kernel/hw_breakpoint.c - kernel/msm-4.9 - Gitiles

 /*
  * 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,
 };
	/*
	* 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,
	};