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);
 }