/*
 * 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.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 (is_default_overflow_handler(bp))
                        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 (is_default_overflow_handler(wp))
                        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;
}