arch/x86/kernel/hw_breakpoint.c - maze/linux - Git at Google

 /*
  * 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) 2009 IBM Corporation
  * Copyright (C) 2009 Frederic Weisbecker <fweisbec@gmail.com>
  *
  * 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.
  */

 #include <linux/perf_event.h>
 #include <linux/hw_breakpoint.h>
 #include <linux/irqflags.h>
 #include <linux/notifier.h>
 #include <linux/kallsyms.h>
 #include <linux/kprobes.h>
 #include <linux/percpu.h>
 #include <linux/kdebug.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/init.h>
 #include <linux/smp.h>

 #include <asm/hw_breakpoint.h>
 #include <asm/processor.h>
 #include <asm/debugreg.h>

 /* Per cpu debug control register value */
 DEFINE_PER_CPU(unsigned long, cpu_dr7);
 EXPORT_PER_CPU_SYMBOL(cpu_dr7);

 /* Per cpu debug address registers values */
 static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]);

 /*
  * Stores the breakpoints currently in use on each breakpoint address
  * register for each cpus
  */
 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);


 static inline unsigned long
 __encode_dr7(int drnum, unsigned int len, unsigned int type)
 {
 	unsigned long bp_info;

 	bp_info = (len | type) & 0xf;
 	bp_info <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
 	bp_info |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE));

 	return bp_info;
 }

 /*
  * Encode the length, type, Exact, and Enable bits for a particular breakpoint
  * as stored in debug register 7.
  */
 unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
 {
 	return __encode_dr7(drnum, len, type) | DR_GLOBAL_SLOWDOWN;
 }

 /*
  * Decode the length and type bits for a particular breakpoint as
  * stored in debug register 7.  Return the "enabled" status.
  */
 int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type)
 {
 	int bp_info = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);

 	*len = (bp_info & 0xc) | 0x40;
 	*type = (bp_info & 0x3) | 0x80;

 	return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
 }

 /*
  * Install a perf counter breakpoint.
  *
  * We seek a free debug address register and use it for this
  * breakpoint. Eventually we enable it in the debug control register.
  *
  * Atomic: we hold the counter->ctx->lock and we only handle variables
  * and registers local to this cpu.
  */
 int arch_install_hw_breakpoint(struct perf_event *bp)
 {
 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 	unsigned long *dr7;
 	int i;

 	for (i = 0; i < HBP_NUM; i++) {
 		struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);

 		if (!*slot) {
 			*slot = bp;
 			break;
 		}
 	}

 	if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
 		return -EBUSY;

 	set_debugreg(info->address, i);
 	__get_cpu_var(cpu_debugreg[i]) = info->address;

 	dr7 = &__get_cpu_var(cpu_dr7);
 	*dr7 |= encode_dr7(i, info->len, info->type);

 	set_debugreg(*dr7, 7);

 	return 0;
 }

 /*
  * Uninstall the breakpoint contained in the given counter.
  *
  * First we search the debug address register it uses and then we disable
  * it.
  *
  * Atomic: we hold the counter->ctx->lock and we only handle variables
  * and registers local to this cpu.
  */
 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
 {
 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 	unsigned long *dr7;
 	int i;

 	for (i = 0; i < HBP_NUM; i++) {
 		struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);

 		if (*slot == bp) {
 			*slot = NULL;
 			break;
 		}
 	}

 	if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
 		return;

 	dr7 = &__get_cpu_var(cpu_dr7);
 	*dr7 &= ~__encode_dr7(i, info->len, info->type);

 	set_debugreg(*dr7, 7);
 }

 static int get_hbp_len(u8 hbp_len)
 {
 	unsigned int len_in_bytes = 0;

 	switch (hbp_len) {
 	case X86_BREAKPOINT_LEN_1:
 		len_in_bytes = 1;
 		break;
 	case X86_BREAKPOINT_LEN_2:
 		len_in_bytes = 2;
 		break;
 	case X86_BREAKPOINT_LEN_4:
 		len_in_bytes = 4;
 		break;
 #ifdef CONFIG_X86_64
 	case X86_BREAKPOINT_LEN_8:
 		len_in_bytes = 8;
 		break;
 #endif
 	}
 	return len_in_bytes;
 }

