arm64: Debugging support

This patch adds ptrace, debug monitors and hardware breakpoints support.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 880 insertions, 0 deletions

diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
new file mode 100644
index 000000000000..5ab825c59db9
--- /dev/null
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -0,0 +1,880 @@
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ *
+ * Copyright (C) 2012 ARM Limited
+ * Author: Will Deacon <will.deacon@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#define pr_fmt(fmt) "hw-breakpoint: " fmt
+
+#include <linux/errno.h>
+#include <linux/hw_breakpoint.h>
+#include <linux/perf_event.h>
+#include <linux/ptrace.h>
+#include <linux/smp.h>
+
+#include <asm/compat.h>
+#include <asm/current.h>
+#include <asm/debug-monitors.h>
+#include <asm/hw_breakpoint.h>
+#include <asm/kdebug.h>
+#include <asm/traps.h>
+#include <asm/cputype.h>
+#include <asm/system_misc.h>
+
+/* Breakpoint currently in use for each BRP. */
+static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]);
+
+/* Watchpoint currently in use for each WRP. */
+static DEFINE_PER_CPU(struct perf_event *, wp_on_reg[ARM_MAX_WRP]);
+
+/* Currently stepping a per-CPU kernel breakpoint. */
+static DEFINE_PER_CPU(int, stepping_kernel_bp);
+
+/* Number of BRP/WRP registers on this CPU. */
+static int core_num_brps;
+static int core_num_wrps;
+
+/* Determine number of BRP registers available. */
+static int get_num_brps(void)
+{
+	return ((read_cpuid(ID_AA64DFR0_EL1) >> 12) & 0xf) + 1;
+}
+
+/* Determine number of WRP registers available. */
+static int get_num_wrps(void)
+{
+	return ((read_cpuid(ID_AA64DFR0_EL1) >> 20) & 0xf) + 1;
+}
+
+int hw_breakpoint_slots(int type)
+{
+	/*
+	 * We can be called early, so don't rely on
+	 * our static variables being initialised.
+	 */
+	switch (type) {
+	case TYPE_INST:
+		return get_num_brps();
+	case TYPE_DATA:
+		return get_num_wrps();
+	default:
+		pr_warning("unknown slot type: %d\n", type);
+		return 0;
+	}
+}
+
+#define READ_WB_REG_CASE(OFF, N, REG, VAL)	\
+	case (OFF + N):				\
+		AARCH64_DBG_READ(N, REG, VAL);	\
+		break
+
+#define WRITE_WB_REG_CASE(OFF, N, REG, VAL)	\
+	case (OFF + N):				\
+		AARCH64_DBG_WRITE(N, REG, VAL);	\
+		break
+
+#define GEN_READ_WB_REG_CASES(OFF, REG, VAL)	\
+	READ_WB_REG_CASE(OFF,  0, REG, VAL);	\
+	READ_WB_REG_CASE(OFF,  1, REG, VAL);	\
+	READ_WB_REG_CASE(OFF,  2, REG, VAL);	\
+	READ_WB_REG_CASE(OFF,  3, REG, VAL);	\
+	READ_WB_REG_CASE(OFF,  4, REG, VAL);	\
+	READ_WB_REG_CASE(OFF,  5, REG, VAL);	\
+	READ_WB_REG_CASE(OFF,  6, REG, VAL);	\
+	READ_WB_REG_CASE(OFF,  7, REG, VAL);	\
+	READ_WB_REG_CASE(OFF,  8, REG, VAL);	\
+	READ_WB_REG_CASE(OFF,  9, REG, VAL);	\
+	READ_WB_REG_CASE(OFF, 10, REG, VAL);	\
+	READ_WB_REG_CASE(OFF, 11, REG, VAL);	\
+	READ_WB_REG_CASE(OFF, 12, REG, VAL);	\
+	READ_WB_REG_CASE(OFF, 13, REG, VAL);	\
+	READ_WB_REG_CASE(OFF, 14, REG, VAL);	\
+	READ_WB_REG_CASE(OFF, 15, REG, VAL)
+
+#define GEN_WRITE_WB_REG_CASES(OFF, REG, VAL)	\
