// SPDX-License-Identifier: GPL-2.0+
/*
* Copyright (C) 2007 Alan Stern
* Copyright (C) IBM Corporation, 2009
* Copyright (C) 2009, Frederic Weisbecker <[email protected]>
*
* Thanks to Ingo Molnar for his many suggestions.
*
* Authors: Alan Stern <[email protected]>
* K.Prasad <[email protected]>
* Frederic Weisbecker <[email protected]>
*/
/*
* HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
* using the CPU's debug registers.
* This file contains the arch-independent routines.
*/
#include <linux/hw_breakpoint.h>
#include <linux/atomic.h>
#include <linux/bug.h>
#include <linux/cpu.h>
#include <linux/export.h>
#include <linux/init.h>
#include <linux/irqflags.h>
#include <linux/kdebug.h>
#include <linux/kernel.h>
#include <linux/mutex.h>
#include <linux/notifier.h>
#include <linux/percpu-rwsem.h>
#include <linux/percpu.h>
#include <linux/rhashtable.h>
#include <linux/sched.h>
#include <linux/slab.h>
/*
* Datastructure to track the total uses of N slots across tasks or CPUs;
* bp_slots_histogram::count[N] is the number of assigned N+1 breakpoint slots.
*/
struct bp_slots_histogram {
#ifdef hw_breakpoint_slots
atomic_t count[hw_breakpoint_slots(0)];
#else
atomic_t *count;
#endif
};
/*
* Per-CPU constraints data.
*/
struct bp_cpuinfo {
/* Number of pinned CPU breakpoints in a CPU. */
unsigned int cpu_pinned;
/* Histogram of pinned task breakpoints in a CPU. */
struct bp_slots_histogram tsk_pinned;
};
static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type)
{
return per_cpu_ptr(bp_cpuinfo + type, cpu);
}
/* Number of pinned CPU breakpoints globally. */
static struct bp_slots_histogram cpu_pinned[TYPE_MAX];
/* Number of pinned CPU-independent task breakpoints. */
static struct bp_slots_histogram tsk_pinned_all[TYPE_MAX];
/* Keep track of the breakpoints attached to tasks */
static struct rhltable task_bps_ht;
static const struct rhashtable_params task_bps_ht_params = {
.head_offset = offsetof(struct hw_perf_event, bp_list),
.key_offset = offsetof(struct hw_perf_event, target),
.key_len = sizeof_field(struct hw_perf_event, target),
.automatic_shrinking = true,
};
static bool constraints_initialized __ro_after_init;
/*
* Synchronizes accesses to the per-CPU constraints; the locking rules are:
*
* 1. Atomic updates to bp_cpuinfo::tsk_pinned only require a held read-lock
* (due to bp_slots_histogram::count being atomic, no update are lost).
*
* 2. Holding a write-lock is required for computations that require a
* stable snapshot of all bp_cpuinfo::tsk_pinned.
*
* 3. In all other cases, non-atomic accesses require the appropriately held
* lock (read-lock for read-only accesses; write-lock for reads/writes).
*/
DEFINE_STATIC_PERCPU_RWSEM(bp_cpuinfo_sem);
/*
* Return mutex to serialize accesses to per-task lists in task_bps_ht. Since
* rhltable synchronizes concurrent insertions/deletions, independent tasks may
* insert/delete concurrently; therefore, a mutex per task is sufficient.
*
* Uses task_struct::perf_event_mutex, to avoid extending task_struct with a
* hw_breakpoint-only mutex, which may be infrequently used. The caveat here is
* that hw_breakpoint may contend with per-task perf event list management. The
* assumption is that perf usecases involving hw_breakpoints are very unlikely
* to result in unnecessary contention.
*/
static inline struct mutex *get_task_bps_mutex(struct perf_event *bp)
{
struct task_struct *tsk = bp->hw.target;
return tsk ? &tsk->perf_event_mutex : NULL;
}
static struct mutex *bp_constraints_lock(struct perf_event *bp)
{
struct mutex *tsk_mtx = get_task_bps_mutex(bp);
if (tsk_mtx) {
/*
* Fully analogous to the perf_try_init_event() nesting
* argument in the comment near perf_event_ctx_lock_nested();
* this child->perf_event_mutex cannot ever deadlock against
* the parent->perf_event_mutex usage from
* perf_event_task_{en,dis}able().
