/*
* Debug Store support
*
* This provides a low-level interface to the hardware's Debug Store
* feature that is used for branch trace store (BTS) and
* precise-event based sampling (PEBS).
*
* It manages:
* - per-thread and per-cpu allocation of BTS and PEBS
* - buffer memory allocation (optional)
* - buffer overflow handling
* - buffer access
*
* It assumes:
* - get_task_struct on all parameter tasks
* - current is allowed to trace parameter tasks
*
*
* Copyright (C) 2007-2008 Intel Corporation.
* Markus Metzger <markus.t.metzger@intel.com>, 2007-2008
*/
#ifdef CONFIG_X86_DS
#include <asm/ds.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/mm.h>
/*
* 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. */
unsigned char sizeof_field;
/* the size of a BTS/PEBS record in bytes */
unsigned char sizeof_rec[2];
};
static struct ds_configuration ds_cfg;
/*
* 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
*
* 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
* - an offset giving the start of the respective region
*
* This offset is further used to index various arrays holding
* information for BTS and PEBS at the respective index.
*
* On later 32bit processors, we only access the lower 32bit of the
* 64bit pointer fields. The upper halves will be zeroed out.
*/
enum ds_field {
ds_buffer_base = 0,
ds_index,
ds_absolute_maximum,
ds_interrupt_threshold,
};
enum ds_qualifier {
ds_bts = 0,
ds_pebs
};
static inline unsigned long ds_get(const unsigned char *base,
enum ds_qualifier qual, enum ds_field field)
{
base += (ds_cfg.sizeof_field * (field + (4 * qual)));
return *(unsigned long *)base;
}
static inline void ds_set(unsigned char *base, enum ds_qualifier qual,
enum ds_field field, unsigned long value)
{
base += (ds_cfg.sizeof_field * (field + (4 * qual)));
(*(unsigned long *)base) = value;
}
/*
* Locking is done only for allocating BTS or PEBS resources and for
* guarding context and buffer memory allocation.
*
* Most functions require the current task to own the ds context part
* they are going to access. All the locking is done when validating
* access to the context.
*/
static spinlock_t ds_lock = __SPIN_LOCK_UNLOCKED(ds_lock);
/*
* Validate that the current task is allowed to access the BTS/PEBS
* buffer of the parameter task.
*
* Returns 0, if access is granted; -Eerrno, otherwise.
*/
static inline int ds_validate_access(struct ds_context *context,
enum ds_qualifier qual)
{
if (!context)
return -EPERM;
if (context->owner[qual] == current)
return 0;
return -EPERM;
}
/*
* We either support (system-wide) per-cpu or per-thread allocation.
* We distinguish the two based on the task_struct pointer, where a
* NULL pointer indicates per-cpu allocation for the current cpu.
*
* Allocations are use-counted. As soon as resources are allocated,
* further allocations must be of the same type (per-cpu or
* per-thread). We model this by counting allocations (i.e. the number
* of tracers of a certain type) for one type negatively:
* =0 no tracers
* >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 inline void get_tracer(struct task_struct *task)
{
tracers += (task ? 1 : -1);
}
static inline void put_tracer(struct task_struct *task)
{
tracers -= (task ? 1 : -1);
}
static inline int check_tracer(struct task_struct *task)
{
return (task ? (tracers >= 0) : (tracers <= 0));
}
/*
* The DS context is either attached to a thread or to a cpu:
* - in the former case, the thread_struct contains a pointer to the
* attached context.
* - in the latter case, we use a static array of per-cpu context
* pointers.
*
* Contexts are use-counted. They are allocated on first access and
* deallocated when the last user puts the context.
*
* We distinguish between an allocating and a non-allocating get of a
* context:
* - the allocating get is used for requesting BTS/PEBS resources. It
* requires the caller to hold the global ds_lock.
* - the non-allocating get is used for all other cases. A
* non-existing context indicates an error. It acquires and releases
* the ds_lock itself for obtaining the context.
*
* A context and its DS configuration are allocated and deallocated
* together. A context always has a DS configuration of the
* appropriate size.
*/
static DEFINE_PER_CPU(struct ds_context *, system_context);
#define this_system_context per_cpu(system_context, smp_processor_id())
/*
* Returns the pointer to the parameter task's context or to the
* system-wide context, if task is NULL.
*
* Increases the use count of the returned context, if not NULL.
