FreeBSD/Linux Kernel Cross Reference
sys/kernel/hw_breakpoint.c

     /*
      * This program is free software; you can redistribute it and/or modify
      * it under the terms of the GNU General Public License as published by
      * the Free Software Foundation; either version 2 of the License, or
      * (at your option) any later version.
      *
      * This program is distributed in the hope that it will be useful,
      * but WITHOUT ANY WARRANTY; without even the implied warranty of
      * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     * GNU General Public License for more details.
     *
     * You should have received a copy of the GNU General Public License
     * along with this program; if not, write to the Free Software
     * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
     *
     * 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/irqflags.h>
    #include <linux/kallsyms.h>
    #include <linux/notifier.h>
    #include <linux/kprobes.h>
    #include <linux/kdebug.h>
    #include <linux/kernel.h>
    #include <linux/module.h>
    #include <linux/percpu.h>
    #include <linux/sched.h>
    #include <linux/init.h>
    #include <linux/slab.h>
    #include <linux/list.h>
    #include <linux/cpu.h>
    #include <linux/smp.h>
    
    #include <linux/hw_breakpoint.h>
    
    
    /*
     * Constraints data
     */
    
    /* Number of pinned cpu breakpoints in a cpu */
    static DEFINE_PER_CPU(unsigned int, nr_cpu_bp_pinned[TYPE_MAX]);
    
    /* Number of pinned task breakpoints in a cpu */
    static DEFINE_PER_CPU(unsigned int *, nr_task_bp_pinned[TYPE_MAX]);
    
    /* Number of non-pinned cpu/task breakpoints in a cpu */
    static DEFINE_PER_CPU(unsigned int, nr_bp_flexible[TYPE_MAX]);
    
    static int nr_slots[TYPE_MAX];
    
    /* Keep track of the breakpoints attached to tasks */
    static LIST_HEAD(bp_task_head);
    
    static int constraints_initialized;
    
    /* Gather the number of total pinned and un-pinned bp in a cpuset */
    struct bp_busy_slots {
            unsigned int pinned;
            unsigned int flexible;
    };
    
    /* Serialize accesses to the above constraints */
    static DEFINE_MUTEX(nr_bp_mutex);
    
    __weak int hw_breakpoint_weight(struct perf_event *bp)
    {
            return 1;
    }
    
    static inline enum bp_type_idx find_slot_idx(struct perf_event *bp)
    {
            if (bp->attr.bp_type & HW_BREAKPOINT_RW)
                    return TYPE_DATA;
    
            return TYPE_INST;
    }
    
    /*
     * Report the maximum number of pinned breakpoints a task
     * have in this cpu
     */
    static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
    {
            int i;
           unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
   
           for (i = nr_slots[type] - 1; i >= 0; i--) {
                   if (tsk_pinned[i] > 0)
                           return i + 1;
           }
   
           return 0;
   }
   
   /*
    * Count the number of breakpoints of the same type and same task.
    * The given event must be not on the list.
    */
   static int task_bp_pinned(struct perf_event *bp, enum bp_type_idx type)
   {
           struct perf_event_context *ctx = bp->ctx;
           struct perf_event *iter;
           int count = 0;
   
           list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
                   if (iter->ctx == ctx && find_slot_idx(iter) == type)
                           count += hw_breakpoint_weight(iter);
           }
   
           return count;
   }
   
   /*
    * Report the number of pinned/un-pinned breakpoints we have in
    * a given cpu (cpu > -1) or in all of them (cpu = -1).
    */
   static void
   fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp,
                       enum bp_type_idx type)
   {
           int cpu = bp->cpu;
           struct task_struct *tsk = bp->ctx->task;
   
           if (cpu >= 0) {
                   slots->pinned = per_cpu(nr_cpu_bp_pinned[type], cpu);
                   if (!tsk)
                           slots->pinned += max_task_bp_pinned(cpu, type);
                   else
                           slots->pinned += task_bp_pinned(bp, type);
                   slots->flexible = per_cpu(nr_bp_flexible[type], cpu);
   
                   return;
           }
   
           for_each_online_cpu(cpu) {
                   unsigned int nr;
   
                   nr = per_cpu(nr_cpu_bp_pinned[type], cpu);
                   if (!tsk)
                           nr += max_task_bp_pinned(cpu, type);
                   else
                           nr += task_bp_pinned(bp, type);
   
                   if (nr > slots->pinned)
                           slots->pinned = nr;
   
                   nr = per_cpu(nr_bp_flexible[type], cpu);
   
                   if (nr > slots->flexible)
                           slots->flexible = nr;
           }
   }
   
   /*
    * For now, continue to consider flexible as pinned, until we can
    * ensure no flexible event can ever be scheduled before a pinned event
    * in a same cpu.
    */
   static void
   fetch_this_slot(struct bp_busy_slots *slots, int weight)
   {
           slots->pinned += weight;
   }
   