*
* Specifically, inherited events will never occur on
* ->perf_event_list.
*/
mutex_lock_nested(tsk_mtx, SINGLE_DEPTH_NESTING);
percpu_down_read(&bp_cpuinfo_sem);
} else {
percpu_down_write(&bp_cpuinfo_sem);
}
return tsk_mtx;
}
static void bp_constraints_unlock(struct mutex *tsk_mtx)
{
if (tsk_mtx) {
percpu_up_read(&bp_cpuinfo_sem);
mutex_unlock(tsk_mtx);
} else {
percpu_up_write(&bp_cpuinfo_sem);
}
}
static bool bp_constraints_is_locked(struct perf_event *bp)
{
struct mutex *tsk_mtx = get_task_bps_mutex(bp);
return percpu_is_write_locked(&bp_cpuinfo_sem) ||
(tsk_mtx ? mutex_is_locked(tsk_mtx) :
percpu_is_read_locked(&bp_cpuinfo_sem));
}
static inline void assert_bp_constraints_lock_held(struct perf_event *bp)
{
struct mutex *tsk_mtx = get_task_bps_mutex(bp);
if (tsk_mtx)
lockdep_assert_held(tsk_mtx);
lockdep_assert_held(&bp_cpuinfo_sem);
}
#ifdef hw_breakpoint_slots
/*
* Number of breakpoint slots is constant, and the same for all types.
*/
static_assert(hw_breakpoint_slots(TYPE_INST) == hw_breakpoint_slots(TYPE_DATA));
static inline int hw_breakpoint_slots_cached(int type) { return hw_breakpoint_slots(type); }
static inline int init_breakpoint_slots(void) { return 0; }
#else
/*
* Dynamic number of breakpoint slots.
*/
static int __nr_bp_slots[TYPE_MAX] __ro_after_init;
static inline int hw_breakpoint_slots_cached(int type)
{
return __nr_bp_slots[type];
}
static __init bool
bp_slots_histogram_alloc(struct bp_slots_histogram *hist, enum bp_type_idx type)
{
hist->count = kcalloc(hw_breakpoint_slots_cached(type), sizeof(*hist->count), GFP_KERNEL);
return hist->count;
}
static __init void bp_slots_histogram_free(struct bp_slots_histogram *hist)
{
kfree(hist->count);
}
static __init int init_breakpoint_slots(void)
{
int i, cpu, err_cpu;
for (i = 0; i < TYPE_MAX; i++)
__nr_bp_slots[i] = hw_breakpoint_slots(i);
for_each_possible_cpu(cpu) {
for (i = 0; i < TYPE_MAX; i++) {
struct bp_cpuinfo *info = get_bp_info(cpu, i);
if (!bp_slots_histogram_alloc(&info->tsk_pinned, i))
goto err;
}
}
for (i = 0; i < TYPE_MAX; i++) {
if (!bp_slots_histogram_alloc(&cpu_pinned[i], i))
goto err;
if (!bp_slots_histogram_alloc(&tsk_pinned_all[i], i))
goto err;
}
return 0;
err:
for_each_possible_cpu(err_cpu) {
for (i = 0; i < TYPE_MAX; i++)
bp_slots_histogram_free(&get_bp_info(err_cpu, i)->tsk_pinned);
if (err_cpu == cpu)
break;
}
for (i = 0; i < TYPE_MAX; i++) {
bp_slots_histogram_free(&cpu_pinned[i]);
bp_slots_histogram_free(&tsk_pinned_all[i]);
}
return -ENOMEM;
}
#endif
static inline void
bp_slots_histogram_add(struct bp_slots_histogram *hist, int old, int val)
{
const int old_idx = old - 1;
const int new_idx = old_idx + val;
if (old_idx >= 0)
WARN_ON(atomic_dec_return_relaxed(&hist->count[old_idx]) < 0);
if (new_idx >= 0)
WARN_ON(atomic_inc_return_relaxed(&hist->count[new_idx]) < 0);
}
static int
bp_slots_histogram_max(struct bp_slots_histogram *hist, enum bp_type_idx type)
{
for (int i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) {
const int count = atomic_read(&hist->count[i]);
/* Catch unexpected writers; we want a stable snapshot. */
ASSERT_EXCLUSIVE_WRITER(hist->count[i]);
if (count > 0)
return i + 1;
WARN(count < 0, "inconsistent breakpoint slots histogram");
}
return 0;
}
static int
bp_slots_histogram_max_merge(struct bp_slots_histogram *hist1, struct bp_slots_histogram *hist2,
enum bp_type_idx type)
{
