// 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 { … }; /* * Per-CPU constraints data. */ struct bp_cpuinfo { … }; 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) { … } /* 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 = …; 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(…); /* * 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) { … } static struct mutex *bp_constraints_lock(struct perf_event *bp) { … } static void bp_constraints_unlock(struct mutex *tsk_mtx) { … } static bool bp_constraints_is_locked(struct perf_event *bp) { … } static inline void assert_bp_constraints_lock_held(struct perf_event *bp) { … } #ifdef hw_breakpoint_slots /* * Number of breakpoint slots is constant, and the same for all types. */ static_assert(…); static inline int hw_breakpoint_slots_cached(int type) { … } static inline int init_breakpoint_slots(void) { … } #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) { … } static int bp_slots_histogram_max(struct bp_slots_histogram *hist, enum bp_type_idx type) { … } static int bp_slots_histogram_max_merge(struct bp_slots_histogram *hist1, struct bp_slots_histogram *hist2, enum bp_type_idx type) { … } #ifndef hw_breakpoint_weight static inline int hw_breakpoint_weight(struct perf_event *bp) { … } #endif static inline enum bp_type_idx find_slot_idx(u64 bp_type) { … } /* * 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) { … } /* * 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) { … } static const struct cpumask *cpumask_of_bp(struct perf_event *bp) { … } /* * 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) { … } /* * 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) { … } /* * 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) { … } int reserve_bp_slot(struct perf_event *bp) { … } static void __release_bp_slot(struct perf_event *bp, u64 bp_type) { … } void release_bp_slot(struct perf_event *bp) { … } static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type) { … } static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type) { … } /* * 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 dbg_release_bp_slot(struct perf_event *bp) { … } static int hw_breakpoint_parse(struct perf_event *bp, const struct perf_event_attr *attr, struct arch_hw_breakpoint *hw) { … } int register_perf_hw_breakpoint(struct perf_event *bp) { … } /** * 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) { … } EXPORT_SYMBOL_GPL(…); static void hw_breakpoint_copy_attr(struct perf_event_attr *to, struct perf_event_attr *from) { … } int modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr, bool check) { … } /** * 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) { … } EXPORT_SYMBOL_GPL(…); /** * unregister_hw_breakpoint - unregister a user-space hardware breakpoint * @bp: the breakpoint structure to unregister */ void unregister_hw_breakpoint(struct perf_event *bp) { … } EXPORT_SYMBOL_GPL(…); /** * 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) { … } EXPORT_SYMBOL_GPL(…); /** * 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) { … } EXPORT_SYMBOL_GPL(…); /** * hw_breakpoint_is_used - check if breakpoints are currently used * * Returns: true if breakpoints are used, false otherwise. */ bool hw_breakpoint_is_used(void) { … } static struct notifier_block hw_breakpoint_exceptions_nb = …; static void bp_perf_event_destroy(struct perf_event *event) { … } static int hw_breakpoint_event_init(struct perf_event *bp) { … } static int hw_breakpoint_add(struct perf_event *bp, int flags) { … } static void hw_breakpoint_del(struct perf_event *bp, int flags) { … } static void hw_breakpoint_start(struct perf_event *bp, int flags) { … } static void hw_breakpoint_stop(struct perf_event *bp, int flags) { … } static struct pmu perf_breakpoint = …; int __init init_hw_breakpoint(void) { … }
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