+	WRITE_WB_REG_CASE(OFF,  0, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF,  1, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF,  2, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF,  3, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF,  4, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF,  5, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF,  6, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF,  7, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF,  8, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF,  9, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF, 10, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF, 11, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF, 12, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF, 13, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF, 14, REG, VAL);	\
+	WRITE_WB_REG_CASE(OFF, 15, REG, VAL)
+
+static u64 read_wb_reg(int reg, int n)
+{
+	u64 val = 0;
+
+	switch (reg + n) {
+	GEN_READ_WB_REG_CASES(AARCH64_DBG_REG_BVR, AARCH64_DBG_REG_NAME_BVR, val);
+	GEN_READ_WB_REG_CASES(AARCH64_DBG_REG_BCR, AARCH64_DBG_REG_NAME_BCR, val);
+	GEN_READ_WB_REG_CASES(AARCH64_DBG_REG_WVR, AARCH64_DBG_REG_NAME_WVR, val);
+	GEN_READ_WB_REG_CASES(AARCH64_DBG_REG_WCR, AARCH64_DBG_REG_NAME_WCR, val);
+	default:
+		pr_warning("attempt to read from unknown breakpoint register %d\n", n);
+	}
+
+	return val;
+}
+
+static void write_wb_reg(int reg, int n, u64 val)
+{
+	switch (reg + n) {
+	GEN_WRITE_WB_REG_CASES(AARCH64_DBG_REG_BVR, AARCH64_DBG_REG_NAME_BVR, val);
+	GEN_WRITE_WB_REG_CASES(AARCH64_DBG_REG_BCR, AARCH64_DBG_REG_NAME_BCR, val);
+	GEN_WRITE_WB_REG_CASES(AARCH64_DBG_REG_WVR, AARCH64_DBG_REG_NAME_WVR, val);
+	GEN_WRITE_WB_REG_CASES(AARCH64_DBG_REG_WCR, AARCH64_DBG_REG_NAME_WCR, val);
+	default:
+		pr_warning("attempt to write to unknown breakpoint register %d\n", n);
+	}
+	isb();
+}
+
+/*
+ * Convert a breakpoint privilege level to the corresponding exception
+ * level.
+ */
+static enum debug_el debug_exception_level(int privilege)
+{
+	switch (privilege) {
+	case AARCH64_BREAKPOINT_EL0:
+		return DBG_ACTIVE_EL0;
+	case AARCH64_BREAKPOINT_EL1:
+		return DBG_ACTIVE_EL1;
+	default:
+		pr_warning("invalid breakpoint privilege level %d\n", privilege);
+		return -EINVAL;
+	}
+}
+
+/*
+ * Install a perf counter breakpoint.
+ */
+int arch_install_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	struct debug_info *debug_info = &current->thread.debug;
+	int i, max_slots, ctrl_reg, val_reg, reg_enable;
+	u32 ctrl;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		ctrl_reg = AARCH64_DBG_REG_BCR;
+		val_reg = AARCH64_DBG_REG_BVR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps;
+		reg_enable = !debug_info->bps_disabled;
+	} else {
+		/* Watchpoint */
+		ctrl_reg = AARCH64_DBG_REG_WCR;
+		val_reg = AARCH64_DBG_REG_WVR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+		reg_enable = !debug_info->wps_disabled;
+	}
+
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (!*slot) {
+			*slot = bp;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot"))
+		return -ENOSPC;
+
+	/* Ensure debug monitors are enabled at the correct exception level.  */
+	enable_debug_monitors(debug_exception_level(info->ctrl.privilege));
+
+	/* Setup the address register. */
+	write_wb_reg(val_reg, i, info->address);
+
+	/* Setup the control register. */
+	ctrl = encode_ctrl_reg(info->ctrl);
+	write_wb_reg(ctrl_reg, i, reg_enable ? ctrl | 0x1 : ctrl & ~0x1);
+
+	return 0;
+}
+
+void arch_uninstall_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot, **slots;
+	int i, max_slots, base;
+
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		/* Breakpoint */
+		base = AARCH64_DBG_REG_BCR;
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps;