for (int i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) {
const int count1 = atomic_read(&hist1->count[i]);
const int count2 = atomic_read(&hist2->count[i]);
/* Catch unexpected writers; we want a stable snapshot. */
ASSERT_EXCLUSIVE_WRITER(hist1->count[i]);
ASSERT_EXCLUSIVE_WRITER(hist2->count[i]);
if (count1 + count2 > 0)
return i + 1;
WARN(count1 < 0, "inconsistent breakpoint slots histogram");
WARN(count2 < 0, "inconsistent breakpoint slots histogram");
}
return 0;
}
#ifndef hw_breakpoint_weight
static inline int hw_breakpoint_weight(struct perf_event *bp)
{
return 1;
}
#endif
static inline enum bp_type_idx find_slot_idx(u64 bp_type)
{
if (bp_type & HW_BREAKPOINT_RW)
return TYPE_DATA;
return TYPE_INST;
}
/*
* Return the maximum number of pinned breakpoints a task has in this CPU.
*/
static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
{
struct bp_slots_histogram *tsk_pinned = &get_bp_info(cpu, type)->tsk_pinned;
/*
* At this point we want to have acquired the bp_cpuinfo_sem as a
* writer to ensure that there are no concurrent writers in
* toggle_bp_task_slot() to tsk_pinned, and we get a stable snapshot.
*/
lockdep_assert_held_write(&bp_cpuinfo_sem);
return bp_slots_histogram_max_merge(tsk_pinned, &tsk_pinned_all[type], type);
}
/*
* Count the number of breakpoints of the same type and same task.
* The given event must be not on the list.
*
* If @cpu is -1, but the result of task_bp_pinned() is not CPU-independent,
* returns a negative value.
*/
static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
{
struct rhlist_head *head, *pos;
struct perf_event *iter;
int count = 0;
/*
* We need a stable snapshot of the per-task breakpoint list.
*/
assert_bp_constraints_lock_held(bp);
rcu_read_lock();
head = rhltable_lookup(&task_bps_ht, &bp->hw.target, task_bps_ht_params);
if (!head)
goto out;
rhl_for_each_entry_rcu(iter, pos, head, hw.bp_list) {
if (find_slot_idx(iter->attr.bp_type) != type)
continue;
if (iter->cpu >= 0) {
if (cpu == -1) {
count = -1;
goto out;
} else if (cpu != iter->cpu)
continue;
}
count += hw_breakpoint_weight(iter);
}
out:
rcu_read_unlock();
return count;
}
static const struct cpumask *cpumask_of_bp(struct perf_event *bp)
{
if (bp->cpu >= 0)
return cpumask_of(bp->cpu);
return cpu_possible_mask;
}
/*
* Returns the max pinned breakpoint slots in a given
* CPU (cpu > -1) or across all of them (cpu = -1).
*/
static int
max_bp_pinned_slots(struct perf_event *bp, enum bp_type_idx type)
{
const struct cpumask *cpumask = cpumask_of_bp(bp);
int pinned_slots = 0;
int cpu;
if (bp->hw.target && bp->cpu < 0) {
int max_pinned = task_bp_pinned(-1, bp, type);
if (max_pinned >= 0) {
/*
* Fast path: task_bp_pinned() is CPU-independent and
* returns the same value for any CPU.
*/
max_pinned += bp_slots_histogram_max(&cpu_pinned[type], type);
return max_pinned;
}
}
for_each_cpu(cpu, cpumask) {
struct bp_cpuinfo *info = get_bp_info(cpu, type);
int nr;
nr = info->cpu_pinned;
if (!bp->hw.target)
nr += max_task_bp_pinned(cpu, type);
else
nr += task_bp_pinned(cpu, bp, type);
pinned_slots = max(nr, pinned_slots);
}
return pinned_slots;
}
/*
* Add/remove the given breakpoint in our constraint table
*/
static int
toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type, int weight)
{
int cpu, next_tsk_pinned;
if (!enable)
weight = -weight;
if (!bp->hw.target) {
/*
* Update the pinned CPU slots, in per-CPU bp_cpuinfo and in the
* global histogram.