   /*
    * Add a pinned breakpoint for the given task in our constraint table
    */
   static void toggle_bp_task_slot(struct perf_event *bp, int cpu, bool enable,
                                   enum bp_type_idx type, int weight)
   {
           unsigned int *tsk_pinned;
           int old_count = 0;
           int old_idx = 0;
           int idx = 0;
   
           old_count = task_bp_pinned(bp, type);
           old_idx = old_count - 1;
           idx = old_idx + weight;
   
           /* tsk_pinned[n] is the number of tasks having n breakpoints */
           tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
           if (enable) {
                   tsk_pinned[idx]++;
                   if (old_count > 0)
                           tsk_pinned[old_idx]--;
           } else {
                   tsk_pinned[idx]--;
                   if (old_count > 0)
                           tsk_pinned[old_idx]++;
           }
   }
   
   /*
    * Add/remove the given breakpoint in our constraint table
    */
   static void
   toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
                  int weight)
   {
           int cpu = bp->cpu;
           struct task_struct *tsk = bp->ctx->task;
   
           /* Pinned counter cpu profiling */
           if (!tsk) {
   
                   if (enable)
                           per_cpu(nr_cpu_bp_pinned[type], bp->cpu) += weight;
                   else
                           per_cpu(nr_cpu_bp_pinned[type], bp->cpu) -= weight;
                   return;
           }
   
           /* Pinned counter task profiling */
   
           if (!enable)
                   list_del(&bp->hw.bp_list);
   
           if (cpu >= 0) {
                   toggle_bp_task_slot(bp, cpu, enable, type, weight);
           } else {
                   for_each_online_cpu(cpu)
                           toggle_bp_task_slot(bp, cpu, enable, type, weight);
           }
   
           if (enable)
                   list_add_tail(&bp->hw.bp_list, &bp_task_head);
   }
   
   /*
    * 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
            */
   }
   
   /*
    * Contraints to check before allowing this new breakpoint counter:
    *
    *  == Non-pinned counter == (Considered as pinned for now)
    *
    *   - If attached to a single cpu, check:
    *
    *       (per_cpu(nr_bp_flexible, cpu) || (per_cpu(nr_cpu_bp_pinned, cpu)
    *           + max(per_cpu(nr_task_bp_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(nr_bp_flexible, *) || (max(per_cpu(nr_cpu_bp_pinned, *))
    *           + max(per_cpu(nr_task_bp_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(nr_bp_flexible, cpu) > 1) + per_cpu(nr_cpu_bp_pinned, cpu)
    *            + max(per_cpu(nr_task_bp_pinned, cpu))) < HBP_NUM
    *
    *       -> Same checks as before. But now the nr_bp_flexible, if any, must keep
    *          one register at least (or they will never be fed).
    *
    *   - If attached to every cpus, check:
    *
    *       ((per_cpu(nr_bp_flexible, *) > 1) + max(per_cpu(nr_cpu_bp_pinned, *))
    *            + max(per_cpu(nr_task_bp_pinned, *))) < HBP_NUM
    */
   static int __reserve_bp_slot(struct perf_event *bp)
   {
           struct bp_busy_slots slots = {0};
           enum bp_type_idx type;
           int weight;
   
           /* We couldn't initialize breakpoint constraints on boot */
           if (!constraints_initialized)
                   return -ENOMEM;
   
           /* Basic checks */
           if (bp->attr.bp_type == HW_BREAKPOINT_EMPTY ||
               bp->attr.bp_type == HW_BREAKPOINT_INVALID)
                   return -EINVAL;
   
           type = find_slot_idx(bp);
           weight = hw_breakpoint_weight(bp);
   
           fetch_bp_busy_slots(&slots, bp, type);
           /*
            * Simulate the addition of this breakpoint to the constraints
            * and see the result.
            */
           fetch_this_slot(&slots, weight);
   
           /* Flexible counters need to keep at least one slot */
           if (slots.pinned + (!!slots.flexible) > nr_slots[type])
                   return -ENOSPC;
   
           toggle_bp_slot(bp, true, type, weight);
   
           return 0;
   }
   
   int reserve_bp_slot(struct perf_event *bp)
   {
           int ret;
   
           mutex_lock(&nr_bp_mutex);
   
           ret = __reserve_bp_slot(bp);
   
           mutex_unlock(&nr_bp_mutex);
   
           return ret;
   }
   
   static void __release_bp_slot(struct perf_event *bp)
   {
           enum bp_type_idx type;
           int weight;
   
           type = find_slot_idx(bp);
           weight = hw_breakpoint_weight(bp);
           toggle_bp_slot(bp, false, type, weight);
   }
   
   void release_bp_slot(struct perf_event *bp)
   {
           mutex_lock(&nr_bp_mutex);
   
           arch_unregister_hw_breakpoint(bp);
           __release_bp_slot(bp);
   
           mutex_unlock(&nr_bp_mutex);
   }
   
   /*
    * 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)
   {
           if (mutex_is_locked(&nr_bp_mutex))
                   return -1;
   
           return __reserve_bp_slot(bp);
   }
   
   int dbg_release_bp_slot(struct perf_event *bp)
   {
           if (mutex_is_locked(&nr_bp_mutex))
                   return -1;
   