 /*
  * Check for virtual address in kernel space.
  */
 int arch_check_bp_in_kernelspace(struct perf_event *bp)
 {
 	unsigned int len;
 	unsigned long va;
 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);

 	va = info->address;
 	len = get_hbp_len(info->len);

 	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
 }

 int arch_bp_generic_fields(int x86_len, int x86_type,
 			   int *gen_len, int *gen_type)
 {
 	/* Type */
 	switch (x86_type) {
 	case X86_BREAKPOINT_EXECUTE:
 		if (x86_len != X86_BREAKPOINT_LEN_X)
 			return -EINVAL;

 		*gen_type = HW_BREAKPOINT_X;
 		*gen_len = sizeof(long);
 		return 0;
 	case X86_BREAKPOINT_WRITE:
 		*gen_type = HW_BREAKPOINT_W;
 		break;
 	case X86_BREAKPOINT_RW:
 		*gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
 		break;
 	default:
 		return -EINVAL;
 	}

 	/* Len */
 	switch (x86_len) {
 	case X86_BREAKPOINT_LEN_1:
 		*gen_len = HW_BREAKPOINT_LEN_1;
 		break;
 	case X86_BREAKPOINT_LEN_2:
 		*gen_len = HW_BREAKPOINT_LEN_2;
 		break;
 	case X86_BREAKPOINT_LEN_4:
 		*gen_len = HW_BREAKPOINT_LEN_4;
 		break;
 #ifdef CONFIG_X86_64
 	case X86_BREAKPOINT_LEN_8:
 		*gen_len = HW_BREAKPOINT_LEN_8;
 		break;
 #endif
 	default:
 		return -EINVAL;
 	}

 	return 0;
 }


 static int arch_build_bp_info(struct perf_event *bp)
 {
 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);

 	info->address = bp->attr.bp_addr;

 	/* Type */
 	switch (bp->attr.bp_type) {
 	case HW_BREAKPOINT_W:
 		info->type = X86_BREAKPOINT_WRITE;
 		break;
 	case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
 		info->type = X86_BREAKPOINT_RW;
 		break;
 	case HW_BREAKPOINT_X:
 		info->type = X86_BREAKPOINT_EXECUTE;
 		/*
 		 * x86 inst breakpoints need to have a specific undefined len.
 		 * But we still need to check userspace is not trying to setup
 		 * an unsupported length, to get a range breakpoint for example.
 		 */
 		if (bp->attr.bp_len == sizeof(long)) {
 			info->len = X86_BREAKPOINT_LEN_X;
 			return 0;
 		}
 	default:
 		return -EINVAL;
 	}

 	/* Len */
 	switch (bp->attr.bp_len) {
 	case HW_BREAKPOINT_LEN_1:
 		info->len = X86_BREAKPOINT_LEN_1;
 		break;
 	case HW_BREAKPOINT_LEN_2:
 		info->len = X86_BREAKPOINT_LEN_2;
 		break;
 	case HW_BREAKPOINT_LEN_4:
 		info->len = X86_BREAKPOINT_LEN_4;
 		break;
 #ifdef CONFIG_X86_64
 	case HW_BREAKPOINT_LEN_8:
 		info->len = X86_BREAKPOINT_LEN_8;
 		break;
 #endif
 	default:
 		return -EINVAL;
 	}

 	return 0;
 }
 /*
  * Validate the arch-specific HW Breakpoint register settings
  */
 int arch_validate_hwbkpt_settings(struct perf_event *bp)
 {
 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 	unsigned int align;
 	int ret;


 	ret = arch_build_bp_info(bp);
 	if (ret)
 		return ret;

 	ret = -EINVAL;

 	switch (info->len) {
 	case X86_BREAKPOINT_LEN_1:
 		align = 0;
 		break;
 	case X86_BREAKPOINT_LEN_2:
 		align = 1;
 		break;
 	case X86_BREAKPOINT_LEN_4:
 		align = 3;
 		break;
 #ifdef CONFIG_X86_64
 	case X86_BREAKPOINT_LEN_8:
 		align = 7;
 		break;
 #endif
 	default:
 		return ret;
 	}