*/
struct bp_cpuinfo *info = get_bp_info(bp->cpu, type);
lockdep_assert_held_write(&bp_cpuinfo_sem);
bp_slots_histogram_add(&cpu_pinned[type], info->cpu_pinned, weight);
info->cpu_pinned += weight;
return 0;
}
/*
* If bp->hw.target, tsk_pinned is only modified, but not used
* otherwise. We can permit concurrent updates as long as there are no
* other uses: having acquired bp_cpuinfo_sem as a reader allows
* concurrent updates here. Uses of tsk_pinned will require acquiring
* bp_cpuinfo_sem as a writer to stabilize tsk_pinned's value.
*/
lockdep_assert_held_read(&bp_cpuinfo_sem);
/*
* Update the pinned task slots, in per-CPU bp_cpuinfo and in the global
* histogram. We need to take care of 4 cases:
*
* 1. This breakpoint targets all CPUs (cpu < 0), and there may only
* exist other task breakpoints targeting all CPUs. In this case we
* can simply update the global slots histogram.
*
* 2. This breakpoint targets a specific CPU (cpu >= 0), but there may
* only exist other task breakpoints targeting all CPUs.
*
* a. On enable: remove the existing breakpoints from the global
* slots histogram and use the per-CPU histogram.
*
* b. On disable: re-insert the existing breakpoints into the global
* slots histogram and remove from per-CPU histogram.
*
* 3. Some other existing task breakpoints target specific CPUs. Only
* update the per-CPU slots histogram.
*/
if (!enable) {
/*
* Remove before updating histograms so we can determine if this
* was the last task breakpoint for a specific CPU.
*/
int ret = rhltable_remove(&task_bps_ht, &bp->hw.bp_list, task_bps_ht_params);
if (ret)
return ret;
}
/*
* Note: If !enable, next_tsk_pinned will not count the to-be-removed breakpoint.
*/
next_tsk_pinned = task_bp_pinned(-1, bp, type);
if (next_tsk_pinned >= 0) {
if (bp->cpu < 0) { /* Case 1: fast path */
if (!enable)
next_tsk_pinned += hw_breakpoint_weight(bp);
bp_slots_histogram_add(&tsk_pinned_all[type], next_tsk_pinned, weight);
} else if (enable) { /* Case 2.a: slow path */
/* Add existing to per-CPU histograms. */
for_each_possible_cpu(cpu) {
bp_slots_histogram_add(&get_bp_info(cpu, type)->tsk_pinned,
0, next_tsk_pinned);
}
/* Add this first CPU-pinned task breakpoint. */
bp_slots_histogram_add(&get_bp_info(bp->cpu, type)->tsk_pinned,
next_tsk_pinned, weight);
/* Rebalance global task pinned histogram. */
bp_slots_histogram_add(&tsk_pinned_all[type], next_tsk_pinned,
-next_tsk_pinned);
} else { /* Case 2.b: slow path */
/* Remove this last CPU-pinned task breakpoint. */
bp_slots_histogram_add(&get_bp_info(bp->cpu, type)->tsk_pinned,
next_tsk_pinned + hw_breakpoint_weight(bp), weight);
/* Remove all from per-CPU histograms. */
for_each_possible_cpu(cpu) {
bp_slots_histogram_add(&get_bp_info(cpu, type)->tsk_pinned,
next_tsk_pinned, -next_tsk_pinned);
}
/* Rebalance global task pinned histogram. */
bp_slots_histogram_add(&tsk_pinned_all[type], 0, next_tsk_pinned);
}
} else { /* Case 3: slow path */
const struct cpumask *cpumask = cpumask_of_bp(bp);
for_each_cpu(cpu, cpumask) {
next_tsk_pinned = task_bp_pinned(cpu, bp, type);
if (!enable)
next_tsk_pinned += hw_breakpoint_weight(bp);
bp_slots_histogram_add(&get_bp_info(cpu, type)->tsk_pinned,
next_tsk_pinned, weight);
}
}
/*
* Readers want a stable snapshot of the per-task breakpoint list.
