mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race

[linux/fpc-iii.git] / arch / arm / kernel / hw_breakpoint.c

/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (C) 2009, 2010 ARM Limited
 *
 * Author: Will Deacon <will.deacon@arm.com>
 */

/*
 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
 * using the CPU's debug registers.
 */
#define pr_fmt(fmt) "hw-breakpoint: " fmt

#include <linux/errno.h>
#include <linux/hardirq.h>
#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
#include <linux/smp.h>
#include <linux/cpu_pm.h>
#include <linux/coresight.h>

#include <asm/cacheflush.h>
#include <asm/cputype.h>
#include <asm/current.h>
#include <asm/hw_breakpoint.h>
#include <asm/traps.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]);

/* Number of BRP/WRP registers on this CPU. */
static int core_num_brps;
static int core_num_wrps;

/* Debug architecture version. */
static u8 debug_arch;

/* Does debug architecture support OS Save and Restore? */
static bool has_ossr;

/* Maximum supported watchpoint length. */
static u8 max_watchpoint_len;

#define READ_WB_REG_CASE(OP2, M, VAL)                   \
        case ((OP2 << 4) + M):                          \
                ARM_DBG_READ(c0, c ## M, OP2, VAL);     \
                break

#define WRITE_WB_REG_CASE(OP2, M, VAL)                  \
        case ((OP2 << 4) + M):                          \
                ARM_DBG_WRITE(c0, c ## M, OP2, VAL);    \
                break

#define GEN_READ_WB_REG_CASES(OP2, VAL)         \
        READ_WB_REG_CASE(OP2, 0, VAL);          \
        READ_WB_REG_CASE(OP2, 1, VAL);          \
        READ_WB_REG_CASE(OP2, 2, VAL);          \
        READ_WB_REG_CASE(OP2, 3, VAL);          \
        READ_WB_REG_CASE(OP2, 4, VAL);          \
        READ_WB_REG_CASE(OP2, 5, VAL);          \
        READ_WB_REG_CASE(OP2, 6, VAL);          \
        READ_WB_REG_CASE(OP2, 7, VAL);          \
        READ_WB_REG_CASE(OP2, 8, VAL);          \
        READ_WB_REG_CASE(OP2, 9, VAL);          \
        READ_WB_REG_CASE(OP2, 10, VAL);         \
        READ_WB_REG_CASE(OP2, 11, VAL);         \
        READ_WB_REG_CASE(OP2, 12, VAL);         \
        READ_WB_REG_CASE(OP2, 13, VAL);         \
        READ_WB_REG_CASE(OP2, 14, VAL);         \
        READ_WB_REG_CASE(OP2, 15, VAL)

#define GEN_WRITE_WB_REG_CASES(OP2, VAL)        \
        WRITE_WB_REG_CASE(OP2, 0, VAL);         \
        WRITE_WB_REG_CASE(OP2, 1, VAL);         \
        WRITE_WB_REG_CASE(OP2, 2, VAL);         \
        WRITE_WB_REG_CASE(OP2, 3, VAL);         \
        WRITE_WB_REG_CASE(OP2, 4, VAL);         \
        WRITE_WB_REG_CASE(OP2, 5, VAL);         \
        WRITE_WB_REG_CASE(OP2, 6, VAL);         \
        WRITE_WB_REG_CASE(OP2, 7, VAL);         \
        WRITE_WB_REG_CASE(OP2, 8, VAL);         \
        WRITE_WB_REG_CASE(OP2, 9, VAL);         \
        WRITE_WB_REG_CASE(OP2, 10, VAL);        \
        WRITE_WB_REG_CASE(OP2, 11, VAL);        \
        WRITE_WB_REG_CASE(OP2, 12, VAL);        \
        WRITE_WB_REG_CASE(OP2, 13, VAL);        \
        WRITE_WB_REG_CASE(OP2, 14, VAL);        \
        WRITE_WB_REG_CASE(OP2, 15, VAL)

static u32 read_wb_reg(int n)
{
        u32 val = 0;

