x86, bts: provide in-kernel branch-trace interface

Impact: cleanup

Move the BTS bits from ptrace.c into ds.c.

Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 528 insertions, 329 deletions

diff --git a/arch/x86/kernel/ds.c b/arch/x86/kernel/ds.c
index 095306988667..f0583005b75e 100644
--- a/arch/x86/kernel/ds.c
+++ b/arch/x86/kernel/ds.c
@@ -6,13 +6,13 @@
  * precise-event based sampling (PEBS).
  *
  * It manages:
- * - per-thread and per-cpu allocation of BTS and PEBS
+ * - DS and BTS hardware configuration
  * - buffer overflow handling (to be done)
  * - buffer access
  *
- * It assumes:
- * - get_task_struct on all traced tasks
- * - current is allowed to trace tasks
+ * It does not do:
+ * - security checking (is the caller allowed to trace the task)
+ * - buffer allocation (memory accounting)
  *
  *
  * Copyright (C) 2007-2008 Intel Corporation.
@@ -34,15 +34,30 @@
  * The configuration for a particular DS hardware implementation.
  */
 struct ds_configuration {
-	/* the size of the DS structure in bytes */
-	unsigned char  sizeof_ds;
-	/* the size of one pointer-typed field in the DS structure in bytes;
-	   this covers the first 8 fields related to buffer management. */
+	/* the name of the configuration */
+	const char *name;
+	/* the size of one pointer-typed field in the DS structure and
+	   in the BTS and PEBS buffers in bytes;
+	   this covers the first 8 DS fields related to buffer management. */
 	unsigned char  sizeof_field;
 	/* the size of a BTS/PEBS record in bytes */
 	unsigned char  sizeof_rec[2];
+	/* a series of bit-masks to control various features indexed
+	 * by enum ds_feature */
+	unsigned long ctl[dsf_ctl_max];
 };
-static struct ds_configuration ds_cfg;
+static DEFINE_PER_CPU(struct ds_configuration, ds_cfg_array);
+
+#define ds_cfg per_cpu(ds_cfg_array, smp_processor_id())
+
+#define MAX_SIZEOF_DS (12 * 8)	/* maximal size of a DS configuration */
+#define MAX_SIZEOF_BTS (3 * 8)	/* maximal size of a BTS record */
+#define DS_ALIGNMENT (1 << 3)	/* BTS and PEBS buffer alignment */
+
+#define BTS_CONTROL \
+ (ds_cfg.ctl[dsf_bts] | ds_cfg.ctl[dsf_bts_kernel] | ds_cfg.ctl[dsf_bts_user] |\
+  ds_cfg.ctl[dsf_bts_overflow])
+
 
 /*
  * A BTS or PEBS tracer.
@@ -61,6 +76,8 @@ struct ds_tracer {
 struct bts_tracer {
 	/* the common DS part */
 	struct ds_tracer ds;
+	/* the trace including the DS configuration */
+	struct bts_trace trace;
 	/* buffer overflow notification function */
 	bts_ovfl_callback_t ovfl;
 };
@@ -68,6 +85,8 @@ struct bts_tracer {
 struct pebs_tracer {
 	/* the common DS part */
 	struct ds_tracer ds;
+	/* the trace including the DS configuration */
+	struct pebs_trace trace;
 	/* buffer overflow notification function */
 	pebs_ovfl_callback_t ovfl;
 };
@@ -134,13 +153,11 @@ static inline void ds_set(unsigned char *base, enum ds_qualifier qual,
 	(*(unsigned long *)base) = value;
 }
 
-#define DS_ALIGNMENT (1 << 3)	/* BTS and PEBS buffer alignment */
-
 
 /*
  * Locking is done only for allocating BTS or PEBS resources.
  */
-static spinlock_t ds_lock = __SPIN_LOCK_UNLOCKED(ds_lock);
+static DEFINE_SPINLOCK(ds_lock);
 
 
 /*
@@ -156,27 +173,32 @@ static spinlock_t ds_lock = __SPIN_LOCK_UNLOCKED(ds_lock);
  *   >0  number of per-thread tracers
  *   <0  number of per-cpu tracers
  *
- * The below functions to get and put tracers and to check the
- * allocation type require the ds_lock to be held by the caller.
- *
  * Tracers essentially gives the number of ds contexts for a certain
  * type of allocation.
  */
-static long tracers;
+static atomic_t tracers = ATOMIC_INIT(0);
 
 static inline void get_tracer(struct task_struct *task)
 {
-	tracers += (task ? 1 : -1);
+	if (task)
+		atomic_inc(&tracers);
+	else
+		atomic_dec(&tracers);
 }
 
 static inline void put_tracer(struct task_struct *task)
 {
-	tracers -= (task ? 1 : -1);
+	if (task)
+		atomic_dec(&tracers);
+	else
+		atomic_inc(&tracers);
 }
 
 static inline int check_tracer(struct task_struct *task)
 {
-	return (task ? (tracers >= 0) : (tracers <= 0));
+	return task ?
+		(atomic_read(&tracers) >= 0) :
+		(atomic_read(&tracers) <= 0);
 }
 
