/*
 * arch/sh/kernel/hw_breakpoint.c
 *
 * Unified kernel/user-space hardware breakpoint facility for the on-chip UBC.
 *
 * Copyright (C) 2009 - 2010  Paul Mundt
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 */
#include <linux/init.h>
#include <linux/perf_event.h>
#include <linux/sched/signal.h>
#include <linux/hw_breakpoint.h>
#include <linux/percpu.h>
#include <linux/kallsyms.h>
#include <linux/notifier.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/io.h>
#include <linux/clk.h>
#include <asm/hw_breakpoint.h>
#include <asm/mmu_context.h>
#include <asm/ptrace.h>
#include <asm/traps.h>

/*
 * 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]);

/*
 * A dummy placeholder for early accesses until the CPUs get a chance to
 * register their UBCs later in the boot process.
 */
static struct sh_ubc ubc_dummy = { .num_events = 0 };

static struct sh_ubc *sh_ubc __read_mostly = &ubc_dummy;

/*
 * Install a perf counter breakpoint.
 *
 * We seek a free UBC channel and use it for this breakpoint.
 *
 * 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);
        int i;

        for (i = 0; i < sh_ubc->num_events; i++) {
                struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);

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

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

        clk_enable(sh_ubc->clk);
        sh_ubc->enable(info, i);

        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);
        int i;

        for (i = 0; i < sh_ubc->num_events; i++) {
                struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);

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

        if (WARN_ONCE(i == sh_ubc->num_events, "Can't find any breakpoint slot"))
                return;

        sh_ubc->disable(info, i);
        clk_disable(sh_ubc->clk);
}

static int get_hbp_len(u16 hbp_len)
{
        unsigned int len_in_bytes = 0;

        switch (hbp_len) {
        case SH_BREAKPOINT_LEN_1:
                len_in_bytes = 1;
                break;
        case SH_BREAKPOINT_LEN_2:
                len_in_bytes = 2;
                break;
        case SH_BREAKPOINT_LEN_4:
                len_in_bytes = 4;
                break;
        case SH_BREAKPOINT_LEN_8:
                len_in_bytes = 8;
                break;
        }
        return len_in_bytes;
}

/*
 * Check for virtual address in kernel space.
 */
int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw)
{
        unsigned int len;
        unsigned long va;

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

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

int arch_bp_generic_fields(int sh_len, int sh_type,
                           int *gen_len, int *gen_type)
{
        /* Len */
        switch (sh_len) {
        case SH_BREAKPOINT_LEN_1:
                *gen_len = HW_BREAKPOINT_LEN_1;
                break;
        case SH_BREAKPOINT_LEN_2:
                *gen_len = HW_BREAKPOINT_LEN_2;
                break;
        case SH_BREAKPOINT_LEN_4:
                *gen_len = HW_BREAKPOINT_LEN_4;
                break;
        case SH_BREAKPOINT_LEN_8:
                *gen_len = HW_BREAKPOINT_LEN_8;
                break;
        default:
                return -EINVAL;
        }

        /* Type */
        switch (sh_type) {
        case SH_BREAKPOINT_READ:
                *gen_type = HW_BREAKPOINT_R;
        case SH_BREAKPOINT_WRITE:
                *gen_type = HW_BREAKPOINT_W;
                break;
        case SH_BREAKPOINT_RW:
                *gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
                break;
        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;

        /* Len */
        switch (bp->attr.bp_len) {
        case HW_BREAKPOINT_LEN_1:
                info->len = SH_BREAKPOINT_LEN_1;
                break;
        case HW_BREAKPOINT_LEN_2:
                info->len = SH_BREAKPOINT_LEN_2;
                break;
        case HW_BREAKPOINT_LEN_4:
                info->len = SH_BREAKPOINT_LEN_4;
                break;
        case HW_BREAKPOINT_LEN_8:
                info->len = SH_BREAKPOINT_LEN_8;
                break;
        default:
                return -EINVAL;
        }