*/
assert_bp_constraints_lock_held(bp);
if (enable)
return rhltable_insert(&task_bps_ht, &bp->hw.bp_list, task_bps_ht_params);
return 0;
}
/*
* Constraints to check before allowing this new breakpoint counter.
*
* Note: Flexible breakpoints are currently unimplemented, but outlined in the
* below algorithm for completeness. The implementation treats flexible as
* pinned due to no guarantee that we currently always schedule flexible events
* before a pinned event in a same CPU.
*
* == Non-pinned counter == (Considered as pinned for now)
*
* - If attached to a single cpu, check:
*
* (per_cpu(info->flexible, cpu) || (per_cpu(info->cpu_pinned, cpu)
* + max(per_cpu(info->tsk_pinned, cpu)))) < HBP_NUM
*
* -> If there are already non-pinned counters in this cpu, it means
* there is already a free slot for them.
* Otherwise, we check that the maximum number of per task
* breakpoints (for this cpu) plus the number of per cpu breakpoint
* (for this cpu) doesn't cover every registers.
*
* - If attached to every cpus, check:
*
* (per_cpu(info->flexible, *) || (max(per_cpu(info->cpu_pinned, *))
* + max(per_cpu(info->tsk_pinned, *)))) < HBP_NUM
*
* -> This is roughly the same, except we check the number of per cpu
* bp for every cpu and we keep the max one. Same for the per tasks
* breakpoints.
*
*
* == Pinned counter ==
*
* - If attached to a single cpu, check:
*
* ((per_cpu(info->flexible, cpu) > 1) + per_cpu(info->cpu_pinned, cpu)
* + max(per_cpu(info->tsk_pinned, cpu))) < HBP_NUM
*
* -> Same checks as before. But now the info->flexible, if any, must keep
* one register at least (or they will never be fed).
*
* - If attached to every cpus, check:
*
* ((per_cpu(info->flexible, *) > 1) + max(per_cpu(info->cpu_pinned, *))
* + max(per_cpu(info->tsk_pinned, *))) < HBP_NUM
*/
static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
{
enum bp_type_idx type;
int max_pinned_slots;
int weight;
/* We couldn't initialize breakpoint constraints on boot */
if (!constraints_initialized)
return -ENOMEM;
/* Basic checks */
if (bp_type == HW_BREAKPOINT_EMPTY ||
bp_type == HW_BREAKPOINT_INVALID)
return -EINVAL;
type = find_slot_idx(bp_type);
weight = hw_breakpoint_weight(bp);
/* Check if this new breakpoint can be satisfied across all CPUs. */
max_pinned_slots = max_bp_pinned_slots(bp, type) + weight;
if (max_pinned_slots > hw_breakpoint_slots_cached(type))
return -ENOSPC;
return toggle_bp_slot(bp, true, type, weight);
}
int reserve_bp_slot(struct perf_event *bp)
{
struct mutex *mtx = bp_constraints_lock(bp);
int ret = __reserve_bp_slot(bp, bp->attr.bp_type);
bp_constraints_unlock(mtx);
return ret;
}
static void __release_bp_slot(struct perf_event *bp, u64 bp_type)
{
enum bp_type_idx type;
int weight;
type = find_slot_idx(bp_type);
weight = hw_breakpoint_weight(bp);
WARN_ON(toggle_bp_slot(bp, false, type, weight));
}
void release_bp_slot(struct perf_event *bp)
{
struct mutex *mtx = bp_constraints_lock(bp);
__release_bp_slot(bp, bp->attr.bp_type);
bp_constraints_unlock(mtx);
}
static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
{
int err;
__release_bp_slot(bp, old_type);
err = __reserve_bp_slot(bp, new_type);
if (err) {
/*
* Reserve the old_type slot back in case
* there's no space for the new type.
*
* This must succeed, because we just released
* the old_type slot in the __release_bp_slot
* call above. If not, something is broken.
*/
WARN_ON(__reserve_bp_slot(bp, old_type));
}
return err;
}
static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
{
struct mutex *mtx = bp_constraints_lock(bp);
int ret = __modify_bp_slot(bp, old_type, new_type);
bp_constraints_unlock(mtx);
return ret;
}
/*
* Allow the kernel debugger to reserve breakpoint slots without
* taking a lock using the dbg_* variant of for the reserve and
* release breakpoint slots.