 
@@ -190,14 +212,30 @@ static inline int check_tracer(struct task_struct *task)
  * Contexts are use-counted. They are allocated on first access and
  * deallocated when the last user puts the context.
  */
-static DEFINE_PER_CPU(struct ds_context *, system_context);
+struct ds_context {
+	/* pointer to the DS configuration; goes into MSR_IA32_DS_AREA */
+	unsigned char ds[MAX_SIZEOF_DS];
+	/* the owner of the BTS and PEBS configuration, respectively */
+	struct bts_tracer *bts_master;
+	struct pebs_tracer *pebs_master;
+	/* use count */
+	unsigned long count;
+	/* a pointer to the context location inside the thread_struct
+	 * or the per_cpu context array */
+	struct ds_context **this;
+	/* a pointer to the task owning this context, or NULL, if the
+	 * context is owned by a cpu */
+	struct task_struct *task;
+};
+
+static DEFINE_PER_CPU(struct ds_context *, system_context_array);
 
-#define this_system_context per_cpu(system_context, smp_processor_id())
+#define system_context per_cpu(system_context_array, smp_processor_id())
 
 static inline struct ds_context *ds_get_context(struct task_struct *task)
 {
 	struct ds_context **p_context =
-		(task ? &task->thread.ds_ctx : &this_system_context);
+		(task ? &task->thread.ds_ctx : &system_context);
 	struct ds_context *context = *p_context;
 	unsigned long irq;
 
@@ -225,10 +263,22 @@ static inline struct ds_context *ds_get_context(struct task_struct *task)
 				wrmsrl(MSR_IA32_DS_AREA,
 				       (unsigned long)context->ds);
 		}
+
+		context->count++;
+
+		spin_unlock_irqrestore(&ds_lock, irq);
+	} else {
+		spin_lock_irqsave(&ds_lock, irq);
+
+		context = *p_context;
+		if (context)
+			context->count++;
+
 		spin_unlock_irqrestore(&ds_lock, irq);
-	}
 
-	context->count++;
+		if (!context)
+			context = ds_get_context(task);
+	}
 
 	return context;
 }
@@ -242,8 +292,10 @@ static inline void ds_put_context(struct ds_context *context)
 
 	spin_lock_irqsave(&ds_lock, irq);
 
-	if (--context->count)
-		goto out;
+	if (--context->count) {
+		spin_unlock_irqrestore(&ds_lock, irq);
+		return;
+	}
 
 	*(context->this) = NULL;
 
@@ -253,14 +305,14 @@ static inline void ds_put_context(struct ds_context *context)
 	if (!context->task || (context->task == current))
 		wrmsrl(MSR_IA32_DS_AREA, 0);
 
-	kfree(context);
- out:
 	spin_unlock_irqrestore(&ds_lock, irq);
+
+	kfree(context);
 }
 