*/
static inline struct ds_context *ds_get_context(struct task_struct *task)
{
struct ds_context *context;
spin_lock(&ds_lock);
context = (task ? task->thread.ds_ctx : this_system_context);
if (context)
context->count++;
spin_unlock(&ds_lock);
return context;
}
/*
* Same as ds_get_context, but allocates the context and it's DS
* structure, if necessary; returns NULL; if out of memory.
*
* pre: requires ds_lock to be held
*/
static inline struct ds_context *ds_alloc_context(struct task_struct *task)
{
struct ds_context **p_context =
(task ? &task->thread.ds_ctx : &this_system_context);
struct ds_context *context = *p_context;
if (!context) {
context = kzalloc(sizeof(*context), GFP_KERNEL);
if (!context)
return NULL;
context->ds = kzalloc(ds_cfg.sizeof_ds, GFP_KERNEL);
if (!context->ds) {
kfree(context);
return NULL;
}
*p_context = context;
context->this = p_context;
context->task = task;
if (task)
set_tsk_thread_flag(task, TIF_DS_AREA_MSR);
if (!task || (task == current))
wrmsr(MSR_IA32_DS_AREA, (unsigned long)context->ds, 0);
get_tracer(task);
}
context->count++;
return context;
}
/*
* Decreases the use count of the parameter context, if not NULL.
* Deallocates the context, if the use count reaches zero.
*/
static inline void ds_put_context(struct ds_context *context)
{
if (!context)
return;
spin_lock(&ds_lock);
if (--context->count)
goto out;
*(context->this) = NULL;
if (context->task)
clear_tsk_thread_flag(context->task, TIF_DS_AREA_MSR);
if (!context->task || (context->task == current))
wrmsrl(MSR_IA32_DS_AREA, 0);
put_tracer(context->task);
/* free any leftover buffers from tracers that did not
* deallocate them properly. */
kfree(context->buffer[ds_bts]);
kfree(context->buffer[ds_pebs]);
kfree(context->ds);
kfree(context);
out:
spin_unlock(&ds_lock);
}
/*
* Handle a buffer overflow
*
* task: the task whose buffers are overflowing;
* NULL for a buffer overflow on the current cpu
* context: the ds context
* qual: the buffer type
*/
static void ds_overflow(struct task_struct *task, struct ds_context *context,
enum ds_qualifier qual)
{
if (!context)
return;
if (context->callback[qual])
(*context->callback[qual])(task);
/* todo: do some more overflow handling */
}
/*
* Allocate a non-pageable buffer of the parameter size.
* Checks the memory and the locked memory rlimit.
*
* Returns the buffer, if successful;
* NULL, if out of memory or rlimit exceeded.
*
* size: the requested buffer size in bytes
* pages (out): if not NULL, contains the number of pages reserved
*/
static inline void *ds_allocate_buffer(size_t size, unsigned int *pages)
{
unsigned long rlim, vm, pgsz;
void *buffer;
pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT;
rlim = current->signal->rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT;
vm = current->mm->total_vm + pgsz;
if (rlim < vm)
return NULL;
rlim = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur >> PAGE_SHIFT;
vm = current->mm->locked_vm + pgsz;
if (rlim < vm)
return NULL;
buffer = kzalloc(size, GFP_KERNEL);
if (!buffer)
return NULL;
current->mm->total_vm += pgsz;
current->mm->locked_vm += pgsz;
if (pages)
*pages = pgsz;
return buffer;
}
static int ds_request(struct task_struct *task, void *base, size_t size,
ds_ovfl_callback_t ovfl, enum ds_qualifier qual)
{
struct ds_context *context;
unsigned long buffer, adj;
const unsigned long alignment = (1 << 3);
int error = 0;
if (!ds_cfg.sizeof_ds)
return -EOPNOTSUPP;
/* we require some space to do alignment adjustments below */
if (size < (alignment + ds_cfg.sizeof_rec[qual]))
return -EINVAL;
/* buffer overflow notification is not yet implemented */
if (ovfl)
return -EOPNOTSUPP;
spin_lock(&ds_lock);
if (!check_tracer(task))
return -EPERM;
error = -ENOMEM;
context = ds_alloc_context(task);
if (!context)
goto out_unlock;
error = -EALREADY;
if (context->owner[qual] == current)
goto out_unlock;
error = -EPERM;
if (context->owner[qual] != NULL)
goto out_unlock;
context->owner[qual] = current;
spin_unlock(&ds_lock);
error = -ENOMEM;
if (!base) {
base = ds_allocate_buffer(size, &context->pages[qual]);
if (!base)
goto out_release;
context->buffer[qual] = base;
}
error = 0;
context->callback[qual] = ovfl;
/* adjust the buffer address and size to meet alignment
* constraints:
* - buffer is double-word aligned
* - size is multiple of record size
*
* We checked the size at the very beginning; we have enough
* space to do the adjustment.