+	} else {
+		/* Watchpoint */
+		base = AARCH64_DBG_REG_WCR;
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+	}
+
+	/* Remove the breakpoint. */
+	for (i = 0; i < max_slots; ++i) {
+		slot = &slots[i];
+
+		if (*slot == bp) {
+			*slot = NULL;
+			break;
+		}
+	}
+
+	if (WARN_ONCE(i == max_slots, "Can't find any breakpoint slot"))
+		return;
+
+	/* Reset the control register. */
+	write_wb_reg(base, i, 0);
+
+	/* Release the debug monitors for the correct exception level.  */
+	disable_debug_monitors(debug_exception_level(info->ctrl.privilege));
+}
+
+static int get_hbp_len(u8 hbp_len)
+{
+	unsigned int len_in_bytes = 0;
+
+	switch (hbp_len) {
+	case ARM_BREAKPOINT_LEN_1:
+		len_in_bytes = 1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		len_in_bytes = 2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		len_in_bytes = 4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		len_in_bytes = 8;
+		break;
+	}
+
+	return len_in_bytes;
+}
+
+/*
+ * Check whether bp virtual address is 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->ctrl.len);
+
+	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
+}
+
+/*
+ * Extract generic type and length encodings from an arch_hw_breakpoint_ctrl.
+ * Hopefully this will disappear when ptrace can bypass the conversion
+ * to generic breakpoint descriptions.
+ */
+int arch_bp_generic_fields(struct arch_hw_breakpoint_ctrl ctrl,
+			   int *gen_len, int *gen_type)
+{
+	/* Type */
+	switch (ctrl.type) {
+	case ARM_BREAKPOINT_EXECUTE:
+		*gen_type = HW_BREAKPOINT_X;
+		break;
+	case ARM_BREAKPOINT_LOAD:
+		*gen_type = HW_BREAKPOINT_R;
+		break;
+	case ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_W;
+		break;
+	case ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE:
+		*gen_type = HW_BREAKPOINT_RW;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (ctrl.len) {
+	case ARM_BREAKPOINT_LEN_1:
+		*gen_len = HW_BREAKPOINT_LEN_1;
+		break;
+	case ARM_BREAKPOINT_LEN_2:
+		*gen_len = HW_BREAKPOINT_LEN_2;
+		break;
+	case ARM_BREAKPOINT_LEN_4:
+		*gen_len = HW_BREAKPOINT_LEN_4;
+		break;
+	case ARM_BREAKPOINT_LEN_8:
+		*gen_len = HW_BREAKPOINT_LEN_8;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/*
+ * Construct an arch_hw_breakpoint from a perf_event.
+ */
+static int arch_build_bp_info(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	/* Type */
+	switch (bp->attr.bp_type) {
+	case HW_BREAKPOINT_X:
+		info->ctrl.type = ARM_BREAKPOINT_EXECUTE;
+		break;
+	case HW_BREAKPOINT_R:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD;
+		break;
+	case HW_BREAKPOINT_W:
+		info->ctrl.type = ARM_BREAKPOINT_STORE;
+		break;
+	case HW_BREAKPOINT_RW:
+		info->ctrl.type = ARM_BREAKPOINT_LOAD | ARM_BREAKPOINT_STORE;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Len */
+	switch (bp->attr.bp_len) {
+	case HW_BREAKPOINT_LEN_1:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_1;
+		break;
+	case HW_BREAKPOINT_LEN_2:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_2;
+		break;
+	case HW_BREAKPOINT_LEN_4:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_4;
+		break;
+	case HW_BREAKPOINT_LEN_8:
+		info->ctrl.len = ARM_BREAKPOINT_LEN_8;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/*
+	 * On AArch64, we only permit breakpoints of length 4, whereas
+	 * AArch32 also requires breakpoints of length 2 for Thumb.
+	 * Watchpoints can be of length 1, 2, 4 or 8 bytes.