 	/*
 	 * Check that the low-order bits of the address are appropriate
 	 * for the alignment implied by len.
 	 */
 	if (info->address & align)
 		return -EINVAL;

 	return 0;
 }

 /*
  * Dump the debug register contents to the user.
  * We can't dump our per cpu values because it
  * may contain cpu wide breakpoint, something that
  * doesn't belong to the current task.
  *
  * TODO: include non-ptrace user breakpoints (perf)
  */
 void aout_dump_debugregs(struct user *dump)
 {
 	int i;
 	int dr7 = 0;
 	struct perf_event *bp;
 	struct arch_hw_breakpoint *info;
 	struct thread_struct *thread = &current->thread;

 	for (i = 0; i < HBP_NUM; i++) {
 		bp = thread->ptrace_bps[i];

 		if (bp && !bp->attr.disabled) {
 			dump->u_debugreg[i] = bp->attr.bp_addr;
 			info = counter_arch_bp(bp);
 			dr7 |= encode_dr7(i, info->len, info->type);
 		} else {
 			dump->u_debugreg[i] = 0;
 		}
 	}

 	dump->u_debugreg[4] = 0;
 	dump->u_debugreg[5] = 0;
 	dump->u_debugreg[6] = current->thread.debugreg6;

 	dump->u_debugreg[7] = dr7;
 }
 EXPORT_SYMBOL_GPL(aout_dump_debugregs);

 /*
  * Release the user breakpoints used by ptrace
  */
 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 {
 	int i;
 	struct thread_struct *t = &tsk->thread;

 	for (i = 0; i < HBP_NUM; i++) {
 		unregister_hw_breakpoint(t->ptrace_bps[i]);
 		t->ptrace_bps[i] = NULL;
 	}
 }

 void hw_breakpoint_restore(void)
 {
 	set_debugreg(__get_cpu_var(cpu_debugreg[0]), 0);
 	set_debugreg(__get_cpu_var(cpu_debugreg[1]), 1);
 	set_debugreg(__get_cpu_var(cpu_debugreg[2]), 2);
 	set_debugreg(__get_cpu_var(cpu_debugreg[3]), 3);
 	set_debugreg(current->thread.debugreg6, 6);
 	set_debugreg(__get_cpu_var(cpu_dr7), 7);
 }
 EXPORT_SYMBOL_GPL(hw_breakpoint_restore);

 /*
  * Handle debug exception notifications.
  *
  * Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
  *
  * NOTIFY_DONE returned if one of the following conditions is true.
  * i) When the causative address is from user-space and the exception
  * is a valid one, i.e. not triggered as a result of lazy debug register
  * switching
  * ii) When there are more bits than trap<n> set in DR6 register (such
  * as BD, BS or BT) indicating that more than one debug condition is
  * met and requires some more action in do_debug().
  *
  * NOTIFY_STOP returned for all other cases
  *
  */
 static int __kprobes hw_breakpoint_handler(struct die_args *args)
 {
 	int i, cpu, rc = NOTIFY_STOP;
 	struct perf_event *bp;
 	unsigned long dr7, dr6;
 	unsigned long *dr6_p;

 	/* The DR6 value is pointed by args->err */
 	dr6_p = (unsigned long *)ERR_PTR(args->err);
 	dr6 = *dr6_p;

 	/* If it's a single step, TRAP bits are random */
 	if (dr6 & DR_STEP)
 		return NOTIFY_DONE;

 	/* Do an early return if no trap bits are set in DR6 */
 	if ((dr6 & DR_TRAP_BITS) == 0)
 		return NOTIFY_DONE;

 	get_debugreg(dr7, 7);
 	/* Disable breakpoints during exception handling */
 	set_debugreg(0UL, 7);
 	/*
 	 * Assert that local interrupts are disabled
 	 * Reset the DRn bits in the virtualized register value.
 	 * The ptrace trigger routine will add in whatever is needed.
 	 */
 	current->thread.debugreg6 &= ~DR_TRAP_BITS;
 	cpu = get_cpu();

