linux-kernel - Re: [PATCH V3 2/2] perf/x86: Reset the dirty counter to prevent the leak for an RDPMC task

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Date:   Wed, 14 Apr 2021 22:51:09 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Kan Liang <kan.liang@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>, luto@...capital.net,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH V3 2/2] perf/x86: Reset the dirty counter to prevent the
 leak for an RDPMC task

Hi Kan,

On Wed, Apr 14, 2021 at 4:04 AM <kan.liang@...ux.intel.com> wrote:
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index dd9f3c2..0d4a1a3 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -1585,6 +1585,8 @@ static void x86_pmu_del(struct perf_event *event, int flags)
>         if (cpuc->txn_flags & PERF_PMU_TXN_ADD)
>                 goto do_del;
>
> +       __set_bit(event->hw.idx, cpuc->dirty);
> +
>         /*
>          * Not a TXN, therefore cleanup properly.
>          */
> @@ -2304,12 +2306,46 @@ static int x86_pmu_event_init(struct perf_event *event)
>         return err;
>  }
>
> +void x86_pmu_clear_dirty_counters(void)
> +{
> +       struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> +       int i;
> +
> +       if (bitmap_empty(cpuc->dirty, X86_PMC_IDX_MAX))
> +               return;

Maybe you can check it after clearing assigned counters.

Thanks,
Namhyung

> +
> +        /* Don't need to clear the assigned counter. */
> +       for (i = 0; i < cpuc->n_events; i++)
> +               __clear_bit(cpuc->assign[i], cpuc->dirty);
> +
> +       for_each_set_bit(i, cpuc->dirty, X86_PMC_IDX_MAX) {
> +               /* Metrics and fake events don't have corresponding HW counters. */
> +               if (is_metric_idx(i) || (i == INTEL_PMC_IDX_FIXED_VLBR))
> +                       continue;
> +               else if (i >= INTEL_PMC_IDX_FIXED)
> +                       wrmsrl(MSR_ARCH_PERFMON_FIXED_CTR0 + (i - INTEL_PMC_IDX_FIXED), 0);
> +               else
> +                       wrmsrl(x86_pmu_event_addr(i), 0);
> +       }
> +
> +       bitmap_zero(cpuc->dirty, X86_PMC_IDX_MAX);
> +}