        switch (n) {
        GEN_READ_WB_REG_CASES(ARM_OP2_BVR, val);
        GEN_READ_WB_REG_CASES(ARM_OP2_BCR, val);
        GEN_READ_WB_REG_CASES(ARM_OP2_WVR, val);
        GEN_READ_WB_REG_CASES(ARM_OP2_WCR, val);
        default:
                pr_warn("attempt to read from unknown breakpoint register %d\n",
                        n);
        }

        return val;
}

static void write_wb_reg(int n, u32 val)
{
        switch (n) {
        GEN_WRITE_WB_REG_CASES(ARM_OP2_BVR, val);
        GEN_WRITE_WB_REG_CASES(ARM_OP2_BCR, val);
        GEN_WRITE_WB_REG_CASES(ARM_OP2_WVR, val);
        GEN_WRITE_WB_REG_CASES(ARM_OP2_WCR, val);
        default:
                pr_warn("attempt to write to unknown breakpoint register %d\n",
                        n);
        }
        isb();
}

/* Determine debug architecture. */
static u8 get_debug_arch(void)
{
        u32 didr;

        /* Do we implement the extended CPUID interface? */
        if (((read_cpuid_id() >> 16) & 0xf) != 0xf) {
                pr_warn_once("CPUID feature registers not supported. "
                             "Assuming v6 debug is present.\n");
                return ARM_DEBUG_ARCH_V6;
        }

        ARM_DBG_READ(c0, c0, 0, didr);
        return (didr >> 16) & 0xf;
}

u8 arch_get_debug_arch(void)
{
        return debug_arch;
}

static int debug_arch_supported(void)
{
        u8 arch = get_debug_arch();

        /* We don't support the memory-mapped interface. */
        return (arch >= ARM_DEBUG_ARCH_V6 && arch <= ARM_DEBUG_ARCH_V7_ECP14) ||
                arch >= ARM_DEBUG_ARCH_V7_1;
}

/* Can we determine the watchpoint access type from the fsr? */
static int debug_exception_updates_fsr(void)
{
        return get_debug_arch() >= ARM_DEBUG_ARCH_V8;
}

/* Determine number of WRP registers available. */
static int get_num_wrp_resources(void)
{
        u32 didr;
        ARM_DBG_READ(c0, c0, 0, didr);
        return ((didr >> 28) & 0xf) + 1;
}

/* Determine number of BRP registers available. */
static int get_num_brp_resources(void)
{
        u32 didr;
        ARM_DBG_READ(c0, c0, 0, didr);
        return ((didr >> 24) & 0xf) + 1;
}

/* Does this core support mismatch breakpoints? */
static int core_has_mismatch_brps(void)
{
        return (get_debug_arch() >= ARM_DEBUG_ARCH_V7_ECP14 &&
                get_num_brp_resources() > 1);
}

/* Determine number of usable WRPs available. */
static int get_num_wrps(void)
{
        /*
         * On debug architectures prior to 7.1, when a watchpoint fires, the
         * only way to work out which watchpoint it was is by disassembling
         * the faulting instruction and working out the address of the memory
         * access.
         *
         * Furthermore, we can only do this if the watchpoint was precise
         * since imprecise watchpoints prevent us from calculating register
         * based addresses.
         *
         * Providing we have more than 1 breakpoint register, we only report
         * a single watchpoint register for the time being. This way, we always
         * know which watchpoint fired. In the future we can either add a
         * disassembler and address generation emulator, or we can insert a
         * check to see if the DFAR is set on watchpoint exception entry
         * [the ARM ARM states that the DFAR is UNKNOWN, but experience shows
         * that it is set on some implementations].
         */
        if (get_debug_arch() < ARM_DEBUG_ARCH_V7_1)
                return 1;

        return get_num_wrp_resources();
}

/* Determine number of usable BRPs available. */
static int get_num_brps(void)
{
        int brps = get_num_brp_resources();
        return core_has_mismatch_brps() ? brps - 1 : brps;
}

/*
 * In order to access the breakpoint/watchpoint control registers,
 * we must be running in debug monitor mode. Unfortunately, we can
 * be put into halting debug mode at any time by an external debugger
 * but there is nothing we can do to prevent that.
 */
static int monitor_mode_enabled(void)
{
        u32 dscr;
        ARM_DBG_READ(c0, c1, 0, dscr);
        return !!(dscr & ARM_DSCR_MDBGEN);
}

static int enable_monitor_mode(void)
{
        u32 dscr;
        ARM_DBG_READ(c0, c1, 0, dscr);

