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

[Liang, Kan]

On 4/14/2021 9:51 AM, Namhyung Kim wrote:
> Hi Kan,
>
> On Wed, Apr 14, 2021 at 4:04 AM <kan.liang@xxxxxxxxxxxxxxx> 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.

It should be very likely that the cpuc->dirty is non-empty.
Move it after the clearing can skip the for_each_set_bit() and 
bitmap_zero().
OK. I will change it in V4.

Thanks,
Kan