        /* Type */
        switch (bp->attr.bp_type) {
        case HW_BREAKPOINT_R:
                info->type = SH_BREAKPOINT_READ;
                break;
        case HW_BREAKPOINT_W:
                info->type = SH_BREAKPOINT_WRITE;
                break;
        case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
                info->type = SH_BREAKPOINT_RW;
                break;
        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 SH_BREAKPOINT_LEN_1:
                align = 0;
                break;
        case SH_BREAKPOINT_LEN_2:
                align = 1;
                break;
        case SH_BREAKPOINT_LEN_4:
                align = 3;
                break;
        case SH_BREAKPOINT_LEN_8:
                align = 7;
                break;
        default:
                return ret;
        }

        /*
         * For kernel-addresses, either the address or symbol name can be
         * specified.
         */
        if (info->name)
                info->address = (unsigned long)kallsyms_lookup_name(info->name);

        /*
         * 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;
}

/*
 * 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 < sh_ubc->num_events; i++) {
                unregister_hw_breakpoint(t->ptrace_bps[i]);
                t->ptrace_bps[i] = NULL;
        }
}

static int __kprobes hw_breakpoint_handler(struct die_args *args)
{
        int cpu, i, rc = NOTIFY_STOP;
        struct perf_event *bp;
        unsigned int cmf, resume_mask;

        /*
         * Do an early return if none of the channels triggered.
         */
        cmf = sh_ubc->triggered_mask();
        if (unlikely(!cmf))
                return NOTIFY_DONE;

        /*
         * By default, resume all of the active channels.
         */
        resume_mask = sh_ubc->active_mask();

        /*
         * Disable breakpoints during exception handling.
         */
        sh_ubc->disable_all();

        cpu = get_cpu();
        for (i = 0; i < sh_ubc->num_events; i++) {
                unsigned long event_mask = (1 << i);

                if (likely(!(cmf & event_mask)))
                        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);
                if (bp)
                        rc = NOTIFY_DONE;

                /*
                 * Reset the condition match flag to denote completion of
                 * exception handling.
                 */
                sh_ubc->clear_triggered_mask(event_mask);

                /*
                 * bp can be NULL due to concurrent perf counter
                 * removing.
                 */
                if (!bp) {
                        rcu_read_unlock();
                        break;
                }

                /*
                 * Don't restore the channel if the breakpoint is from
                 * ptrace, as it always operates in one-shot mode.
                 */
                if (bp->overflow_handler == ptrace_triggered)
                        resume_mask &= ~(1 << i);

                perf_bp_event(bp, args->regs);

                /* Deliver the signal to userspace */
                if (!arch_check_bp_in_kernelspace(&bp->hw.info)) {
                        force_sig_fault(SIGTRAP, TRAP_HWBKPT,
                                        (void __user *)NULL, current);
                }

                rcu_read_unlock();
        }

        if (cmf == 0)
                rc = NOTIFY_DONE;

        sh_ubc->enable_all(resume_mask);

        put_cpu();

        return rc;
}

BUILD_TRAP_HANDLER(breakpoint)
{
        unsigned long ex = lookup_exception_vector();
        TRAP_HANDLER_DECL;

        notify_die(DIE_BREAKPOINT, "breakpoint", regs, 0, ex, SIGTRAP);
}

/*
 * Handle debug exception notifications.
 */
int __kprobes hw_breakpoint_exceptions_notify(struct notifier_block *unused,
                                    unsigned long val, void *data)
{
        struct die_args *args = data;

        if (val != DIE_BREAKPOINT)
                return NOTIFY_DONE;

        /*
         * If the breakpoint hasn't been triggered by the UBC, it's
         * probably from a debugger, so don't do anything more here.
         *
         * This also permits the UBC interface clock to remain off for
         * non-UBC breakpoints, as we don't need to check the triggered
         * or active channel masks.
         */
        if (args->trapnr != sh_ubc->trap_nr)
                return NOTIFY_DONE;

        return hw_breakpoint_handler(data);
}

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

int register_sh_ubc(struct sh_ubc *ubc)
{
        /* Bail if it's already assigned */
        if (sh_ubc != &ubc_dummy)
                return -EBUSY;
        sh_ubc = ubc;

        pr_info("HW Breakpoints: %s UBC support registered\n", ubc->name);

        WARN_ON(ubc->num_events > HBP_NUM);

        return 0;
}