 	/* Handle all the breakpoints that were triggered */
 	for (i = 0; i < HBP_NUM; ++i) {
 		if (likely(!(dr6 & (DR_TRAP0 << i))))
 			continue;

 		/*
 		 * The counter may be concurrently released but that can only
 		 * occur from a call_rcu() path. We can then safely fetch
 		 * the breakpoint, use its callback, touch its counter
 		 * while we are in an rcu_read_lock() path.
 		 */
 		rcu_read_lock();

 		bp = per_cpu(bp_per_reg[i], cpu);
 		/*
 		 * Reset the 'i'th TRAP bit in dr6 to denote completion of
 		 * exception handling
 		 */
 		(*dr6_p) &= ~(DR_TRAP0 << i);
 		/*
 		 * bp can be NULL due to lazy debug register switching
 		 * or due to concurrent perf counter removing.
 		 */
 		if (!bp) {
 			rcu_read_unlock();
 			break;
 		}

 		perf_bp_event(bp, args->regs);

 		/*
 		 * Set up resume flag to avoid breakpoint recursion when
 		 * returning back to origin.
 		 */
 		if (bp->hw.info.type == X86_BREAKPOINT_EXECUTE)
 			args->regs->flags |= X86_EFLAGS_RF;

 		rcu_read_unlock();
 	}
 	/*
 	 * Further processing in do_debug() is needed for a) user-space
 	 * breakpoints (to generate signals) and b) when the system has
 	 * taken exception due to multiple causes
 	 */
 	if ((current->thread.debugreg6 & DR_TRAP_BITS) ||
 	    (dr6 & (~DR_TRAP_BITS)))
 		rc = NOTIFY_DONE;

 	set_debugreg(dr7, 7);
 	put_cpu();

 	return rc;
 }

 /*
  * Handle debug exception notifications.
  */
 int __kprobes hw_breakpoint_exceptions_notify(
 		struct notifier_block *unused, unsigned long val, void *data)
 {
 	if (val != DIE_DEBUG)
 		return NOTIFY_DONE;

 	return hw_breakpoint_handler(data);
 }

 void hw_breakpoint_pmu_read(struct perf_event *bp)
 {
 	/* TODO */
 }
	/*
	* 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) 2009 IBM Corporation
	* Copyright (C) 2009 Frederic Weisbecker <fweisbec@gmail.com>
	*
	* 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.
	*/

	#include <linux/perf_event.h>
	#include <linux/hw_breakpoint.h>
	#include <linux/irqflags.h>
	#include <linux/notifier.h>
	#include <linux/kallsyms.h>
	#include <linux/kprobes.h>
	#include <linux/percpu.h>
	#include <linux/kdebug.h>
	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/sched.h>
	#include <linux/init.h>
	#include <linux/smp.h>

	#include <asm/hw_breakpoint.h>
	#include <asm/processor.h>
	#include <asm/debugreg.h>

	/* Per cpu debug control register value */
	DEFINE_PER_CPU(unsigned long, cpu_dr7);
	EXPORT_PER_CPU_SYMBOL(cpu_dr7);

	/* Per cpu debug address registers values */
	static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]);

	/*
	* Stores the breakpoints currently in use on each breakpoint address
	* register for each cpus
	*/
	static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);


	static inline unsigned long
	__encode_dr7(int drnum, unsigned int len, unsigned int type)
	{
	unsigned long bp_info;

	bp_info = (len \| type) & 0xf;
	bp_info <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
	bp_info \|= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE));

	return bp_info;
	}

	/*
	* Encode the length, type, Exact, and Enable bits for a particular breakpoint
	* as stored in debug register 7.
	*/
	unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
	{
	return __encode_dr7(drnum, len, type) \| DR_GLOBAL_SLOWDOWN;
	}

	/*
	* Decode the length and type bits for a particular breakpoint as
	* stored in debug register 7. Return the "enabled" status.
	*/
	int decode_dr7(unsigned long dr7, int bpnum, unsigned len, unsigned type)
	{
	int bp_info = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);