+	 */
+	if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
+		if (is_compat_task()) {
+			if (info->ctrl.len != ARM_BREAKPOINT_LEN_2 &&
+			    info->ctrl.len != ARM_BREAKPOINT_LEN_4)
+				return -EINVAL;
+		} else if (info->ctrl.len != ARM_BREAKPOINT_LEN_4) {
+			/*
+			 * FIXME: Some tools (I'm looking at you perf) assume
+			 *	  that breakpoints should be sizeof(long). This
+			 *	  is nonsense. For now, we fix up the parameter
+			 *	  but we should probably return -EINVAL instead.
+			 */
+			info->ctrl.len = ARM_BREAKPOINT_LEN_4;
+		}
+	}
+
+	/* Address */
+	info->address = bp->attr.bp_addr;
+
+	/*
+	 * Privilege
+	 * Note that we disallow combined EL0/EL1 breakpoints because
+	 * that would complicate the stepping code.
+	 */
+	if (arch_check_bp_in_kernelspace(bp))
+		info->ctrl.privilege = AARCH64_BREAKPOINT_EL1;
+	else
+		info->ctrl.privilege = AARCH64_BREAKPOINT_EL0;
+
+	/* Enabled? */
+	info->ctrl.enabled = !bp->attr.disabled;
+
+	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);
+	int ret;
+	u64 alignment_mask, offset;
+
+	/* Build the arch_hw_breakpoint. */
+	ret = arch_build_bp_info(bp);
+	if (ret)
+		return ret;
+
+	/*
+	 * Check address alignment.
+	 * We don't do any clever alignment correction for watchpoints
+	 * because using 64-bit unaligned addresses is deprecated for
+	 * AArch64.
+	 *
+	 * AArch32 tasks expect some simple alignment fixups, so emulate
+	 * that here.
+	 */
+	if (is_compat_task()) {
+		if (info->ctrl.len == ARM_BREAKPOINT_LEN_8)
+			alignment_mask = 0x7;
+		else
+			alignment_mask = 0x3;
+		offset = info->address & alignment_mask;
+		switch (offset) {
+		case 0:
+			/* Aligned */
+			break;
+		case 1:
+			/* Allow single byte watchpoint. */
+			if (info->ctrl.len == ARM_BREAKPOINT_LEN_1)
+				break;
+		case 2:
+			/* Allow halfword watchpoints and breakpoints. */
+			if (info->ctrl.len == ARM_BREAKPOINT_LEN_2)
+				break;
+		default:
+			return -EINVAL;
+		}
+
+		info->address &= ~alignment_mask;
+		info->ctrl.len <<= offset;
+	} else {
+		if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE)
+			alignment_mask = 0x3;
+		else
+			alignment_mask = 0x7;
+		if (info->address & alignment_mask)
+			return -EINVAL;
+	}
+
+	/*
+	 * Disallow per-task kernel breakpoints since these would
+	 * complicate the stepping code.
+	 */
+	if (info->ctrl.privilege == AARCH64_BREAKPOINT_EL1 && bp->hw.bp_target)
+		return -EINVAL;
+
+	return 0;
+}
+
+/*
+ * Enable/disable all of the breakpoints active at the specified
+ * exception level at the register level.
+ * This is used when single-stepping after a breakpoint exception.
+ */
+static void toggle_bp_registers(int reg, enum debug_el el, int enable)
+{
+	int i, max_slots, privilege;
+	u32 ctrl;
+	struct perf_event **slots;
+
+	switch (reg) {
+	case AARCH64_DBG_REG_BCR:
+		slots = __get_cpu_var(bp_on_reg);
+		max_slots = core_num_brps;
+		break;
+	case AARCH64_DBG_REG_WCR:
+		slots = __get_cpu_var(wp_on_reg);
+		max_slots = core_num_wrps;
+		break;
+	default:
+		return;
+	}
+
+	for (i = 0; i < max_slots; ++i) {
+		if (!slots[i])
+			continue;
+
+		privilege = counter_arch_bp(slots[i])->ctrl.privilege;
+		if (debug_exception_level(privilege) != el)
+			continue;
+
+		ctrl = read_wb_reg(reg, i);
+		if (enable)
+			ctrl |= 0x1;
+		else
+			ctrl &= ~0x1;
+		write_wb_reg(reg, i, ctrl);
+	}
+}
+
+/*
+ * Debug exception handlers.