*/
int dbg_reserve_bp_slot(struct perf_event *bp)
{
int ret;
if (bp_constraints_is_locked(bp))
return -1;
/* Locks aren't held; disable lockdep assert checking. */
lockdep_off();
ret = __reserve_bp_slot(bp, bp->attr.bp_type);
lockdep_on();
return ret;
}
int dbg_release_bp_slot(struct perf_event *bp)
{
if (bp_constraints_is_locked(bp))
return -1;
/* Locks aren't held; disable lockdep assert checking. */
lockdep_off();
__release_bp_slot(bp, bp->attr.bp_type);
lockdep_on();
return 0;
}
static int hw_breakpoint_parse(struct perf_event *bp,
const struct perf_event_attr *attr,
struct arch_hw_breakpoint *hw)
{
int err;
err = hw_breakpoint_arch_parse(bp, attr, hw);
if (err)
return err;
if (arch_check_bp_in_kernelspace(hw)) {
if (attr->exclude_kernel)
return -EINVAL;
/*
* Don't let unprivileged users set a breakpoint in the trap
* path to avoid trap recursion attacks.
*/
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
}
return 0;
}
int register_perf_hw_breakpoint(struct perf_event *bp)
{
struct arch_hw_breakpoint hw = { };
int err;
err = reserve_bp_slot(bp);
if (err)
return err;
err = hw_breakpoint_parse(bp, &bp->attr, &hw);
if (err) {
release_bp_slot(bp);
return err;
}
bp->hw.info = hw;
return 0;
}
/**
* register_user_hw_breakpoint - register a hardware breakpoint for user space
* @attr: breakpoint attributes
* @triggered: callback to trigger when we hit the breakpoint
* @context: context data could be used in the triggered callback
* @tsk: pointer to 'task_struct' of the process to which the address belongs
*/
struct perf_event *
register_user_hw_breakpoint(struct perf_event_attr *attr,
perf_overflow_handler_t triggered,
void *context,
struct task_struct *tsk)
{
return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
context);
}
EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
static void hw_breakpoint_copy_attr(struct perf_event_attr *to,
struct perf_event_attr *from)
{
to->bp_addr = from->bp_addr;
to->bp_type = from->bp_type;
to->bp_len = from->bp_len;
to->disabled = from->disabled;
}
int
modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
bool check)
{
struct arch_hw_breakpoint hw = { };
int err;
err = hw_breakpoint_parse(bp, attr, &hw);
if (err)
return err;
if (check) {
struct perf_event_attr old_attr;
old_attr = bp->attr;
hw_breakpoint_copy_attr(&old_attr, attr);
if (memcmp(&old_attr, attr, sizeof(*attr)))
return -EINVAL;
}
if (bp->attr.bp_type != attr->bp_type) {
err = modify_bp_slot(bp, bp->attr.bp_type, attr->bp_type);
if (err)
return err;
}
hw_breakpoint_copy_attr(&bp->attr, attr);
bp->hw.info = hw;
return 0;
}
/**
* modify_user_hw_breakpoint - modify a user-space hardware breakpoint
* @bp: the breakpoint structure to modify
* @attr: new breakpoint attributes
*/
int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
{
int err;
/*
* modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
* will not be possible to raise IPIs that invoke __perf_event_disable.
* So call the function directly after making sure we are targeting the
* current task.