        /* If monitor mode is already enabled, just return. */
        if (dscr & ARM_DSCR_MDBGEN)
                goto out;

        /* Write to the corresponding DSCR. */
        switch (get_debug_arch()) {
        case ARM_DEBUG_ARCH_V6:
        case ARM_DEBUG_ARCH_V6_1:
                ARM_DBG_WRITE(c0, c1, 0, (dscr | ARM_DSCR_MDBGEN));
                break;
        case ARM_DEBUG_ARCH_V7_ECP14:
        case ARM_DEBUG_ARCH_V7_1:
        case ARM_DEBUG_ARCH_V8:
                ARM_DBG_WRITE(c0, c2, 2, (dscr | ARM_DSCR_MDBGEN));
                isb();
                break;
        default:
                return -ENODEV;
        }

        /* Check that the write made it through. */
        ARM_DBG_READ(c0, c1, 0, dscr);
        if (!(dscr & ARM_DSCR_MDBGEN)) {
                pr_warn_once("Failed to enable monitor mode on CPU %d.\n",
                                smp_processor_id());
                return -EPERM;
        }

out:
        return 0;
}

int hw_breakpoint_slots(int type)
{
        if (!debug_arch_supported())
                return 0;

        /*
         * 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_warn("unknown slot type: %d\n", type);
                return 0;
        }
}

/*
 * Check if 8-bit byte-address select is available.
 * This clobbers WRP 0.
 */
static u8 get_max_wp_len(void)
{
        u32 ctrl_reg;
        struct arch_hw_breakpoint_ctrl ctrl;
        u8 size = 4;

        if (debug_arch < ARM_DEBUG_ARCH_V7_ECP14)
                goto out;

        memset(&ctrl, 0, sizeof(ctrl));
        ctrl.len = ARM_BREAKPOINT_LEN_8;
        ctrl_reg = encode_ctrl_reg(ctrl);

        write_wb_reg(ARM_BASE_WVR, 0);
        write_wb_reg(ARM_BASE_WCR, ctrl_reg);
        if ((read_wb_reg(ARM_BASE_WCR) & ctrl_reg) == ctrl_reg)
                size = 8;

out:
        return size;
}

u8 arch_get_max_wp_len(void)
{
        return max_watchpoint_len;
}

/*
 * 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;
        int i, max_slots, ctrl_base, val_base;
        u32 addr, ctrl;

        addr = info->address;
        ctrl = encode_ctrl_reg(info->ctrl) | 0x1;

        if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE) {
                /* Breakpoint */
                ctrl_base = ARM_BASE_BCR;
                val_base = ARM_BASE_BVR;
                slots = this_cpu_ptr(bp_on_reg);
                max_slots = core_num_brps;
        } else {
                /* Watchpoint */
                ctrl_base = ARM_BASE_WCR;
                val_base = ARM_BASE_WVR;
                slots = this_cpu_ptr(wp_on_reg);
                max_slots = core_num_wrps;
        }

        for (i = 0; i < max_slots; ++i) {
                slot = &slots[i];

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

        if (i == max_slots) {
                pr_warn("Can't find any breakpoint slot\n");
                return -EBUSY;
        }

        /* Override the breakpoint data with the step data. */
        if (info->step_ctrl.enabled) {
                addr = info->trigger & ~0x3;
                ctrl = encode_ctrl_reg(info->step_ctrl);
                if (info->ctrl.type != ARM_BREAKPOINT_EXECUTE) {
                        i = 0;
                        ctrl_base = ARM_BASE_BCR + core_num_brps;
                        val_base = ARM_BASE_BVR + core_num_brps;
                }
        }

        /* Setup the address register. */
        write_wb_reg(val_base + i, addr);

        /* Setup the control register. */
        write_wb_reg(ctrl_base + i, ctrl);
        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 = ARM_BASE_BCR;
                slots = this_cpu_ptr(bp_on_reg);
                max_slots = core_num_brps;
        } else {
                /* Watchpoint */
                base = ARM_BASE_WCR;
                slots = this_cpu_ptr(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 (i == max_slots) {
                pr_warn("Can't find any breakpoint slot\n");
                return;
        }

