diff options
Diffstat (limited to 'kernel/events/hw_breakpoint.c')
| -rw-r--r-- | kernel/events/hw_breakpoint.c | 1051 |
1 files changed, 1051 insertions, 0 deletions
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c new file mode 100644 index 000000000..c37977013 --- /dev/null +++ b/kernel/events/hw_breakpoint.c @@ -0,0 +1,1051 @@ +// 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; +} + +__weak int arch_reserve_bp_slot(struct perf_event *bp) +{ + return 0; +} + +__weak void arch_release_bp_slot(struct perf_event *bp) +{ +} + +/* + * Function to perform processor-specific cleanup during unregistration + */ +__weak void arch_unregister_hw_breakpoint(struct perf_event *bp) +{ + /* + * A weak stub function here for those archs that don't define + * it inside arch/.../kernel/hw_breakpoint.c + */ +} + +/* + * 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; + int ret; + + /* 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; + + ret = arch_reserve_bp_slot(bp); + if (ret) + return ret; + + 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; + + arch_release_bp_slot(bp); + + 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); + + arch_unregister_hw_breakpoint(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); +} |