 
 /*
- * Handle a buffer overflow
+ * Call the tracer's callback on a buffer overflow.
  *
  * context: the ds context
  * qual: the buffer type
@@ -268,30 +320,244 @@ static inline void ds_put_context(struct ds_context *context)
 static void ds_overflow(struct ds_context *context, enum ds_qualifier qual)
 {
 	switch (qual) {
-	case ds_bts: {
-		struct bts_tracer *tracer =
-			container_of(context->owner[qual],
-				     struct bts_tracer, ds);
-		if (tracer->ovfl)
-			tracer->ovfl(tracer);
-	}
+	case ds_bts:
+		if (context->bts_master &&
+		    context->bts_master->ovfl)
+			context->bts_master->ovfl(context->bts_master);
+		break;
+	case ds_pebs:
+		if (context->pebs_master &&
+		    context->pebs_master->ovfl)
+			context->pebs_master->ovfl(context->pebs_master);
 		break;
-	case ds_pebs: {
-		struct pebs_tracer *tracer =
-			container_of(context->owner[qual],
-				     struct pebs_tracer, ds);
-		if (tracer->ovfl)
-			tracer->ovfl(tracer);
 	}
+}
+
+
+/*
+ * Write raw data into the BTS or PEBS buffer.
+ *
+ * The remainder of any partially written record is zeroed out.
+ *
+ * context: the DS context
+ * qual: the buffer type
+ * record: the data to write
+ * size: the size of the data
+ */
+static int ds_write(struct ds_context *context, enum ds_qualifier qual,
+		    const void *record, size_t size)
+{
+	int bytes_written = 0;
+
+	if (!record)
+		return -EINVAL;
+
+	while (size) {
+		unsigned long base, index, end, write_end, int_th;
+		unsigned long write_size, adj_write_size;
+
+		/*
+		 * write as much as possible without producing an
+		 * overflow interrupt.
+		 *
+		 * interrupt_threshold must either be
+		 * - bigger than absolute_maximum or
+		 * - point to a record between buffer_base and absolute_maximum
+		 *
+		 * index points to a valid record.
+		 */
+		base   = ds_get(context->ds, qual, ds_buffer_base);
+		index  = ds_get(context->ds, qual, ds_index);
+		end    = ds_get(context->ds, qual, ds_absolute_maximum);
+		int_th = ds_get(context->ds, qual, ds_interrupt_threshold);
+
+		write_end = min(end, int_th);
+
+		/* if we are already beyond the interrupt threshold,
+		 * we fill the entire buffer */
+		if (write_end <= index)
+			write_end = end;
+
+		if (write_end <= index)
+			break;
+
+		write_size = min((unsigned long) size, write_end - index);
+		memcpy((void *)index, record, write_size);
+
+		record = (const char *)record + write_size;
+		size -= write_size;
+		bytes_written += write_size;
+
+		adj_write_size = write_size / ds_cfg.sizeof_rec[qual];
+		adj_write_size *= ds_cfg.sizeof_rec[qual];
+
+		/* zero out trailing bytes */
+		memset((char *)index + write_size, 0,
+		       adj_write_size - write_size);
+		index += adj_write_size;
+
+		if (index >= end)
+			index = base;
+		ds_set(context->ds, qual, ds_index, index);
+
+		if (index >= int_th)
+			ds_overflow(context, qual);
+	}
+
+	return bytes_written;
+}
+
+
+/*
+ * Branch Trace Store (BTS) uses the following format. Different
+ * architectures vary in the size of those fields.
+ * - source linear address
+ * - destination linear address
+ * - flags
+ *
+ * Later architectures use 64bit pointers throughout, whereas earlier
+ * architectures use 32bit pointers in 32bit mode.
+ *
+ * We compute the base address for the first 8 fields based on:
+ * - the field size stored in the DS configuration
+ * - the relative field position
+ *
+ * In order to store additional information in the BTS buffer, we use
+ * a special source address to indicate that the record requires
+ * special interpretation.
+ *
+ * Netburst indicated via a bit in the flags field whether the branch
+ * was predicted; this is ignored.
+ *
+ * We use two levels of abstraction:
+ * - the raw data level defined here
+ * - an arch-independent level defined in ds.h
+ */
+
+enum bts_field {
+	bts_from,
+	bts_to,
+	bts_flags,
+
+	bts_qual = bts_from,
+	bts_jiffies = bts_to,
+	bts_pid = bts_flags,
+
+	bts_qual_mask = (bts_qual_max - 1),
+	bts_escape = ((unsigned long)-1 & ~bts_qual_mask)
+};
+
+static inline unsigned long bts_get(const char *base, enum bts_field field)
+{
+	base += (ds_cfg.sizeof_field * field);
+	return *(unsigned long *)base;
+}
+
+static inline void bts_set(char *base, enum bts_field field, unsigned long val)
+{
+	base += (ds_cfg.sizeof_field * field);;
+	(*(unsigned long *)base) = val;
+}
+
+
+/*
+ * The raw BTS data is architecture dependent.
+ *
+ * For higher-level users, we give an arch-independent view.
+ * - ds.h defines struct bts_struct
+ * - bts_read translates one raw bts record into a bts_struct
+ * - bts_write translates one bts_struct into the raw format and
+ *   writes it into the top of the parameter tracer's buffer.
+ *
+ * return: bytes read/written on success; -Eerrno, otherwise
+ */
+static int bts_read(struct bts_tracer *tracer, const void *at,
+		    struct bts_struct *out)
+{
+	if (!tracer)
+		return -EINVAL;
+
+	if (at < tracer->trace.ds.begin)
+		return -EINVAL;
+
+	if (tracer->trace.ds.end < (at + tracer->trace.ds.size))
+		return -EINVAL;
+
+	memset(out, 0, sizeof(*out));
+	if ((bts_get(at, bts_qual) & ~bts_qual_mask) == bts_escape) {
+		out->qualifier = (bts_get(at, bts_qual) & bts_qual_mask);
+		out->variant.timestamp.jiffies = bts_get(at, bts_jiffies);
+		out->variant.timestamp.pid = bts_get(at, bts_pid);
+	} else {
+		out->qualifier = bts_branch;
+		out->variant.lbr.from = bts_get(at, bts_from);
+		out->variant.lbr.to   = bts_get(at, bts_to);
+	}
+
+	return ds_cfg.sizeof_rec[ds_bts];
+}
+
+static int bts_write(struct bts_tracer *tracer, const struct bts_struct *in)
+{
+	unsigned char raw[MAX_SIZEOF_BTS];
+
+	if (!tracer)
+		return -EINVAL;
+
+	if (MAX_SIZEOF_BTS < ds_cfg.sizeof_rec[ds_bts])
+		return -EOVERFLOW;
+
+	switch (in->qualifier) {
+	case bts_invalid:
+		bts_set(raw, bts_from, 0);
+		bts_set(raw, bts_to, 0);
+		bts_set(raw, bts_flags, 0);
+		break;
+	case bts_branch:
+		bts_set(raw, bts_from, in->variant.lbr.from);
+		bts_set(raw, bts_to,   in->variant.lbr.to);
+		bts_set(raw, bts_flags, 0);
+		break;
+	case bts_task_arrives:
+	case bts_task_departs:
+		bts_set(raw, bts_qual, (bts_escape | in->qualifier));
+		bts_set(raw, bts_jiffies, in->variant.timestamp.jiffies);
+		bts_set(raw, bts_pid, in->variant.timestamp.pid);
 		break;
+	default:
+		return -EINVAL;
 	}
+
+	return ds_write(tracer->ds.context, ds_bts, raw,
+			ds_cfg.sizeof_rec[ds_bts]);
 }
 