*/
buffer = (unsigned long)base;
adj = ALIGN(buffer, alignment) - buffer;
buffer += adj;
size -= adj;
size /= ds_cfg.sizeof_rec[qual];
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);
if (ovfl) {
/* todo: select a suitable interrupt threshold */
} else
ds_set(context->ds, qual,
ds_interrupt_threshold, buffer + size + 1);
/* we keep the context until ds_release */
return error;
out_release:
context->owner[qual] = NULL;
ds_put_context(context);
return error;
out_unlock:
spin_unlock(&ds_lock);
ds_put_context(context);
return error;
}
int ds_request_bts(struct task_struct *task, void *base, size_t size,
ds_ovfl_callback_t ovfl)
{
return ds_request(task, base, size, ovfl, ds_bts);
}
int ds_request_pebs(struct task_struct *task, void *base, size_t size,
ds_ovfl_callback_t ovfl)
{
return ds_request(task, base, size, ovfl, ds_pebs);
}
static int ds_release(struct task_struct *task, enum ds_qualifier qual)
{
struct ds_context *context;
int error;
context = ds_get_context(task);
error = ds_validate_access(context, qual);
if (error < 0)
goto out;
kfree(context->buffer[qual]);
context->buffer[qual] = NULL;
current->mm->total_vm -= context->pages[qual];
current->mm->locked_vm -= context->pages[qual];
context->pages[qual] = 0;
context->owner[qual] = NULL;
/*
* we put the context twice:
* once for the ds_get_context
* once for the corresponding ds_request
*/
ds_put_context(context);
out:
ds_put_context(context);
return error;
}
int ds_release_bts(struct task_struct *task)
{
return ds_release(task, ds_bts);
}
int ds_release_pebs(struct task_struct *task)
{
return ds_release(task, ds_pebs);
}
static int ds_get_index(struct task_struct *task, size_t *pos,
enum ds_qualifier qual)
{
struct ds_context *context;
unsigned long base, index;
int error;
context = ds_get_context(task);
error = ds_validate_access(context, qual);
if (error < 0)
goto out;
base = ds_get(context->ds, qual, ds_buffer_base);
index = ds_get(context->ds, qual, ds_index);
error = ((index - base) / ds_cfg.sizeof_rec[qual]);
if (pos)
*pos = error;
out:
ds_put_context(context);
return error;
}
int ds_get_bts_index(struct task_struct *task, size_t *pos)
{
return ds_get_index(task, pos, ds_bts);
}
int ds_get_pebs_index(struct task_struct *task, size_t *pos)
{
return ds_get_index(task, pos, ds_pebs);
}
static int ds_get_end(struct task_struct *task, size_t *pos,
enum ds_qualifier qual)
{
struct ds_context *context;
unsigned long base, end;
int error;
context = ds_get_context(task);
error = ds_validate_access(context, qual);
if (error < 0)
goto out;
base = ds_get(context->ds, qual, ds_buffer_base);
end = ds_get(context->ds, qual, ds_absolute_maximum);
error = ((end - base) / ds_cfg.sizeof_rec[qual]);
if (pos)
*pos = error;
out:
ds_put_context(context);
return error;
}
int ds_get_bts_end(struct task_struct *task, size_t *pos)
{
return ds_get_end(task, pos, ds_bts);
}
int ds_get_pebs_end(struct task_struct *task, size_t *pos)
{
return ds_get_end(task, pos, ds_pebs);
}
static int ds_access(struct task_struct *task, size_t index,
const void **record, enum ds_qualifier qual)
{
struct ds_context *context;
unsigned long base, idx;
int error;
if (!record)
return -EINVAL;
context = ds_get_context(task);
error = ds_validate_access(context, qual);
if (error < 0)
goto out;
base = ds_get(context->ds, qual, ds_buffer_base);
idx = base + (index * ds_cfg.sizeof_rec[qual]);
error = -EINVAL;
if (idx > ds_get(context->ds, qual, ds_absolute_maximum))
goto out;
*record = (const void *)idx;
error = ds_cfg.sizeof_rec[qual];
out:
ds_put_context(context);
return error;
}
int ds_access_bts(struct task_struct *task, size_t index, const void **record)
{
return ds_access(task, index, record, ds_bts);
}
int ds_access_pebs(struct task_struct *task, size_t index, const void **record)
{