        /* Ensure that we disable the mismatch breakpoint. */
        if (info->ctrl.type != ARM_BREAKPOINT_EXECUTE &&
            info->step_ctrl.enabled) {
                i = 0;
                base = ARM_BASE_BCR + core_num_brps;
        }

        /* Reset the control register. */
        write_wb_reg(base + i, 0);
}

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;
                if ((info->ctrl.type != ARM_BREAKPOINT_EXECUTE)
                        && max_watchpoint_len >= 8)
                        break;
        default:
                return -EINVAL;
        }

        /*
         * Breakpoints must be of length 2 (thumb) or 4 (ARM) bytes.
         * Watchpoints can be of length 1, 2, 4 or 8 bytes if supported
         * by the hardware and must be aligned to the appropriate number of
         * bytes.
         */
        if (info->ctrl.type == ARM_BREAKPOINT_EXECUTE &&
            info->ctrl.len != ARM_BREAKPOINT_LEN_2 &&
            info->ctrl.len != ARM_BREAKPOINT_LEN_4)
                return -EINVAL;

        /* Address */
        info->address = bp->attr.bp_addr;

        /* Privilege */
        info->ctrl.privilege = ARM_BREAKPOINT_USER;
        if (arch_check_bp_in_kernelspace(bp))
                info->ctrl.privilege |= ARM_BREAKPOINT_PRIV;

        /* Enabled? */
        info->ctrl.enabled = !bp->attr.disabled;

        /* Mismatch */
        info->ctrl.mismatch = 0;

        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 = 0;
        u32 offset, alignment_mask = 0x3;

        /* Ensure that we are in monitor debug mode. */
        if (!monitor_mode_enabled())
                return -ENODEV;

        /* Build the arch_hw_breakpoint. */
        ret = arch_build_bp_info(bp);
        if (ret)
                goto out;

        /* Check address alignment. */
        if (info->ctrl.len == ARM_BREAKPOINT_LEN_8)
                alignment_mask = 0x7;
        offset = info->address & alignment_mask;
        switch (offset) {
        case 0:
                /* Aligned */
                break;
        case 1:
        case 2:
                /* Allow halfword watchpoints and breakpoints. */
                if (info->ctrl.len == ARM_BREAKPOINT_LEN_2)
                        break;
        case 3:
                /* Allow single byte watchpoint. */
                if (info->ctrl.len == ARM_BREAKPOINT_LEN_1)
                        break;
        default:
                ret = -EINVAL;
                goto out;
        }

        info->address &= ~alignment_mask;
        info->ctrl.len <<= offset;

        if (is_default_overflow_handler(bp)) {
                /*
                 * Mismatch breakpoints are required for single-stepping
                 * breakpoints.
                 */
                if (!core_has_mismatch_brps())
                        return -EINVAL;

                /* We don't allow mismatch breakpoints in kernel space. */
                if (arch_check_bp_in_kernelspace(bp))
                        return -EPERM;

                /*
                 * Per-cpu breakpoints are not supported by our stepping
                 * mechanism.
                 */
                if (!bp->hw.target)
                        return -EINVAL;

                /*
                 * We only support specific access types if the fsr
                 * reports them.
                 */
                if (!debug_exception_updates_fsr() &&
                    (info->ctrl.type == ARM_BREAKPOINT_LOAD ||
                     info->ctrl.type == ARM_BREAKPOINT_STORE))
                        return -EINVAL;
        }

out:
        return ret;
}

/*
 * Enable/disable single-stepping over the breakpoint bp at address addr.
 */
static void enable_single_step(struct perf_event *bp, u32 addr)
{
        struct arch_hw_breakpoint *info = counter_arch_bp(bp);

        arch_uninstall_hw_breakpoint(bp);
        info->step_ctrl.mismatch  = 1;
        info->step_ctrl.len       = ARM_BREAKPOINT_LEN_4;
        info->step_ctrl.type      = ARM_BREAKPOINT_EXECUTE;
        info->step_ctrl.privilege = info->ctrl.privilege;
        info->step_ctrl.enabled   = 1;
        info->trigger             = addr;
        arch_install_hw_breakpoint(bp);
}

static void disable_single_step(struct perf_event *bp)
{
        arch_uninstall_hw_breakpoint(bp);
        counter_arch_bp(bp)->step_ctrl.enabled = 0;
        arch_install_hw_breakpoint(bp);
}