+ */
+static int breakpoint_handler(unsigned long unused, unsigned int esr,
+			      struct pt_regs *regs)
+{
+	int i, step = 0, *kernel_step;
+	u32 ctrl_reg;
+	u64 addr, val;
+	struct perf_event *bp, **slots;
+	struct debug_info *debug_info;
+	struct arch_hw_breakpoint_ctrl ctrl;
+
+	slots = (struct perf_event **)__get_cpu_var(bp_on_reg);
+	addr = instruction_pointer(regs);
+	debug_info = &current->thread.debug;
+
+	for (i = 0; i < core_num_brps; ++i) {
+		rcu_read_lock();
+
+		bp = slots[i];
+
+		if (bp == NULL)
+			goto unlock;
+
+		/* Check if the breakpoint value matches. */
+		val = read_wb_reg(AARCH64_DBG_REG_BVR, i);
+		if (val != (addr & ~0x3))
+			goto unlock;
+
+		/* Possible match, check the byte address select to confirm. */
+		ctrl_reg = read_wb_reg(AARCH64_DBG_REG_BCR, i);
+		decode_ctrl_reg(ctrl_reg, &ctrl);
+		if (!((1 << (addr & 0x3)) & ctrl.len))
+			goto unlock;
+
+		counter_arch_bp(bp)->trigger = addr;
+		perf_bp_event(bp, regs);
+
+		/* Do we need to handle the stepping? */
+		if (!bp->overflow_handler)
+			step = 1;
+unlock:
+		rcu_read_unlock();
+	}
+
+	if (!step)
+		return 0;
+
+	if (user_mode(regs)) {
+		debug_info->bps_disabled = 1;
+		toggle_bp_registers(AARCH64_DBG_REG_BCR, DBG_ACTIVE_EL0, 0);
+
+		/* If we're already stepping a watchpoint, just return. */
+		if (debug_info->wps_disabled)
+			return 0;
+
+		if (test_thread_flag(TIF_SINGLESTEP))
+			debug_info->suspended_step = 1;
+		else
+			user_enable_single_step(current);
+	} else {
+		toggle_bp_registers(AARCH64_DBG_REG_BCR, DBG_ACTIVE_EL1, 0);
+		kernel_step = &__get_cpu_var(stepping_kernel_bp);
+
+		if (*kernel_step != ARM_KERNEL_STEP_NONE)
+			return 0;
+
+		if (kernel_active_single_step()) {
+			*kernel_step = ARM_KERNEL_STEP_SUSPEND;
+		} else {
+			*kernel_step = ARM_KERNEL_STEP_ACTIVE;
+			kernel_enable_single_step(regs);
+		}
+	}
+
+	return 0;
+}
+
+static int watchpoint_handler(unsigned long addr, unsigned int esr,
+			      struct pt_regs *regs)
+{
+	int i, step = 0, *kernel_step, access;
+	u32 ctrl_reg;
+	u64 val, alignment_mask;
+	struct perf_event *wp, **slots;
+	struct debug_info *debug_info;
+	struct arch_hw_breakpoint *info;
+	struct arch_hw_breakpoint_ctrl ctrl;
+
+	slots = (struct perf_event **)__get_cpu_var(wp_on_reg);
+	debug_info = &current->thread.debug;
+
+	for (i = 0; i < core_num_wrps; ++i) {
+		rcu_read_lock();
+
+		wp = slots[i];
+
+		if (wp == NULL)
+			goto unlock;
+
+		info = counter_arch_bp(wp);
+		/* AArch32 watchpoints are either 4 or 8 bytes aligned. */
+		if (is_compat_task()) {
+			if (info->ctrl.len == ARM_BREAKPOINT_LEN_8)
+				alignment_mask = 0x7;
+			else
+				alignment_mask = 0x3;
+		} else {
+			alignment_mask = 0x7;
+		}
+
+		/* Check if the watchpoint value matches. */
+		val = read_wb_reg(AARCH64_DBG_REG_WVR, i);
+		if (val != (addr & ~alignment_mask))
+			goto unlock;
+
+		/* Possible match, check the byte address select to confirm. */
+		ctrl_reg = read_wb_reg(AARCH64_DBG_REG_WCR, i);
+		decode_ctrl_reg(ctrl_reg, &ctrl);
+		if (!((1 << (addr & alignment_mask)) & ctrl.len))
+			goto unlock;
+
+		/*
+		 * Check that the access type matches.