return ds_access(task, index, record, ds_pebs);
}
static int ds_write(struct task_struct *task, const void *record, size_t size,
enum ds_qualifier qual, int force)
{
struct ds_context *context;
int error;
if (!record)
return -EINVAL;
error = -EPERM;
context = ds_get_context(task);
if (!context)
goto out;
if (!force) {
error = ds_validate_access(context, qual);
if (error < 0)
goto out;
}
error = 0;
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)
goto out;
write_size = min((unsigned long) size, write_end - index);
memcpy((void *)index, record, write_size);
record = (const char *)record + write_size;
size -= write_size;
error += 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(task, context, qual);
}
out:
ds_put_context(context);
return error;
}
int ds_write_bts(struct task_struct *task, const void *record, size_t size)
{
return ds_write(task, record, size, ds_bts, /* force = */ 0);
}
int ds_write_pebs(struct task_struct *task, const void *record, size_t size)
{
return ds_write(task, record, size, ds_pebs, /* force = */ 0);
}
int ds_unchecked_write_bts(struct task_struct *task,
const void *record, size_t size)
{
return ds_write(task, record, size, ds_bts, /* force = */ 1);
}
int ds_unchecked_write_pebs(struct task_struct *task,
const void *record, size_t size)
{
return ds_write(task, record, size, ds_pebs, /* force = */ 1);
}
static int ds_reset_or_clear(struct task_struct *task,
enum ds_qualifier qual, int clear)
{
struct ds_context *context;
unsigned long base, end;
int error;
context = ds_get_context(task);
error = ds_validate_access(context, qual);
if (error < 0)
goto out;
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);
error = 0;
out:
ds_put_context(context);
return error;
}
int ds_reset_bts(struct task_struct *task)
{
return ds_reset_or_clear(task, ds_bts, /* clear = */ 0);
}
int ds_reset_pebs(struct task_struct *task)
{
return ds_reset_or_clear(task, ds_pebs, /* clear = */ 0);
}
int ds_clear_bts(struct task_struct *task)
{
return ds_reset_or_clear(task, ds_bts, /* clear = */ 1);
}
int ds_clear_pebs(struct task_struct *task)
{
return ds_reset_or_clear(task, ds_pebs, /* clear = */ 1);
}
int ds_get_pebs_reset(struct task_struct *task, u64 *value)
{
struct ds_context *context;
int error;
if (!value)
return -EINVAL;
context = ds_get_context(task);
error = ds_validate_access(context, ds_pebs);
if (error < 0)
goto out;
*value = *(u64 *)(context->ds + (ds_cfg.sizeof_field * 8));
error = 0;
out:
ds_put_context(context);
return error;
}
int ds_set_pebs_reset(struct task_struct *task, u64 value)
{
struct ds_context *context;
int error;
context = ds_get_context(task);
error = ds_validate_access(context, ds_pebs);
if (error < 0)
goto out;
*(u64 *)(context->ds + (ds_cfg.sizeof_field * 8)) = value;
error = 0;
out:
ds_put_context(context);
return error;
}
static const struct ds_configuration ds_cfg_var = {
.sizeof_ds = sizeof(long) * 12,
.sizeof_field = sizeof(long),
.sizeof_rec[ds_bts] = sizeof(long) * 3,
.sizeof_rec[ds_pebs] = sizeof(long) * 10
};
static const struct ds_configuration ds_cfg_64 = {
.sizeof_ds = 8 * 12,
.sizeof_field = 8,
.sizeof_rec[ds_bts] = 8 * 3,
.sizeof_rec[ds_pebs] = 8 * 10
};
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) {
case 0xD:
case 0xE: /* Pentium M */
ds_configure(&ds_cfg_var);
break;
case 0xF: /* Core2 */
case 0x1C: /* Atom */
ds_configure(&ds_cfg_64);
break;
default:
/* sorry, don't know about them */
break;
}
break;
case 0xF:
switch (c->x86_model) {
case 0x0:
case 0x1:
case 0x2: /* Netburst */
ds_configure(&ds_cfg_var);
break;
default:
/* sorry, don't know about them */
break;
}
break;
default:
/* sorry, don't know about them */
break;
}
}
void ds_free(struct ds_context *context)
{
/* 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--)
ds_put_context(context);
}
#endif /* CONFIG_X86_DS */