/*
 * Arm32 hardware does not always report a watchpoint hit address that matches
 * one of the watchpoints set. It can also report an address "near" the
 * watchpoint if a single instruction access both watched and unwatched
 * addresses. There is no straight-forward way, short of disassembling the
 * offending instruction, to map that address back to the watchpoint. This
 * function computes the distance of the memory access from the watchpoint as a
 * heuristic for the likelyhood that a given access triggered the watchpoint.
 *
 * See this same function in the arm64 platform code, which has the same
 * problem.
 *
 * The function returns the distance of the address from the bytes watched by
 * the watchpoint. In case of an exact match, it returns 0.
 */
static u32 get_distance_from_watchpoint(unsigned long addr, u32 val,
                                        struct arch_hw_breakpoint_ctrl *ctrl)
{
        u32 wp_low, wp_high;
        u32 lens, lene;

        lens = __ffs(ctrl->len);
        lene = __fls(ctrl->len);

        wp_low = val + lens;
        wp_high = val + lene;
        if (addr < wp_low)
                return wp_low - addr;
        else if (addr > wp_high)
                return addr - wp_high;
        else
                return 0;
}

static int watchpoint_fault_on_uaccess(struct pt_regs *regs,
                                       struct arch_hw_breakpoint *info)
{
        return !user_mode(regs) && info->ctrl.privilege == ARM_BREAKPOINT_USER;
}

static void watchpoint_handler(unsigned long addr, unsigned int fsr,
                               struct pt_regs *regs)
{
        int i, access, closest_match = 0;
        u32 min_dist = -1, dist;
        u32 val, ctrl_reg;
        struct perf_event *wp, **slots;
        struct arch_hw_breakpoint *info;
        struct arch_hw_breakpoint_ctrl ctrl;

        slots = this_cpu_ptr(wp_on_reg);

        /*
         * Find all watchpoints that match the reported address. If no exact
         * match is found. Attribute the hit to the closest watchpoint.
         */
        rcu_read_lock();
        for (i = 0; i < core_num_wrps; ++i) {
                wp = slots[i];
                if (wp == NULL)
                        continue;

                /*
                 * The DFAR is an unknown value on debug architectures prior
                 * to 7.1. Since we only allow a single watchpoint on these
                 * older CPUs, we can set the trigger to the lowest possible
                 * faulting address.
                 */
                if (debug_arch < ARM_DEBUG_ARCH_V7_1) {
                        BUG_ON(i > 0);
                        info = counter_arch_bp(wp);
                        info->trigger = wp->attr.bp_addr;
                } else {
                        /* Check that the access type matches. */
                        if (debug_exception_updates_fsr()) {
                                access = (fsr & ARM_FSR_ACCESS_MASK) ?
                                          HW_BREAKPOINT_W : HW_BREAKPOINT_R;
                                if (!(access & hw_breakpoint_type(wp)))
                                        continue;
                        }

                        val = read_wb_reg(ARM_BASE_WVR + i);
                        ctrl_reg = read_wb_reg(ARM_BASE_WCR + i);
                        decode_ctrl_reg(ctrl_reg, &ctrl);
                        dist = get_distance_from_watchpoint(addr, val, &ctrl);
                        if (dist < min_dist) {
                                min_dist = dist;
                                closest_match = i;
                        }
                        /* Is this an exact match? */
                        if (dist != 0)
                                continue;

                        /* We have a winner. */
                        info = counter_arch_bp(wp);
                        info->trigger = addr;
                }

                pr_debug("watchpoint fired: address = 0x%x\n", info->trigger);

                /*
                 * If we triggered a user watchpoint from a uaccess routine,
                 * then handle the stepping ourselves since userspace really
                 * can't help us with this.
                 */
                if (watchpoint_fault_on_uaccess(regs, info))
                        goto step;

                perf_bp_event(wp, regs);