 
-static void ds_install_ds_config(struct ds_context *context,
-				 enum ds_qualifier qual,
-				 void *base, size_t size, size_t ith)
+static void ds_write_config(struct ds_context *context,
+			    struct ds_trace *cfg, enum ds_qualifier qual)
+{
+	unsigned char *ds = context->ds;
+
+	ds_set(ds, qual, ds_buffer_base, (unsigned long)cfg->begin);
+	ds_set(ds, qual, ds_index, (unsigned long)cfg->top);
+	ds_set(ds, qual, ds_absolute_maximum, (unsigned long)cfg->end);
+	ds_set(ds, qual, ds_interrupt_threshold, (unsigned long)cfg->ith);
+}
+
+static void ds_read_config(struct ds_context *context,
+			   struct ds_trace *cfg, enum ds_qualifier qual)
 {
+	unsigned char *ds = context->ds;
+
+	cfg->begin = (void *)ds_get(ds, qual, ds_buffer_base);
+	cfg->top = (void *)ds_get(ds, qual, ds_index);
+	cfg->end = (void *)ds_get(ds, qual, ds_absolute_maximum);
+	cfg->ith = (void *)ds_get(ds, qual, ds_interrupt_threshold);
+}
+
+static void ds_init_ds_trace(struct ds_trace *trace, enum ds_qualifier qual,
+			     void *base, size_t size, size_t ith,
+			     unsigned int flags) {
 	unsigned long buffer, adj;
 
 	/* adjust the buffer address and size to meet alignment
@@ -308,32 +574,30 @@ static void ds_install_ds_config(struct ds_context *context,
 	buffer += adj;
 	size   -= adj;
 
-	size /= ds_cfg.sizeof_rec[qual];
-	size *= ds_cfg.sizeof_rec[qual];
+	trace->n = size / ds_cfg.sizeof_rec[qual];
+	trace->size = ds_cfg.sizeof_rec[qual];
 
-	ds_set(context->ds, qual, ds_buffer_base, buffer);
-	ds_set(context->ds, qual, ds_index, buffer);
-	ds_set(context->ds, qual, ds_absolute_maximum, buffer + size);
+	size = (trace->n * trace->size);
 
+	trace->begin = (void *)buffer;
+	trace->top = trace->begin;
+	trace->end = (void *)(buffer + size);
 	/* The value for 'no threshold' is -1, which will set the
 	 * threshold outside of the buffer, just like we want it.
 	 */
-	ds_set(context->ds, qual,
-	       ds_interrupt_threshold, buffer + size - ith);
+	trace->ith = (void *)(buffer + size - ith);
+
+	trace->flags = flags;
 }
 
-static int ds_request(struct ds_tracer *tracer, enum ds_qualifier qual,
-		      struct task_struct *task,
-		      void *base, size_t size, size_t th)
+
+static int ds_request(struct ds_tracer *tracer, struct ds_trace *trace,
+		      enum ds_qualifier qual, struct task_struct *task,
+		      void *base, size_t size, size_t th, unsigned int flags)
 {
 	struct ds_context *context;
-	unsigned long irq;
 	int error;
 
-	error = -EOPNOTSUPP;
-	if (!ds_cfg.sizeof_ds)
-		goto out;
-
 	error = -EINVAL;
 	if (!base)
 		goto out;
@@ -360,43 +624,26 @@ static int ds_request(struct ds_tracer *tracer, enum ds_qualifier qual,
 		goto out;
 	tracer->context = context;
 
+	ds_init_ds_trace(trace, qual, base, size, th, flags);
 
-	spin_lock_irqsave(&ds_lock, irq);
-
-	error = -EPERM;
-	if (!check_tracer(task))
-		goto out_unlock;
-	get_tracer(task);
-
-	error = -EPERM;
-	if (context->owner[qual])
-		goto out_put_tracer;
-	context->owner[qual] = tracer;
-
-	spin_unlock_irqrestore(&ds_lock, irq);
-
-
-	ds_install_ds_config(context, qual, base, size, th);
-
-	return 0;
-
- out_put_tracer:
-	put_tracer(task);
- out_unlock:
-	spin_unlock_irqrestore(&ds_lock, irq);
-	ds_put_context(context);
-	tracer->context = NULL;
+	error = 0;
  out:
 	return error;
 }
 
 struct bts_tracer *ds_request_bts(struct task_struct *task,
 				  void *base, size_t size,
-				  bts_ovfl_callback_t ovfl, size_t th)
+				  bts_ovfl_callback_t ovfl, size_t th,
+				  unsigned int flags)
 {
 	struct bts_tracer *tracer;
+	unsigned long irq;
 	int error;
 
+	error = -EOPNOTSUPP;
+	if (!ds_cfg.ctl[dsf_bts])
+		goto out;
+
 	/* buffer overflow notification is not yet implemented */
 	error = -EOPNOTSUPP;
 	if (ovfl)
@@ -408,12 +655,40 @@ struct bts_tracer *ds_request_bts(struct task_struct *task,
 		goto out;
 	tracer->ovfl = ovfl;
 