	*len = (bp_info & 0xc) \| 0x40;
	*type = (bp_info & 0x3) \| 0x80;

	return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
	}

	/*
	* Install a perf counter breakpoint.
	*
	* We seek a free debug address register and use it for this
	* breakpoint. Eventually we enable it in the debug control register.
	*
	* Atomic: we hold the counter->ctx->lock and we only handle variables
	* and registers local to this cpu.
	*/
	int arch_install_hw_breakpoint(struct perf_event *bp)
	{
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
	unsigned long *dr7;
	int i;

	for (i = 0; i < HBP_NUM; i++) {
	struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);

	if (!*slot) {
	*slot = bp;
	break;
	}
	}

	if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
	return -EBUSY;

	set_debugreg(info->address, i);
	__get_cpu_var(cpu_debugreg[i]) = info->address;

	dr7 = &__get_cpu_var(cpu_dr7);
	*dr7 \|= encode_dr7(i, info->len, info->type);

	set_debugreg(*dr7, 7);

	return 0;
	}

	/*
	* Uninstall the breakpoint contained in the given counter.
	*
	* First we search the debug address register it uses and then we disable
	* it.
	*
	* Atomic: we hold the counter->ctx->lock and we only handle variables
	* and registers local to this cpu.
	*/
	void arch_uninstall_hw_breakpoint(struct perf_event *bp)
	{
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
	unsigned long *dr7;
	int i;

	for (i = 0; i < HBP_NUM; i++) {
	struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);

	if (*slot == bp) {
	*slot = NULL;
	break;
	}
	}

	if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
	return;

	dr7 = &__get_cpu_var(cpu_dr7);
	*dr7 &= ~__encode_dr7(i, info->len, info->type);

	set_debugreg(*dr7, 7);
	}

	static int get_hbp_len(u8 hbp_len)
	{
	unsigned int len_in_bytes = 0;

	switch (hbp_len) {
	case X86_BREAKPOINT_LEN_1:
	len_in_bytes = 1;
	break;
	case X86_BREAKPOINT_LEN_2:
	len_in_bytes = 2;
	break;
	case X86_BREAKPOINT_LEN_4:
	len_in_bytes = 4;
	break;
	#ifdef CONFIG_X86_64
	case X86_BREAKPOINT_LEN_8:
	len_in_bytes = 8;
	break;
	#endif
	}
	return len_in_bytes;
	}

	/*
	* Check for virtual address in kernel space.
	*/
	int arch_check_bp_in_kernelspace(struct perf_event *bp)
	{
	unsigned int len;
	unsigned long va;
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);

	va = info->address;
	len = get_hbp_len(info->len);

	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
	}

	int arch_bp_generic_fields(int x86_len, int x86_type,
	int gen_len, int gen_type)
	{
	/* Type */
	switch (x86_type) {
	case X86_BREAKPOINT_EXECUTE:
	if (x86_len != X86_BREAKPOINT_LEN_X)
	return -EINVAL;

	*gen_type = HW_BREAKPOINT_X;
	*gen_len = sizeof(long);
	return 0;
	case X86_BREAKPOINT_WRITE:
	*gen_type = HW_BREAKPOINT_W;
	break;
	case X86_BREAKPOINT_RW:
	*gen_type = HW_BREAKPOINT_W \| HW_BREAKPOINT_R;
	break;
	default:
	return -EINVAL;
	}

	/* Len */
	switch (x86_len) {
	case X86_BREAKPOINT_LEN_1:
	*gen_len = HW_BREAKPOINT_LEN_1;
	break;
	case X86_BREAKPOINT_LEN_2:
	*gen_len = HW_BREAKPOINT_LEN_2;
	break;
	case X86_BREAKPOINT_LEN_4:
	*gen_len = HW_BREAKPOINT_LEN_4;
	break;
	#ifdef CONFIG_X86_64
	case X86_BREAKPOINT_LEN_8:
	*gen_len = HW_BREAKPOINT_LEN_8;
	break;
	#endif
	default:
	return -EINVAL;
	}

	return 0;
	}


	static int arch_build_bp_info(struct perf_event *bp)
	{
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);

	info->address = bp->attr.bp_addr;