                /*
                 * Defer stepping to the overflow handler if one is installed.
                 * Otherwise, insert a temporary mismatch breakpoint so that
                 * we can single-step over the watchpoint trigger.
                 */
                if (!is_default_overflow_handler(wp))
                        continue;
step:
                enable_single_step(wp, instruction_pointer(regs));
        }

        if (min_dist > 0 && min_dist != -1) {
                /* No exact match found. */
                wp = slots[closest_match];
                info = counter_arch_bp(wp);
                info->trigger = addr;
                pr_debug("watchpoint fired: address = 0x%x\n", info->trigger);
                perf_bp_event(wp, regs);
                if (is_default_overflow_handler(wp))
                        enable_single_step(wp, instruction_pointer(regs));
        }

        rcu_read_unlock();
}

static void watchpoint_single_step_handler(unsigned long pc)
{
        int i;
        struct perf_event *wp, **slots;
        struct arch_hw_breakpoint *info;

        slots = this_cpu_ptr(wp_on_reg);

        for (i = 0; i < core_num_wrps; ++i) {
                rcu_read_lock();

                wp = slots[i];

                if (wp == NULL)
                        goto unlock;

                info = counter_arch_bp(wp);
                if (!info->step_ctrl.enabled)
                        goto unlock;

                /*
                 * Restore the original watchpoint if we've completed the
                 * single-step.
                 */
                if (info->trigger != pc)
                        disable_single_step(wp);

unlock:
                rcu_read_unlock();
        }
}

static void breakpoint_handler(unsigned long unknown, struct pt_regs *regs)
{
        int i;
        u32 ctrl_reg, val, addr;
        struct perf_event *bp, **slots;
        struct arch_hw_breakpoint *info;
        struct arch_hw_breakpoint_ctrl ctrl;

        slots = this_cpu_ptr(bp_on_reg);

        /* The exception entry code places the amended lr in the PC. */
        addr = regs->ARM_pc;

        /* Check the currently installed breakpoints first. */
        for (i = 0; i < core_num_brps; ++i) {
                rcu_read_lock();

                bp = slots[i];

                if (bp == NULL)
                        goto unlock;

                info = counter_arch_bp(bp);

                /* Check if the breakpoint value matches. */
                val = read_wb_reg(ARM_BASE_BVR + i);
                if (val != (addr & ~0x3))
                        goto mismatch;

                /* Possible match, check the byte address select to confirm. */
                ctrl_reg = read_wb_reg(ARM_BASE_BCR + i);
                decode_ctrl_reg(ctrl_reg, &ctrl);
                if ((1 << (addr & 0x3)) & ctrl.len) {
                        info->trigger = addr;
                        pr_debug("breakpoint fired: address = 0x%x\n", addr);
                        perf_bp_event(bp, regs);
                        if (!bp->overflow_handler)
                                enable_single_step(bp, addr);
                        goto unlock;
                }

mismatch:
                /* If we're stepping a breakpoint, it can now be restored. */
                if (info->step_ctrl.enabled)
                        disable_single_step(bp);
unlock:
                rcu_read_unlock();
        }

        /* Handle any pending watchpoint single-step breakpoints. */
        watchpoint_single_step_handler(addr);
}

/*
 * Called from either the Data Abort Handler [watchpoint] or the
 * Prefetch Abort Handler [breakpoint] with interrupts disabled.
 */
static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr,
                                 struct pt_regs *regs)
{
        int ret = 0;
        u32 dscr;

        preempt_disable();

        if (interrupts_enabled(regs))
                local_irq_enable();

        /* We only handle watchpoints and hardware breakpoints. */
        ARM_DBG_READ(c0, c1, 0, dscr);