-	error = ds_request(&tracer->ds, ds_bts, task, base, size, th);
+	error = ds_request(&tracer->ds, &tracer->trace.ds,
+			   ds_bts, task, base, size, th, flags);
 	if (error < 0)
 		goto out_tracer;
 
+
+	spin_lock_irqsave(&ds_lock, irq);
+
+	error = -EPERM;
+	if (!check_tracer(task))
+		goto out_unlock;
+	get_tracer(task);
+
+	error = -EPERM;
+	if (tracer->ds.context->bts_master)
+		goto out_put_tracer;
+	tracer->ds.context->bts_master = tracer;
+
+	spin_unlock_irqrestore(&ds_lock, irq);
+
+
+	tracer->trace.read  = bts_read;
+	tracer->trace.write = bts_write;
+
+	ds_write_config(tracer->ds.context, &tracer->trace.ds, ds_bts);
+	ds_resume_bts(tracer);
+
 	return tracer;
 
+ out_put_tracer:
+	put_tracer(task);
+ out_unlock:
+	spin_unlock_irqrestore(&ds_lock, irq);
+	ds_put_context(tracer->ds.context);
  out_tracer:
 	kfree(tracer);
  out:
@@ -422,9 +697,11 @@ struct bts_tracer *ds_request_bts(struct task_struct *task,
 
 struct pebs_tracer *ds_request_pebs(struct task_struct *task,
 				    void *base, size_t size,
-				    pebs_ovfl_callback_t ovfl, size_t th)
+				    pebs_ovfl_callback_t ovfl, size_t th,
+				    unsigned int flags)
 {
 	struct pebs_tracer *tracer;
+	unsigned long irq;
 	int error;
 
 	/* buffer overflow notification is not yet implemented */
@@ -438,300 +715,171 @@ struct pebs_tracer *ds_request_pebs(struct task_struct *task,
 		goto out;
 	tracer->ovfl = ovfl;
 
-	error = ds_request(&tracer->ds, ds_pebs, task, base, size, th);
+	error = ds_request(&tracer->ds, &tracer->trace.ds,
+			   ds_pebs, task, base, size, th, flags);
 	if (error < 0)
 		goto out_tracer;
 
+	spin_lock_irqsave(&ds_lock, irq);
+
+	error = -EPERM;
+	if (!check_tracer(task))
+		goto out_unlock;
+	get_tracer(task);
+
+	error = -EPERM;
+	if (tracer->ds.context->pebs_master)
+		goto out_put_tracer;
+	tracer->ds.context->pebs_master = tracer;
+
+	spin_unlock_irqrestore(&ds_lock, irq);
+
+	ds_write_config(tracer->ds.context, &tracer->trace.ds, ds_bts);
+	ds_resume_pebs(tracer);
+
 	return tracer;
 
+ out_put_tracer:
+	put_tracer(task);
+ out_unlock:
+	spin_unlock_irqrestore(&ds_lock, irq);
+	ds_put_context(tracer->ds.context);
  out_tracer:
 	kfree(tracer);
  out:
 	return ERR_PTR(error);
 }
 
-static void ds_release(struct ds_tracer *tracer, enum ds_qualifier qual)
-{
-	WARN_ON_ONCE(tracer->context->owner[qual] != tracer);
-	tracer->context->owner[qual] = NULL;
-
-	put_tracer(tracer->context->task);
-	ds_put_context(tracer->context);
-}
-
-int ds_release_bts(struct bts_tracer *tracer)
+void ds_release_bts(struct bts_tracer *tracer)
 {
 	if (!tracer)
-		return -EINVAL;
+		return;
 
-	ds_release(&tracer->ds, ds_bts);
-	kfree(tracer);
+	ds_suspend_bts(tracer);
 
-	return 0;
-}
+	WARN_ON_ONCE(tracer->ds.context->bts_master != tracer);
+	tracer->ds.context->bts_master = NULL;
 
-int ds_release_pebs(struct pebs_tracer *tracer)
-{
-	if (!tracer)
-		return -EINVAL;
+	put_tracer(tracer->ds.context->task);
+	ds_put_context(tracer->ds.context);
 
-	ds_release(&tracer->ds, ds_pebs);
 	kfree(tracer);
-
-	return 0;
-}
-
-static size_t ds_get_index(struct ds_context *context, enum ds_qualifier qual)
-{
-	unsigned long base, index;
-
-	base  = ds_get(context->ds, qual, ds_buffer_base);
-	index = ds_get(context->ds, qual, ds_index);
-
-	return (index - base) / ds_cfg.sizeof_rec[qual];
 }
 
-int ds_get_bts_index(struct bts_tracer *tracer, size_t *pos)
+void ds_suspend_bts(struct bts_tracer *tracer)
 {
-	if (!tracer)
-		return -EINVAL;
+	struct task_struct *task;
 
-	if (!pos)
-		return -EINVAL;
-
-	*pos = ds_get_index(tracer->ds.context, ds_bts);
-
-	return 0;
-}
-
-int ds_get_pebs_index(struct pebs_tracer *tracer, size_t *pos)
-{
 	if (!tracer)
-		return -EINVAL;
+		return;
 
