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    Subject[PATCH v3 14/16] powerpc/watchpoint: Don't allow concurrent perf and ptrace events
    Date
    With Book3s DAWR, ptrace and perf watchpoints on powerpc behaves
    differently. Ptrace watchpoint works in one-shot mode and generates
    signal before executing instruction. It's ptrace user's job to
    single-step the instruction and re-enable the watchpoint. OTOH, in
    case of perf watchpoint, kernel emulates/single-steps the instruction
    and then generates event. If perf and ptrace creates two events with
    same or overlapping address ranges, it's ambiguous to decide who
    should single-step the instruction. Because of this issue, don't
    allow perf and ptrace watchpoint at the same time if their address
    range overlaps.

    Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
    ---
    arch/powerpc/include/asm/hw_breakpoint.h | 2 +
    arch/powerpc/kernel/hw_breakpoint.c | 222 +++++++++++++++++++++++
    kernel/events/hw_breakpoint.c | 16 ++
    3 files changed, 240 insertions(+)

    diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h
    index add5aa076919..f42a55eb77d2 100644
    --- a/arch/powerpc/include/asm/hw_breakpoint.h
    +++ b/arch/powerpc/include/asm/hw_breakpoint.h
    @@ -70,6 +70,8 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
    unsigned long val, void *data);
    int arch_install_hw_breakpoint(struct perf_event *bp);
    void arch_uninstall_hw_breakpoint(struct perf_event *bp);
    +int arch_reserve_bp_slot(struct perf_event *bp);
    +void arch_release_bp_slot(struct perf_event *bp);
    void arch_unregister_hw_breakpoint(struct perf_event *bp);
    void hw_breakpoint_pmu_read(struct perf_event *bp);
    extern void flush_ptrace_hw_breakpoint(struct task_struct *tsk);
    diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
    index 9b5812bca892..48c8b5edbc90 100644
    --- a/arch/powerpc/kernel/hw_breakpoint.c
    +++ b/arch/powerpc/kernel/hw_breakpoint.c
    @@ -123,6 +123,228 @@ static bool is_ptrace_bp(struct perf_event *bp)
    return bp->overflow_handler == ptrace_triggered;
    }