+		 * 0 => load, otherwise => store
+		 */
+		access = (esr & AARCH64_ESR_ACCESS_MASK) ? HW_BREAKPOINT_W :
+			 HW_BREAKPOINT_R;
+		if (!(access & hw_breakpoint_type(wp)))
+			goto unlock;
+
+		info->trigger = addr;
+		perf_bp_event(wp, regs);
+
+		/* Do we need to handle the stepping? */
+		if (!wp->overflow_handler)
+			step = 1;
+
+unlock:
+		rcu_read_unlock();
+	}
+
+	if (!step)
+		return 0;
+
+	/*
+	 * We always disable EL0 watchpoints because the kernel can
+	 * cause these to fire via an unprivileged access.
+	 */
+	toggle_bp_registers(AARCH64_DBG_REG_WCR, DBG_ACTIVE_EL0, 0);
+
+	if (user_mode(regs)) {
+		debug_info->wps_disabled = 1;
+
+		/* If we're already stepping a breakpoint, just return. */
+		if (debug_info->bps_disabled)
+			return 0;
+
+		if (test_thread_flag(TIF_SINGLESTEP))
+			debug_info->suspended_step = 1;
+		else
+			user_enable_single_step(current);
+	} else {
+		toggle_bp_registers(AARCH64_DBG_REG_WCR, DBG_ACTIVE_EL1, 0);
+		kernel_step = &__get_cpu_var(stepping_kernel_bp);
+
+		if (*kernel_step != ARM_KERNEL_STEP_NONE)
+			return 0;
+
+		if (kernel_active_single_step()) {
+			*kernel_step = ARM_KERNEL_STEP_SUSPEND;
+		} else {
+			*kernel_step = ARM_KERNEL_STEP_ACTIVE;
+			kernel_enable_single_step(regs);
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Handle single-step exception.
+ */
+int reinstall_suspended_bps(struct pt_regs *regs)
+{
+	struct debug_info *debug_info = &current->thread.debug;
+	int handled_exception = 0, *kernel_step;
+
+	kernel_step = &__get_cpu_var(stepping_kernel_bp);
+
+	/*
+	 * Called from single-step exception handler.
+	 * Return 0 if execution can resume, 1 if a SIGTRAP should be
+	 * reported.
+	 */
+	if (user_mode(regs)) {
+		if (debug_info->bps_disabled) {
+			debug_info->bps_disabled = 0;
+			toggle_bp_registers(AARCH64_DBG_REG_BCR, DBG_ACTIVE_EL0, 1);
+			handled_exception = 1;
+		}
+
+		if (debug_info->wps_disabled) {
+			debug_info->wps_disabled = 0;
+			toggle_bp_registers(AARCH64_DBG_REG_WCR, DBG_ACTIVE_EL0, 1);
+			handled_exception = 1;
+		}
+
+		if (handled_exception) {
+			if (debug_info->suspended_step) {
+				debug_info->suspended_step = 0;
+				/* Allow exception handling to fall-through. */
+				handled_exception = 0;
+			} else {
+				user_disable_single_step(current);
+			}
+		}
+	} else if (*kernel_step != ARM_KERNEL_STEP_NONE) {
+		toggle_bp_registers(AARCH64_DBG_REG_BCR, DBG_ACTIVE_EL1, 1);
+		toggle_bp_registers(AARCH64_DBG_REG_WCR, DBG_ACTIVE_EL1, 1);
+
+		if (!debug_info->wps_disabled)
+			toggle_bp_registers(AARCH64_DBG_REG_WCR, DBG_ACTIVE_EL0, 1);
+
+		if (*kernel_step != ARM_KERNEL_STEP_SUSPEND) {
+			kernel_disable_single_step();
+			handled_exception = 1;
+		} else {
+			handled_exception = 0;
+		}
+
+		*kernel_step = ARM_KERNEL_STEP_NONE;
+	}
+
+	return !handled_exception;
+}
+
+/*
+ * Context-switcher for restoring suspended breakpoints.