-	if (!pos)
-		return -EINVAL;
+	task = tracer->ds.context->task;
 
-	*pos = ds_get_index(tracer->ds.context, ds_pebs);
+	if (!task || (task == current))
+		update_debugctlmsr(get_debugctlmsr() & ~BTS_CONTROL);
 
-	return 0;
-}
+	if (task) {
+		task->thread.debugctlmsr &= ~BTS_CONTROL;
 
-static size_t ds_get_end(struct ds_context *context, enum ds_qualifier qual)
-{
-	unsigned long base, max;
-
-	base = ds_get(context->ds, qual, ds_buffer_base);
-	max  = ds_get(context->ds, qual, ds_absolute_maximum);
-
-	return (max - base) / ds_cfg.sizeof_rec[qual];
+		if (!task->thread.debugctlmsr)
+			clear_tsk_thread_flag(task, TIF_DEBUGCTLMSR);
+	}
 }
 
-int ds_get_bts_end(struct bts_tracer *tracer, size_t *pos)
+void ds_resume_bts(struct bts_tracer *tracer)
 {
-	if (!tracer)
-		return -EINVAL;
-
-	if (!pos)
-		return -EINVAL;
-
-	*pos = ds_get_end(tracer->ds.context, ds_bts);
-
-	return 0;
-}
+	struct task_struct *task;
+	unsigned long control;
 
-int ds_get_pebs_end(struct pebs_tracer *tracer, size_t *pos)
-{
 	if (!tracer)
-		return -EINVAL;
-
-	if (!pos)
-		return -EINVAL;
-
-	*pos = ds_get_end(tracer->ds.context, ds_pebs);
-
-	return 0;
-}
-
-static int ds_access(struct ds_context *context, enum ds_qualifier qual,
-		     size_t index, const void **record)
-{
-	unsigned long base, idx;
-
-	if (!record)
-		return -EINVAL;
-
-	base = ds_get(context->ds, qual, ds_buffer_base);
-	idx = base + (index * ds_cfg.sizeof_rec[qual]);
-
-	if (idx > ds_get(context->ds, qual, ds_absolute_maximum))
-		return -EINVAL;
+		return;
 
-	*record = (const void *)idx;
+	task = tracer->ds.context->task;
 
-	return ds_cfg.sizeof_rec[qual];
-}
+	control = ds_cfg.ctl[dsf_bts];
+	if (!(tracer->trace.ds.flags & BTS_KERNEL))
+		control |= ds_cfg.ctl[dsf_bts_kernel];
+	if (!(tracer->trace.ds.flags & BTS_USER))
+		control |= ds_cfg.ctl[dsf_bts_user];
 
-int ds_access_bts(struct bts_tracer *tracer, size_t index,
-		  const void **record)
-{
-	if (!tracer)
-		return -EINVAL;
+	if (task) {
+		task->thread.debugctlmsr |= control;
+		set_tsk_thread_flag(task, TIF_DEBUGCTLMSR);
+	}
 
-	return ds_access(tracer->ds.context, ds_bts, index, record);
+	if (!task || (task == current))
+		update_debugctlmsr(get_debugctlmsr() | control);
 }
 
-int ds_access_pebs(struct pebs_tracer *tracer, size_t index,
-		   const void **record)
+void ds_release_pebs(struct pebs_tracer *tracer)
 {
 	if (!tracer)
-		return -EINVAL;
-
-	return ds_access(tracer->ds.context, ds_pebs, index, record);
-}
-
-static int ds_write(struct ds_context *context, enum ds_qualifier qual,
-		    const void *record, size_t size)
-{
-	int bytes_written = 0;
-
-	if (!record)
-		return -EINVAL;
-
-	while (size) {
-		unsigned long base, index, end, write_end, int_th;
-		unsigned long write_size, adj_write_size;
-
-		/*
-		 * write as much as possible without producing an
-		 * overflow interrupt.
-		 *
-		 * interrupt_threshold must either be
-		 * - bigger than absolute_maximum or
-		 * - point to a record between buffer_base and absolute_maximum
-		 *
-		 * index points to a valid record.
-		 */
-		base   = ds_get(context->ds, qual, ds_buffer_base);
-		index  = ds_get(context->ds, qual, ds_index);
-		end    = ds_get(context->ds, qual, ds_absolute_maximum);
-		int_th = ds_get(context->ds, qual, ds_interrupt_threshold);
-
-		write_end = min(end, int_th);
-
-		/* if we are already beyond the interrupt threshold,
-		 * we fill the entire buffer */
-		if (write_end <= index)
-			write_end = end;
-
-		if (write_end <= index)
-			break;
-
-		write_size = min((unsigned long) size, write_end - index);
-		memcpy((void *)index, record, write_size);
-
-		record = (const char *)record + write_size;
-		size -= write_size;
-		bytes_written += write_size;
-
-		adj_write_size = write_size / ds_cfg.sizeof_rec[qual];
-		adj_write_size *= ds_cfg.sizeof_rec[qual];
-
-		/* zero out trailing bytes */
-		memset((char *)index + write_size, 0,
-		       adj_write_size - write_size);
-		index += adj_write_size;
+		return;
 