	/* Type */
	switch (bp->attr.bp_type) {
	case HW_BREAKPOINT_W:
	info->type = X86_BREAKPOINT_WRITE;
	break;
	case HW_BREAKPOINT_W \| HW_BREAKPOINT_R:
	info->type = X86_BREAKPOINT_RW;
	break;
	case HW_BREAKPOINT_X:
	info->type = X86_BREAKPOINT_EXECUTE;
	/*
	* x86 inst breakpoints need to have a specific undefined len.
	* But we still need to check userspace is not trying to setup
	* an unsupported length, to get a range breakpoint for example.
	*/
	if (bp->attr.bp_len == sizeof(long)) {
	info->len = X86_BREAKPOINT_LEN_X;
	return 0;
	}
	default:
	return -EINVAL;
	}

	/* Len */
	switch (bp->attr.bp_len) {
	case HW_BREAKPOINT_LEN_1:
	info->len = X86_BREAKPOINT_LEN_1;
	break;
	case HW_BREAKPOINT_LEN_2:
	info->len = X86_BREAKPOINT_LEN_2;
	break;
	case HW_BREAKPOINT_LEN_4:
	info->len = X86_BREAKPOINT_LEN_4;
	break;
	#ifdef CONFIG_X86_64
	case HW_BREAKPOINT_LEN_8:
	info->len = X86_BREAKPOINT_LEN_8;
	break;
	#endif
	default:
	return -EINVAL;
	}

	return 0;
	}
	/*
	* Validate the arch-specific HW Breakpoint register settings
	*/
	int arch_validate_hwbkpt_settings(struct perf_event *bp)
	{
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
	unsigned int align;
	int ret;


	ret = arch_build_bp_info(bp);
	if (ret)
	return ret;

	ret = -EINVAL;

	switch (info->len) {
	case X86_BREAKPOINT_LEN_1:
	align = 0;
	break;
	case X86_BREAKPOINT_LEN_2:
	align = 1;
	break;
	case X86_BREAKPOINT_LEN_4:
	align = 3;
	break;
	#ifdef CONFIG_X86_64
	case X86_BREAKPOINT_LEN_8:
	align = 7;
	break;
	#endif
	default:
	return ret;
	}

	/*
	* Check that the low-order bits of the address are appropriate
	* for the alignment implied by len.
	*/
	if (info->address & align)
	return -EINVAL;

	return 0;
	}

	/*
	* Dump the debug register contents to the user.
	* We can't dump our per cpu values because it
	* may contain cpu wide breakpoint, something that
	* doesn't belong to the current task.
	*
	* TODO: include non-ptrace user breakpoints (perf)
	*/
	void aout_dump_debugregs(struct user *dump)
	{
	int i;
	int dr7 = 0;
	struct perf_event *bp;
	struct arch_hw_breakpoint *info;
	struct thread_struct *thread = &current->thread;

	for (i = 0; i < HBP_NUM; i++) {
	bp = thread->ptrace_bps[i];

	if (bp && !bp->attr.disabled) {
	dump->u_debugreg[i] = bp->attr.bp_addr;
	info = counter_arch_bp(bp);
	dr7 \|= encode_dr7(i, info->len, info->type);
	} else {
	dump->u_debugreg[i] = 0;
	}
	}

	dump->u_debugreg[4] = 0;
	dump->u_debugreg[5] = 0;
	dump->u_debugreg[6] = current->thread.debugreg6;

	dump->u_debugreg[7] = dr7;
	}
	EXPORT_SYMBOL_GPL(aout_dump_debugregs);

	/*
	* Release the user breakpoints used by ptrace
	*/
	void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
	{
	int i;
	struct thread_struct *t = &tsk->thread;

	for (i = 0; i < HBP_NUM; i++) {
	unregister_hw_breakpoint(t->ptrace_bps[i]);
	t->ptrace_bps[i] = NULL;
	}
	}

	void hw_breakpoint_restore(void)
	{
	set_debugreg(__get_cpu_var(cpu_debugreg[0]), 0);
	set_debugreg(__get_cpu_var(cpu_debugreg[1]), 1);
	set_debugreg(__get_cpu_var(cpu_debugreg[2]), 2);
	set_debugreg(__get_cpu_var(cpu_debugreg[3]), 3);
	set_debugreg(current->thread.debugreg6, 6);
	set_debugreg(__get_cpu_var(cpu_dr7), 7);
	}
	EXPORT_SYMBOL_GPL(hw_breakpoint_restore);