+ */
+void hw_breakpoint_thread_switch(struct task_struct *next)
+{
+	/*
+	 *           current        next
+	 * disabled: 0              0     => The usual case, NOTIFY_DONE
+	 *           0              1     => Disable the registers
+	 *           1              0     => Enable the registers
+	 *           1              1     => NOTIFY_DONE. per-task bps will
+	 *                                   get taken care of by perf.
+	 */
+
+	struct debug_info *current_debug_info, *next_debug_info;
+
+	current_debug_info = &current->thread.debug;
+	next_debug_info = &next->thread.debug;
+
+	/* Update breakpoints. */
+	if (current_debug_info->bps_disabled != next_debug_info->bps_disabled)
+		toggle_bp_registers(AARCH64_DBG_REG_BCR,
+				    DBG_ACTIVE_EL0,
+				    !next_debug_info->bps_disabled);
+
+	/* Update watchpoints. */
+	if (current_debug_info->wps_disabled != next_debug_info->wps_disabled)
+		toggle_bp_registers(AARCH64_DBG_REG_WCR,
+				    DBG_ACTIVE_EL0,
+				    !next_debug_info->wps_disabled);
+}
+
+/*
+ * CPU initialisation.
+ */
+static void reset_ctrl_regs(void *unused)
+{
+	int i;
+
+	for (i = 0; i < core_num_brps; ++i) {
+		write_wb_reg(AARCH64_DBG_REG_BCR, i, 0UL);
+		write_wb_reg(AARCH64_DBG_REG_BVR, i, 0UL);
+	}
+
+	for (i = 0; i < core_num_wrps; ++i) {
+		write_wb_reg(AARCH64_DBG_REG_WCR, i, 0UL);
+		write_wb_reg(AARCH64_DBG_REG_WVR, i, 0UL);
+	}
+}
+
+static int __cpuinit hw_breakpoint_reset_notify(struct notifier_block *self,
+						unsigned long action,
+						void *hcpu)
+{
+	int cpu = (long)hcpu;
+	if (action == CPU_ONLINE)
+		smp_call_function_single(cpu, reset_ctrl_regs, NULL, 1);
+	return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata hw_breakpoint_reset_nb = {
+	.notifier_call = hw_breakpoint_reset_notify,
+};
+
+/*
+ * One-time initialisation.
+ */
+static int __init arch_hw_breakpoint_init(void)
+{
+	core_num_brps = get_num_brps();
+	core_num_wrps = get_num_wrps();
+
+	pr_info("found %d breakpoint and %d watchpoint registers.\n",
+		core_num_brps, core_num_wrps);
+
+	/*
+	 * Reset the breakpoint resources. We assume that a halting
+	 * debugger will leave the world in a nice state for us.
+	 */
+	smp_call_function(reset_ctrl_regs, NULL, 1);
+	reset_ctrl_regs(NULL);
+
+	/* Register debug fault handlers. */
+	hook_debug_fault_code(DBG_ESR_EVT_HWBP, breakpoint_handler, SIGTRAP,
+			      TRAP_HWBKPT, "hw-breakpoint handler");
+	hook_debug_fault_code(DBG_ESR_EVT_HWWP, watchpoint_handler, SIGTRAP,
+			      TRAP_HWBKPT, "hw-watchpoint handler");
+
+	/* Register hotplug notifier. */
+	register_cpu_notifier(&hw_breakpoint_reset_nb);
+
+	return 0;
+}
+arch_initcall(arch_hw_breakpoint_init);
+
+void hw_breakpoint_pmu_read(struct perf_event *bp)
+{
+}
+
+/*
+ * Dummy function to register with die_notifier.
+ */
+int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
+				    unsigned long val, void *data)
+{
+	return NOTIFY_DONE;
+}