        /* Perform perf callbacks. */
        switch (ARM_DSCR_MOE(dscr)) {
        case ARM_ENTRY_BREAKPOINT:
                breakpoint_handler(addr, regs);
                break;
        case ARM_ENTRY_ASYNC_WATCHPOINT:
                WARN(1, "Asynchronous watchpoint exception taken. Debugging results may be unreliable\n");
        case ARM_ENTRY_SYNC_WATCHPOINT:
                watchpoint_handler(addr, fsr, regs);
                break;
        default:
                ret = 1; /* Unhandled fault. */
        }

        preempt_enable();

        return ret;
}

/*
 * One-time initialisation.
 */
static cpumask_t debug_err_mask;

static int debug_reg_trap(struct pt_regs *regs, unsigned int instr)
{
        int cpu = smp_processor_id();

        pr_warn("Debug register access (0x%x) caused undefined instruction on CPU %d\n",
                instr, cpu);

        /* Set the error flag for this CPU and skip the faulting instruction. */
        cpumask_set_cpu(cpu, &debug_err_mask);
        instruction_pointer(regs) += 4;
        return 0;
}

static struct undef_hook debug_reg_hook = {
        .instr_mask     = 0x0fe80f10,
        .instr_val      = 0x0e000e10,
        .fn             = debug_reg_trap,
};

/* Does this core support OS Save and Restore? */
static bool core_has_os_save_restore(void)
{
        u32 oslsr;

        switch (get_debug_arch()) {
        case ARM_DEBUG_ARCH_V7_1:
                return true;
        case ARM_DEBUG_ARCH_V7_ECP14:
                ARM_DBG_READ(c1, c1, 4, oslsr);
                if (oslsr & ARM_OSLSR_OSLM0)
                        return true;
        default:
                return false;
        }
}

static void reset_ctrl_regs(unsigned int cpu)
{
        int i, raw_num_brps, err = 0;
        u32 val;

        /*
         * v7 debug contains save and restore registers so that debug state
         * can be maintained across low-power modes without leaving the debug
         * logic powered up. It is IMPLEMENTATION DEFINED whether we can access
         * the debug registers out of reset, so we must unlock the OS Lock
         * Access Register to avoid taking undefined instruction exceptions
         * later on.
         */
        switch (debug_arch) {
        case ARM_DEBUG_ARCH_V6:
        case ARM_DEBUG_ARCH_V6_1:
                /* ARMv6 cores clear the registers out of reset. */
                goto out_mdbgen;
        case ARM_DEBUG_ARCH_V7_ECP14:
                /*
                 * Ensure sticky power-down is clear (i.e. debug logic is
                 * powered up).
                 */
                ARM_DBG_READ(c1, c5, 4, val);
                if ((val & 0x1) == 0)
                        err = -EPERM;

                if (!has_ossr)
                        goto clear_vcr;
                break;
        case ARM_DEBUG_ARCH_V7_1:
                /*
                 * Ensure the OS double lock is clear.
                 */
                ARM_DBG_READ(c1, c3, 4, val);
                if ((val & 0x1) == 1)
                        err = -EPERM;
                break;
        }

        if (err) {
                pr_warn_once("CPU %d debug is powered down!\n", cpu);
                cpumask_or(&debug_err_mask, &debug_err_mask, cpumask_of(cpu));
                return;
        }

        /*
         * Unconditionally clear the OS lock by writing a value
         * other than CS_LAR_KEY to the access register.
         */
        ARM_DBG_WRITE(c1, c0, 4, ~CORESIGHT_UNLOCK);
        isb();

        /*
         * Clear any configured vector-catch events before
         * enabling monitor mode.
         */
clear_vcr:
        ARM_DBG_WRITE(c0, c7, 0, 0);
        isb();

        if (cpumask_intersects(&debug_err_mask, cpumask_of(cpu))) {
                pr_warn_once("CPU %d failed to disable vector catch\n", cpu);
                return;
        }

        /*
         * The control/value register pairs are UNKNOWN out of reset so
         * clear them to avoid spurious debug events.
         */
        raw_num_brps = get_num_brp_resources();
        for (i = 0; i < raw_num_brps; ++i) {
                write_wb_reg(ARM_BASE_BCR + i, 0UL);
                write_wb_reg(ARM_BASE_BVR + i, 0UL);
        }

        for (i = 0; i < core_num_wrps; ++i) {
                write_wb_reg(ARM_BASE_WCR + i, 0UL);
                write_wb_reg(ARM_BASE_WVR + i, 0UL);
        }

        if (cpumask_intersects(&debug_err_mask, cpumask_of(cpu))) {
                pr_warn_once("CPU %d failed to clear debug register pairs\n", cpu);
                return;
        }

