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SubjectRe: [PATCH v2 14/16] powerpc/watchpoint: Don't allow concurrent perf and ptrace events
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Le 01/04/2020 à 08:13, Ravi Bangoria a écrit :
> 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 abc4603c0efe..9d3bd1169591 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 07a6cdea84ed..f813acb0d9f0 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) - 1;
> + 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) - 1;
> +
> + return (bp1_saddr <= bp2_eaddr && bp1_eaddr >= bp2_saddr);

Could avoid the - 1 on bp1_eaddr and bp2_eaddr by doing:

return (bp1_saddr < bp2_eaddr && bp1_eaddr > bp2_saddr);


Christophe

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