*/
if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
perf_event_disable_local(bp);
else
perf_event_disable(bp);
err = modify_user_hw_breakpoint_check(bp, attr, false);
if (!bp->attr.disabled)
perf_event_enable(bp);
return err;
}
EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
/**
* unregister_hw_breakpoint - unregister a user-space hardware breakpoint
* @bp: the breakpoint structure to unregister
*/
void unregister_hw_breakpoint(struct perf_event *bp)
{
if (!bp)
return;
perf_event_release_kernel(bp);
}
EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
/**
* register_wide_hw_breakpoint - register a wide breakpoint in the kernel
* @attr: breakpoint attributes
* @triggered: callback to trigger when we hit the breakpoint
* @context: context data could be used in the triggered callback
*
* @return a set of per_cpu pointers to perf events
*/
struct perf_event * __percpu *
register_wide_hw_breakpoint(struct perf_event_attr *attr,
perf_overflow_handler_t triggered,
void *context)
{
struct perf_event * __percpu *cpu_events, *bp;
long err = 0;
int cpu;
cpu_events = alloc_percpu(typeof(*cpu_events));
if (!cpu_events)
return (void __percpu __force *)ERR_PTR(-ENOMEM);
cpus_read_lock();
for_each_online_cpu(cpu) {
bp = perf_event_create_kernel_counter(attr, cpu, NULL,
triggered, context);
if (IS_ERR(bp)) {
err = PTR_ERR(bp);
break;
}
per_cpu(*cpu_events, cpu) = bp;
}
cpus_read_unlock();
if (likely(!err))
return cpu_events;
unregister_wide_hw_breakpoint(cpu_events);
return (void __percpu __force *)ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
/**
* unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
* @cpu_events: the per cpu set of events to unregister
*/
void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
{
int cpu;
for_each_possible_cpu(cpu)
unregister_hw_breakpoint(per_cpu(*cpu_events, cpu));
free_percpu(cpu_events);
}
EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
/**
* hw_breakpoint_is_used - check if breakpoints are currently used
*
* Returns: true if breakpoints are used, false otherwise.
*/
bool hw_breakpoint_is_used(void)
{
int cpu;
if (!constraints_initialized)
return false;
for_each_possible_cpu(cpu) {
for (int type = 0; type < TYPE_MAX; ++type) {
struct bp_cpuinfo *info = get_bp_info(cpu, type);
if (info->cpu_pinned)
return true;
for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) {
if (atomic_read(&info->tsk_pinned.count[slot]))
return true;
}
}
}
for (int type = 0; type < TYPE_MAX; ++type) {
for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) {
/*
* Warn, because if there are CPU pinned counters,
* should never get here; bp_cpuinfo::cpu_pinned should
* be consistent with the global cpu_pinned histogram.
*/
if (WARN_ON(atomic_read(&cpu_pinned[type].count[slot])))
return true;
if (atomic_read(&tsk_pinned_all[type].count[slot]))
return true;
}
}
return false;
}
static struct notifier_block hw_breakpoint_exceptions_nb = {
.notifier_call = hw_breakpoint_exceptions_notify,
/* we need to be notified first */
.priority = 0x7fffffff
};
static void bp_perf_event_destroy(struct perf_event *event)
{
release_bp_slot(event);
}
static int hw_breakpoint_event_init(struct perf_event *bp)
{
int err;
if (bp->attr.type != PERF_TYPE_BREAKPOINT)
return -ENOENT;
/*
* no branch sampling for breakpoint events
*/
if (has_branch_stack(bp))
return -EOPNOTSUPP;
err = register_perf_hw_breakpoint(bp);
if (err)
return err;
bp->destroy = bp_perf_event_destroy;
return 0;
}
static int hw_breakpoint_add(struct perf_event *bp, int flags)
{
if (!(flags & PERF_EF_START))
bp->hw.state = PERF_HES_STOPPED;
if (is_sampling_event(bp)) {
bp->hw.last_period = bp->hw.sample_period;
perf_swevent_set_period(bp);
}
return arch_install_hw_breakpoint(bp);
}
static void hw_breakpoint_del(struct perf_event *bp, int flags)
{
arch_uninstall_hw_breakpoint(bp);
}
static void hw_breakpoint_start(struct perf_event *bp, int flags)
{
bp->hw.state = 0;
}
static void hw_breakpoint_stop(struct perf_event *bp, int flags)
{
bp->hw.state = PERF_HES_STOPPED;
}
static struct pmu perf_breakpoint = {
.task_ctx_nr = perf_sw_context, /* could eventually get its own */
.event_init = hw_breakpoint_event_init,
.add = hw_breakpoint_add,
.del = hw_breakpoint_del,
.start = hw_breakpoint_start,
.stop = hw_breakpoint_stop,
.read = hw_breakpoint_pmu_read,
};
int __init init_hw_breakpoint(void)
{
int ret;
ret = rhltable_init(&task_bps_ht, &task_bps_ht_params);
if (ret)
return ret;
ret = init_breakpoint_slots();
if (ret)
return ret;
constraints_initialized = true;
perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
return register_die_notifier(&hw_breakpoint_exceptions_nb);
}
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