers are stored on the
    stack during a system call. */

include/asm-x86/thread_info_32.h

@@ -140,6 +140,8 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_NOTSC		20	/* TSC is not accessible in userland */
 #define TIF_FORCED_TF		21	/* true if TF in eflags artificially */
 #define TIF_DEBUGCTLMSR		22	/* uses thread_struct.debugctlmsr */
+#define TIF_DS_AREA_MSR 	23      /* uses thread_struct.ds_area_msr */
+#define TIF_BTS_TRACE_TS        24      /* record scheduling event timestamps */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
@@ -157,6 +159,8 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_NOTSC		(1<<TIF_NOTSC)
 #define _TIF_FORCED_TF		(1<<TIF_FORCED_TF)
 #define _TIF_DEBUGCTLMSR	(1<<TIF_DEBUGCTLMSR)
+#define _TIF_DS_AREA_MSR	(1<<TIF_DS_AREA_MSR)
+#define _TIF_BTS_TRACE_TS	(1<<TIF_BTS_TRACE_TS)
 
 /* work to do on interrupt/exception return */
 #define _TIF_WORK_MASK \
@@ -166,8 +170,12 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_ALLWORK_MASK	(0x0000FFFF & ~_TIF_SECCOMP)
 
 /* flags to check in __switch_to() */
-#define _TIF_WORK_CTXSW_NEXT (_TIF_IO_BITMAP | _TIF_NOTSC | _TIF_DEBUG | _TIF_DEBUGCTLMSR)
+#define _TIF_WORK_CTXSW \
-#define _TIF_WORK_CTXSW_PREV (_TIF_IO_BITMAP | _TIF_NOTSC | _TIF_DEBUGCTLMSR)
+    (_TIF_IO_BITMAP | _TIF_NOTSC | _TIF_DEBUGCTLMSR | \
+     _TIF_DS_AREA_MSR | _TIF_BTS_TRACE_TS)
+#define _TIF_WORK_CTXSW_PREV _TIF_WORK_CTXSW
+#define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW | _TIF_DEBUG)
+
 
 /*
  * Thread-synchronous status.

include/asm-x86/thread_info_64.h

@@ -123,6 +123,8 @@ static inline struct thread_info *stack_thread_info(void)
 #define TIF_FREEZE		23	/* is freezing for suspend */
 #define TIF_FORCED_TF		24	/* true if TF in eflags artificially */
 #define TIF_DEBUGCTLMSR		25	/* uses thread_struct.debugctlmsr */
+#define TIF_DS_AREA_MSR	25      /* uses thread_struct.ds_area_msr */
+#define TIF_BTS_TRACE_TS	26      /* record scheduling event timestamps */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
@@ -142,6 +144,8 @@ static inline struct thread_info *stack_thread_info(void)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)
 #define _TIF_FORCED_TF		(1<<TIF_FORCED_TF)
 #define _TIF_DEBUGCTLMSR	(1<<TIF_DEBUGCTLMSR)
+#define _TIF_DS_AREA_MSR	(1<<TIF_DS_AREA_MSR)
+#define _TIF_BTS_TRACE_TS	(1<<TIF_BTS_TRACE_TS)
 
 /* work to do on interrupt/exception return */
 #define _TIF_WORK_MASK \
@@ -153,7 +157,10 @@ static inline struct thread_info *stack_thread_info(void)
 	(_TIF_SIGPENDING|_TIF_SINGLESTEP|_TIF_MCE_NOTIFY|_TIF_HRTICK_RESCHED)
 
 /* flags to check in __switch_to() */
-#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP|_TIF_DEBUGCTLMSR)
+#define _TIF_WORK_CTXSW \
+    (_TIF_IO_BITMAP|_TIF_DEBUGCTLMSR|_TIF_DS_AREA_MSR|_TIF_BTS_TRACE_TS)
+#define _TIF_WORK_CTXSW_PREV _TIF_WORK_CTXSW
+#define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW|_TIF_DEBUG)
 
 #define PREEMPT_ACTIVE     0x10000000