-		if (index >= end)
-			index = base;
-		ds_set(context->ds, qual, ds_index, index);
+	ds_suspend_pebs(tracer);
 
-		if (index >= int_th)
-			ds_overflow(context, qual);
-	}
+	WARN_ON_ONCE(tracer->ds.context->pebs_master != tracer);
+	tracer->ds.context->pebs_master = NULL;
 
-	return bytes_written;
-}
+	put_tracer(tracer->ds.context->task);
+	ds_put_context(tracer->ds.context);
 
-int ds_write_bts(struct bts_tracer *tracer, const void *record, size_t size)
-{
-	if (!tracer)
-		return -EINVAL;
-
-	return ds_write(tracer->ds.context, ds_bts, record, size);
+	kfree(tracer);
 }
 
-int ds_write_pebs(struct pebs_tracer *tracer, const void *record, size_t size)
+void ds_suspend_pebs(struct pebs_tracer *tracer)
 {
-	if (!tracer)
-		return -EINVAL;
 
-	return ds_write(tracer->ds.context, ds_pebs, record, size);
 }
 
-static void ds_reset_or_clear(struct ds_context *context,
-			      enum ds_qualifier qual, int clear)
+void ds_resume_pebs(struct pebs_tracer *tracer)
 {
-	unsigned long base, end;
-
-	base = ds_get(context->ds, qual, ds_buffer_base);
-	end  = ds_get(context->ds, qual, ds_absolute_maximum);
-
-	if (clear)
-		memset((void *)base, 0, end - base);
 
-	ds_set(context->ds, qual, ds_index, base);
 }
 
-int ds_reset_bts(struct bts_tracer *tracer)
+const struct bts_trace *ds_read_bts(struct bts_tracer *tracer)
 {
 	if (!tracer)
-		return -EINVAL;
-
-	ds_reset_or_clear(tracer->ds.context, ds_bts, /* clear = */ 0);
+		return NULL;
 
-	return 0;
+	ds_read_config(tracer->ds.context, &tracer->trace.ds, ds_bts);
+	return &tracer->trace;
 }
 
-int ds_reset_pebs(struct pebs_tracer *tracer)
+const struct pebs_trace *ds_read_pebs(struct pebs_tracer *tracer)
 {
 	if (!tracer)
-		return -EINVAL;
+		return NULL;
 
-	ds_reset_or_clear(tracer->ds.context, ds_pebs, /* clear = */ 0);
+	ds_read_config(tracer->ds.context, &tracer->trace.ds, ds_pebs);
+	tracer->trace.reset_value =
+		*(u64 *)(tracer->ds.context->ds + (ds_cfg.sizeof_field * 8));
 
-	return 0;
+	return &tracer->trace;
 }
 
-int ds_clear_bts(struct bts_tracer *tracer)
+int ds_reset_bts(struct bts_tracer *tracer)
 {
 	if (!tracer)
 		return -EINVAL;
 
-	ds_reset_or_clear(tracer->ds.context, ds_bts, /* clear = */ 1);
-
-	return 0;
-}
-
-int ds_clear_pebs(struct pebs_tracer *tracer)
-{
-	if (!tracer)
-		return -EINVAL;
+	tracer->trace.ds.top = tracer->trace.ds.begin;
 
-	ds_reset_or_clear(tracer->ds.context, ds_pebs, /* clear = */ 1);
+	ds_set(tracer->ds.context->ds, ds_bts, ds_index,
+	       (unsigned long)tracer->trace.ds.top);
 
 	return 0;
 }
 
-int ds_get_pebs_reset(struct pebs_tracer *tracer, u64 *value)
+int ds_reset_pebs(struct pebs_tracer *tracer)
 {
 	if (!tracer)
 		return -EINVAL;
 
-	if (!value)
-		return -EINVAL;
+	tracer->trace.ds.top = tracer->trace.ds.begin;
 
-	*value = *(u64 *)(tracer->ds.context->ds + (ds_cfg.sizeof_field * 8));
+	ds_set(tracer->ds.context->ds, ds_bts, ds_index,
+	       (unsigned long)tracer->trace.ds.top);
 
 	return 0;
 }
@@ -746,35 +894,59 @@ int ds_set_pebs_reset(struct pebs_tracer *tracer, u64 value)
 	return 0;
 }
 