           __release_bp_slot(bp);
   
           return 0;
   }
   
   static int validate_hw_breakpoint(struct perf_event *bp)
   {
           int ret;
   
           ret = arch_validate_hwbkpt_settings(bp);
           if (ret)
                   return ret;
   
           if (arch_check_bp_in_kernelspace(bp)) {
                   if (bp->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)
   {
           int ret;
   
           ret = reserve_bp_slot(bp);
           if (ret)
                   return ret;
   
           ret = validate_hw_breakpoint(bp);
   
           /* if arch_validate_hwbkpt_settings() fails then release bp slot */
           if (ret)
                   release_bp_slot(bp);
   
           return ret;
   }
   
   /**
    * register_user_hw_breakpoint - register a hardware breakpoint for user space
    * @attr: breakpoint attributes
    * @triggered: callback to trigger when we hit the breakpoint
    * @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,
                               struct task_struct *tsk)
   {
           return perf_event_create_kernel_counter(attr, -1, tsk->pid, triggered);
   }
   EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
   
   /**
    * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
    * @bp: the breakpoint structure to modify
    * @attr: new breakpoint attributes
    * @triggered: callback to trigger when we hit the breakpoint
    * @tsk: pointer to 'task_struct' of the process to which the address belongs
    */
   int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
   {
           u64 old_addr = bp->attr.bp_addr;
           u64 old_len = bp->attr.bp_len;
           int old_type = bp->attr.bp_type;
           int err = 0;
   
           perf_event_disable(bp);
   
           bp->attr.bp_addr = attr->bp_addr;
           bp->attr.bp_type = attr->bp_type;
           bp->attr.bp_len = attr->bp_len;
   
           if (attr->disabled)
                   goto end;
   
           err = validate_hw_breakpoint(bp);
           if (!err)
                   perf_event_enable(bp);
   
           if (err) {
                   bp->attr.bp_addr = old_addr;
                   bp->attr.bp_type = old_type;
                   bp->attr.bp_len = old_len;
                   if (!bp->attr.disabled)
                           perf_event_enable(bp);
   
                   return err;
           }
   
   end:
           bp->attr.disabled = attr->disabled;
   
           return 0;
   }
   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
    *
    * @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)
   {
           struct perf_event * __percpu *cpu_events, **pevent, *bp;
           long err;
           int cpu;
   
           cpu_events = alloc_percpu(typeof(*cpu_events));
           if (!cpu_events)
                   return (void __percpu __force *)ERR_PTR(-ENOMEM);
   
           get_online_cpus();
           for_each_online_cpu(cpu) {
                   pevent = per_cpu_ptr(cpu_events, cpu);
                   bp = perf_event_create_kernel_counter(attr, cpu, -1, triggered);
   
                   *pevent = bp;
   
                   if (IS_ERR(bp)) {
                           err = PTR_ERR(bp);
                           goto fail;
                   }
           }
           put_online_cpus();
   
           return cpu_events;
   
   fail:
           for_each_online_cpu(cpu) {
                   pevent = per_cpu_ptr(cpu_events, cpu);
                   if (IS_ERR(*pevent))
                           break;
                   unregister_hw_breakpoint(*pevent);
           }
           put_online_cpus();
   
           free_percpu(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;
           struct perf_event **pevent;
   
           for_each_possible_cpu(cpu) {
                   pevent = per_cpu_ptr(cpu_events, cpu);
                   unregister_hw_breakpoint(*pevent);
           }
           free_percpu(cpu_events);
   }
   EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
   
   static struct notifier_block hw_breakpoint_exceptions_nb = {
           .notifier_call = hw_breakpoint_exceptions_notify,
           /* we need to be notified first */
           .priority = 0x7fffffff
   };
   
   static int __init init_hw_breakpoint(void)
   {
           unsigned int **task_bp_pinned;
           int cpu, err_cpu;
           int i;
   
           for (i = 0; i < TYPE_MAX; i++)
                   nr_slots[i] = hw_breakpoint_slots(i);
   
           for_each_possible_cpu(cpu) {
                   for (i = 0; i < TYPE_MAX; i++) {
                           task_bp_pinned = &per_cpu(nr_task_bp_pinned[i], cpu);
                           *task_bp_pinned = kzalloc(sizeof(int) * nr_slots[i],
                                                     GFP_KERNEL);
                           if (!*task_bp_pinned)
                                   goto err_alloc;
                   }
           }
   
           constraints_initialized = 1;
   
           return register_die_notifier(&hw_breakpoint_exceptions_nb);
   
    err_alloc:
           for_each_possible_cpu(err_cpu) {
                   if (err_cpu == cpu)
                           break;
                   for (i = 0; i < TYPE_MAX; i++)
                           kfree(per_cpu(nr_task_bp_pinned[i], cpu));
           }
   
           return -ENOMEM;
   }
   core_initcall(init_hw_breakpoint);
   
   
   struct pmu perf_ops_bp = {
           .enable         = arch_install_hw_breakpoint,
           .disable        = arch_uninstall_hw_breakpoint,
           .read           = hw_breakpoint_pmu_read,
   };

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