        /*
         * Have a crack at enabling monitor mode. We don't actually need
         * it yet, but reporting an error early is useful if it fails.
         */
out_mdbgen:
        if (enable_monitor_mode())
                cpumask_or(&debug_err_mask, &debug_err_mask, cpumask_of(cpu));
}

static int dbg_reset_online(unsigned int cpu)
{
        local_irq_disable();
        reset_ctrl_regs(cpu);
        local_irq_enable();
        return 0;
}

#ifdef CONFIG_CPU_PM
static int dbg_cpu_pm_notify(struct notifier_block *self, unsigned long action,
                             void *v)
{
        if (action == CPU_PM_EXIT)
                reset_ctrl_regs(smp_processor_id());

        return NOTIFY_OK;
}

static struct notifier_block dbg_cpu_pm_nb = {
        .notifier_call = dbg_cpu_pm_notify,
};

static void __init pm_init(void)
{
        cpu_pm_register_notifier(&dbg_cpu_pm_nb);
}
#else
static inline void pm_init(void)
{
}
#endif

static int __init arch_hw_breakpoint_init(void)
{
        int ret;

        debug_arch = get_debug_arch();

        if (!debug_arch_supported()) {
                pr_info("debug architecture 0x%x unsupported.\n", debug_arch);
                return 0;
        }

        /*
         * Scorpion CPUs (at least those in APQ8060) seem to set DBGPRSR.SPD
         * whenever a WFI is issued, even if the core is not powered down, in
         * violation of the architecture.  When DBGPRSR.SPD is set, accesses to
         * breakpoint and watchpoint registers are treated as undefined, so
         * this results in boot time and runtime failures when these are
         * accessed and we unexpectedly take a trap.
         *
         * It's not clear if/how this can be worked around, so we blacklist
         * Scorpion CPUs to avoid these issues.
        */
        if (read_cpuid_part() == ARM_CPU_PART_SCORPION) {
                pr_info("Scorpion CPU detected. Hardware breakpoints and watchpoints disabled\n");
                return 0;
        }

        has_ossr = core_has_os_save_restore();

        /* Determine how many BRPs/WRPs are available. */
        core_num_brps = get_num_brps();
        core_num_wrps = get_num_wrps();

        /*
         * We need to tread carefully here because DBGSWENABLE may be
         * driven low on this core and there isn't an architected way to
         * determine that.
         */
        cpus_read_lock();
        register_undef_hook(&debug_reg_hook);

        /*
         * Register CPU notifier which resets the breakpoint resources. We
         * assume that a halting debugger will leave the world in a nice state
         * for us.
         */
        ret = cpuhp_setup_state_cpuslocked(CPUHP_AP_ONLINE_DYN,
                                           "arm/hw_breakpoint:online",
                                           dbg_reset_online, NULL);
        unregister_undef_hook(&debug_reg_hook);
        if (WARN_ON(ret < 0) || !cpumask_empty(&debug_err_mask)) {
                core_num_brps = 0;
                core_num_wrps = 0;
                if (ret > 0)
                        cpuhp_remove_state_nocalls_cpuslocked(ret);
                cpus_read_unlock();
                return 0;
        }

        pr_info("found %d " "%s" "breakpoint and %d watchpoint registers.\n",
                core_num_brps, core_has_mismatch_brps() ? "(+1 reserved) " :
                "", core_num_wrps);

        /* Work out the maximum supported watchpoint length. */
        max_watchpoint_len = get_max_wp_len();
        pr_info("maximum watchpoint size is %u bytes.\n",
                        max_watchpoint_len);

        /* Register debug fault handler. */
        hook_fault_code(FAULT_CODE_DEBUG, hw_breakpoint_pending, SIGTRAP,
                        TRAP_HWBKPT, "watchpoint debug exception");
        hook_ifault_code(FAULT_CODE_DEBUG, hw_breakpoint_pending, SIGTRAP,
                        TRAP_HWBKPT, "breakpoint debug exception");
        cpus_read_unlock();

        /* Register PM notifiers. */
        pm_init();
        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;
}