    +struct breakpoint {
    + struct list_head list;
    + struct perf_event *bp;
    + bool ptrace_bp;
    +};
    +
    +static DEFINE_PER_CPU(struct breakpoint *, cpu_bps[HBP_NUM_MAX]);
    +static LIST_HEAD(task_bps);
    +
    +static struct breakpoint *alloc_breakpoint(struct perf_event *bp)
    +{
    + struct breakpoint *tmp;
    +
    + tmp = kzalloc(sizeof(*tmp), GFP_KERNEL);
    + if (!tmp)
    + return ERR_PTR(-ENOMEM);
    + tmp->bp = bp;
    + tmp->ptrace_bp = is_ptrace_bp(bp);
    + return tmp;
    +}
    +
    +static bool bp_addr_range_overlap(struct perf_event *bp1, struct perf_event *bp2)
    +{
    + __u64 bp1_saddr, bp1_eaddr, bp2_saddr, bp2_eaddr;
    +
    + bp1_saddr = ALIGN_DOWN(bp1->attr.bp_addr, HW_BREAKPOINT_SIZE);
    + bp1_eaddr = ALIGN(bp1->attr.bp_addr + bp1->attr.bp_len, HW_BREAKPOINT_SIZE);
    + bp2_saddr = ALIGN_DOWN(bp2->attr.bp_addr, HW_BREAKPOINT_SIZE);
    + bp2_eaddr = ALIGN(bp2->attr.bp_addr + bp2->attr.bp_len, HW_BREAKPOINT_SIZE);
    +
    + return (bp1_saddr < bp2_eaddr && bp1_eaddr > bp2_saddr);
    +}
    +
    +static bool alternate_infra_bp(struct breakpoint *b, struct perf_event *bp)
    +{
    + return is_ptrace_bp(bp) ? !b->ptrace_bp : b->ptrace_bp;
    +}
    +
    +static bool can_co_exist(struct breakpoint *b, struct perf_event *bp)
    +{
    + return !(alternate_infra_bp(b, bp) && bp_addr_range_overlap(b->bp, bp));
    +}
    +
    +static int task_bps_add(struct perf_event *bp)
    +{
    + struct breakpoint *tmp;
    +
    + tmp = alloc_breakpoint(bp);
    + if (IS_ERR(tmp))
    + return PTR_ERR(tmp);
    +
    + list_add(&tmp->list, &task_bps);
    + return 0;
    +}
    +
    +static void task_bps_remove(struct perf_event *bp)
    +{
    + struct list_head *pos, *q;
    + struct breakpoint *tmp;
    +
    + list_for_each_safe(pos, q, &task_bps) {
    + tmp = list_entry(pos, struct breakpoint, list);
    +
    + if (tmp->bp == bp) {
    + list_del(&tmp->list);
    + kfree(tmp);
    + break;
    + }
    + }
    +}
    +
    +/*
    + * If any task has breakpoint from alternate infrastructure,
    + * return true. Otherwise return false.
    + */
    +static bool all_task_bps_check(struct perf_event *bp)
    +{
    + struct breakpoint *tmp;
    +
    + list_for_each_entry(tmp, &task_bps, list) {
    + if (!can_co_exist(tmp, bp))
    + return true;
    + }
    + return false;
    +}
    +
    +/*
    + * If same task has breakpoint from alternate infrastructure,
    + * return true. Otherwise return false.
    + */
    +static bool same_task_bps_check(struct perf_event *bp)
    +{
    + struct breakpoint *tmp;
    +
    + list_for_each_entry(tmp, &task_bps, list) {
    + if (tmp->bp->hw.target == bp->hw.target &&
    + !can_co_exist(tmp, bp))
    + return true;
    + }
    + return false;
    +}
    +
    +static int cpu_bps_add(struct perf_event *bp)
    +{
    + struct breakpoint **cpu_bp;
    + struct breakpoint *tmp;
    + int i = 0;
    +
    + tmp = alloc_breakpoint(bp);
    + if (IS_ERR(tmp))
    + return PTR_ERR(tmp);
    +
    + cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu);
    + for (i = 0; i < nr_wp_slots(); i++) {
    + if (!cpu_bp[i]) {
    + cpu_bp[i] = tmp;
    + break;
    + }
    + }
    + return 0;
    +}
    +
    +static void cpu_bps_remove(struct perf_event *bp)
    +{
    + struct breakpoint **cpu_bp;
    + int i = 0;
    +
    + cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu);
    + for (i = 0; i < nr_wp_slots(); i++) {
    + if (!cpu_bp[i])
    + continue;
    +
    + if (cpu_bp[i]->bp == bp) {
    + kfree(cpu_bp[i]);
    + cpu_bp[i] = NULL;
    + break;
    + }
    + }
    +}
    +
    +static bool cpu_bps_check(int cpu, struct perf_event *bp)
    +{
    + struct breakpoint **cpu_bp;
    + int i;
    +
    + cpu_bp = per_cpu_ptr(cpu_bps, cpu);
    + for (i = 0; i < nr_wp_slots(); i++) {
    + if (cpu_bp[i] && !can_co_exist(cpu_bp[i], bp))
    + return true;
    + }
    + return false;
    +}
    +
    +static bool all_cpu_bps_check(struct perf_event *bp)
    +{
    + int cpu;
    +
    + for_each_online_cpu(cpu) {
    + if (cpu_bps_check(cpu, bp))
    + return true;
    + }
    + return false;
    +}
    +
    +/*
    + * We don't use any locks to serialize accesses to cpu_bps or task_bps
    + * because are already inside nr_bp_mutex.
    + */
    +int arch_reserve_bp_slot(struct perf_event *bp)
    +{
    + int ret;
    +
    + /* ptrace breakpoint */
    + if (is_ptrace_bp(bp)) {
    + if (all_cpu_bps_check(bp))
    + return -ENOSPC;
    +
    + if (same_task_bps_check(bp))
    + return -ENOSPC;
    +
    + return task_bps_add(bp);
    + }
    +
    + /* perf breakpoint */
    + if (is_kernel_addr(bp->attr.bp_addr))
    + return 0;
    +
    + if (bp->hw.target && bp->cpu == -1) {
    + if (same_task_bps_check(bp))
    + return -ENOSPC;
    +
    + return task_bps_add(bp);
    + } else if (!bp->hw.target && bp->cpu != -1) {
    + if (all_task_bps_check(bp))
    + return -ENOSPC;
    +
    + return cpu_bps_add(bp);
    + }
    +
    + if (same_task_bps_check(bp))
    + return -ENOSPC;
    +
    + ret = cpu_bps_add(bp);
    + if (ret)
    + return ret;
    + ret = task_bps_add(bp);
    + if (ret)
    + cpu_bps_remove(bp);
    +
    + return ret;
    +}
    +
    +void arch_release_bp_slot(struct perf_event *bp)
    +{
    + if (!is_kernel_addr(bp->attr.bp_addr)) {
    + if (bp->hw.target)
    + task_bps_remove(bp);
    + if (bp->cpu != -1)
    + cpu_bps_remove(bp);
    + }
    +}
    +
    /*
    * Perform cleanup of arch-specific counters during unregistration
    * of the perf-event
    diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
    index 3cc8416ec844..b48d7039a015 100644
    --- a/kernel/events/hw_breakpoint.c
    +++ b/kernel/events/hw_breakpoint.c
    @@ -213,6 +213,15 @@ toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
    list_del(&bp->hw.bp_list);
    }

    +__weak int arch_reserve_bp_slot(struct perf_event *bp)
    +{
    + return 0;
    +}
    +
    +__weak void arch_release_bp_slot(struct perf_event *bp)
    +{
    +}
    +
    /*
    * Function to perform processor-specific cleanup during unregistration
    */
    @@ -270,6 +279,7 @@ static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
    struct bp_busy_slots slots = {0};
    enum bp_type_idx type;
    int weight;
    + int ret;

    /* We couldn't initialize breakpoint constraints on boot */
    if (!constraints_initialized)
    @@ -294,6 +304,10 @@ static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
    if (slots.pinned + (!!slots.flexible) > nr_slots[type])
    return -ENOSPC;

    + ret = arch_reserve_bp_slot(bp);
    + if (ret)
    + return ret;
    +
    toggle_bp_slot(bp, true, type, weight);

    return 0;
    @@ -317,6 +331,8 @@ static void __release_bp_slot(struct perf_event *bp, u64 bp_type)
    enum bp_type_idx type;
    int weight;

    + arch_release_bp_slot(bp);
    +
    type = find_slot_idx(bp_type);
    weight = hw_breakpoint_weight(bp);
    toggle_bp_slot(bp, false, type, weight);
    --
    2.21.1
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