	/*
	* Handle debug exception notifications.
	*
	* Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
	*
	* NOTIFY_DONE returned if one of the following conditions is true.
	* i) When the causative address is from user-space and the exception
	* is a valid one, i.e. not triggered as a result of lazy debug register
	* switching
	* ii) When there are more bits than trap<n> set in DR6 register (such
	* as BD, BS or BT) indicating that more than one debug condition is
	* met and requires some more action in do_debug().
	*
	* NOTIFY_STOP returned for all other cases
	*
	*/
	static int __kprobes hw_breakpoint_handler(struct die_args *args)
	{
	int i, cpu, rc = NOTIFY_STOP;
	struct perf_event *bp;
	unsigned long dr7, dr6;
	unsigned long *dr6_p;

	/* The DR6 value is pointed by args->err */
	dr6_p = (unsigned long *)ERR_PTR(args->err);
	dr6 = *dr6_p;

	/* If it's a single step, TRAP bits are random */
	if (dr6 & DR_STEP)
	return NOTIFY_DONE;

	/* Do an early return if no trap bits are set in DR6 */
	if ((dr6 & DR_TRAP_BITS) == 0)
	return NOTIFY_DONE;

	get_debugreg(dr7, 7);
	/* Disable breakpoints during exception handling */
	set_debugreg(0UL, 7);
	/*
	* Assert that local interrupts are disabled
	* Reset the DRn bits in the virtualized register value.
	* The ptrace trigger routine will add in whatever is needed.
	*/
	current->thread.debugreg6 &= ~DR_TRAP_BITS;
	cpu = get_cpu();

	/* Handle all the breakpoints that were triggered */
	for (i = 0; i < HBP_NUM; ++i) {
	if (likely(!(dr6 & (DR_TRAP0 << i))))
	continue;

	/*
	* The counter may be concurrently released but that can only
	* occur from a call_rcu() path. We can then safely fetch
	* the breakpoint, use its callback, touch its counter
	* while we are in an rcu_read_lock() path.
	*/
	rcu_read_lock();

	bp = per_cpu(bp_per_reg[i], cpu);
	/*
	* Reset the 'i'th TRAP bit in dr6 to denote completion of
	* exception handling
	*/
	(*dr6_p) &= ~(DR_TRAP0 << i);
	/*
	* bp can be NULL due to lazy debug register switching
	* or due to concurrent perf counter removing.
	*/
	if (!bp) {
	rcu_read_unlock();
	break;
	}

	perf_bp_event(bp, args->regs);

	/*
	* Set up resume flag to avoid breakpoint recursion when
	* returning back to origin.
	*/
	if (bp->hw.info.type == X86_BREAKPOINT_EXECUTE)
	args->regs->flags \|= X86_EFLAGS_RF;

	rcu_read_unlock();
	}
	/*
	* Further processing in do_debug() is needed for a) user-space
	* breakpoints (to generate signals) and b) when the system has
	* taken exception due to multiple causes
	*/
	if ((current->thread.debugreg6 & DR_TRAP_BITS) \|\|
	(dr6 & (~DR_TRAP_BITS)))
	rc = NOTIFY_DONE;

	set_debugreg(dr7, 7);
	put_cpu();

	return rc;
	}

	/*
	* Handle debug exception notifications.
	*/
	int __kprobes hw_breakpoint_exceptions_notify(
	struct notifier_block unused, unsigned long val, void data)
	{
	if (val != DIE_DEBUG)
	return NOTIFY_DONE;

	return hw_breakpoint_handler(data);
	}

	void hw_breakpoint_pmu_read(struct perf_event *bp)
	{
	/* TODO */
	}