-static const struct ds_configuration ds_cfg_var = {
-	.sizeof_ds    = sizeof(long) * 12,
-	.sizeof_field = sizeof(long),
-	.sizeof_rec[ds_bts]   = sizeof(long) * 3,
+static const struct ds_configuration ds_cfg_netburst = {
+	.name = "netburst",
+	.ctl[dsf_bts]		= (1 << 2) | (1 << 3),
+	.ctl[dsf_bts_kernel]	= (1 << 5),
+	.ctl[dsf_bts_user]	= (1 << 6),
+
+	.sizeof_field		= sizeof(long),
+	.sizeof_rec[ds_bts]	= sizeof(long) * 3,
 #ifdef __i386__
-	.sizeof_rec[ds_pebs]  = sizeof(long) * 10
+	.sizeof_rec[ds_pebs]	= sizeof(long) * 10,
 #else
-	.sizeof_rec[ds_pebs]  = sizeof(long) * 18
+	.sizeof_rec[ds_pebs]	= sizeof(long) * 18,
 #endif
 };
-static const struct ds_configuration ds_cfg_64 = {
-	.sizeof_ds    = 8 * 12,
-	.sizeof_field = 8,
-	.sizeof_rec[ds_bts]   = 8 * 3,
+static const struct ds_configuration ds_cfg_pentium_m = {
+	.name = "pentium m",
+	.ctl[dsf_bts]		= (1 << 6) | (1 << 7),
+
+	.sizeof_field		= sizeof(long),
+	.sizeof_rec[ds_bts]	= sizeof(long) * 3,
 #ifdef __i386__
-	.sizeof_rec[ds_pebs]  = 8 * 10
+	.sizeof_rec[ds_pebs]	= sizeof(long) * 10,
 #else
-	.sizeof_rec[ds_pebs]  = 8 * 18
+	.sizeof_rec[ds_pebs]	= sizeof(long) * 18,
 #endif
 };
+static const struct ds_configuration ds_cfg_core2 = {
+	.name = "core 2",
+	.ctl[dsf_bts]		= (1 << 6) | (1 << 7),
+	.ctl[dsf_bts_kernel]	= (1 << 9),
+	.ctl[dsf_bts_user]	= (1 << 10),
+
+	.sizeof_field		= 8,
+	.sizeof_rec[ds_bts]	= 8 * 3,
+	.sizeof_rec[ds_pebs]	= 8 * 18,
+};
 
-static inline void
+static void
 ds_configure(const struct ds_configuration *cfg)
 {
+	memset(&ds_cfg, 0, sizeof(ds_cfg));
 	ds_cfg = *cfg;
 
-	printk(KERN_INFO "DS available\n");
+	printk(KERN_INFO "[ds] using %s configuration\n", ds_cfg.name);
+
+	if (!cpu_has_bts) {
+		ds_cfg.ctl[dsf_bts] = 0;
+		printk(KERN_INFO "[ds] bts not available\n");
+	}
+	if (!cpu_has_pebs)
+		printk(KERN_INFO "[ds] pebs not available\n");
 
-	WARN_ON_ONCE(MAX_SIZEOF_DS < ds_cfg.sizeof_ds);
+	WARN_ON_ONCE(MAX_SIZEOF_DS < (12 * ds_cfg.sizeof_field));
 }
 
 void __cpuinit ds_init_intel(struct cpuinfo_x86 *c)
@@ -787,10 +959,10 @@ void __cpuinit ds_init_intel(struct cpuinfo_x86 *c)
 			break;
 		case 0xD:
 		case 0xE: /* Pentium M */
-			ds_configure(&ds_cfg_var);
+			ds_configure(&ds_cfg_pentium_m);
 			break;
 		default: /* Core2, Atom, ... */
-			ds_configure(&ds_cfg_64);
+			ds_configure(&ds_cfg_core2);
 			break;
 		}
 		break;
@@ -799,7 +971,7 @@ void __cpuinit ds_init_intel(struct cpuinfo_x86 *c)
 		case 0x0:
 		case 0x1:
 		case 0x2: /* Netburst */
-			ds_configure(&ds_cfg_var);
+			ds_configure(&ds_cfg_netburst);
 			break;
 		default:
 			/* sorry, don't know about them */
@@ -812,14 +984,41 @@ void __cpuinit ds_init_intel(struct cpuinfo_x86 *c)
 	}
 }
 
-void ds_free(struct ds_context *context)
+/*
+ * Change the DS configuration from tracing prev to tracing next.
+ */
+void ds_switch_to(struct task_struct *prev, struct task_struct *next)
 {
-	/* This is called when the task owning the parameter context
-	 * is dying. There should not be any user of that context left
-	 * to disturb us, anymore. */
-	unsigned long leftovers = context->count;
-	while (leftovers--) {
-		put_tracer(context->task);
-		ds_put_context(context);
+	struct ds_context *prev_ctx = prev->thread.ds_ctx;
+	struct ds_context *next_ctx = next->thread.ds_ctx;
+
+	if (prev_ctx) {
+		update_debugctlmsr(0);
+
+		if (prev_ctx->bts_master &&
+		    (prev_ctx->bts_master->trace.ds.flags & BTS_TIMESTAMPS)) {
+			struct bts_struct ts = {
+				.qualifier = bts_task_departs,
+				.variant.timestamp.jiffies = jiffies_64,
+				.variant.timestamp.pid = prev->pid
+			};
+			bts_write(prev_ctx->bts_master, &ts);
+		}
+	}
+
+	if (next_ctx) {
+		if (next_ctx->bts_master &&
+		    (next_ctx->bts_master->trace.ds.flags & BTS_TIMESTAMPS)) {
+			struct bts_struct ts = {
+				.qualifier = bts_task_arrives,
+				.variant.timestamp.jiffies = jiffies_64,
+				.variant.timestamp.pid = next->pid
+			};
+			bts_write(next_ctx->bts_master, &ts);
+		}
+
+		wrmsrl(MSR_IA32_DS_AREA, (unsigned long)next_ctx->ds);
 	}
+
+	update_debugctlmsr(next->thread.debugctlmsr);
 }