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-rw-r--r--kernel/events/hw_breakpoint.c1023
1 files changed, 1023 insertions, 0 deletions
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
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index 0000000000..6c2cb4e4f4
--- /dev/null
+++ b/kernel/events/hw_breakpoint.c
@@ -0,0 +1,1023 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2007 Alan Stern
+ * Copyright (C) IBM Corporation, 2009
+ * Copyright (C) 2009, Frederic Weisbecker <fweisbec@gmail.com>
+ *
+ * Thanks to Ingo Molnar for his many suggestions.
+ *
+ * Authors: Alan Stern <stern@rowland.harvard.edu>
+ * K.Prasad <prasad@linux.vnet.ibm.com>
+ * Frederic Weisbecker <fweisbec@gmail.com>
+ */
+
+/*
+ * 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);
+}