linux-kernel - Re: [Patch v5 06/18] x86: pmu: Add asserts to warn inconsistent fixed events and counters

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Message-ID: <CALMp9eT2pc0qDaySuyNcHr5+tO4gfvrqmYo=a3Ay-0=rfhiksg@mail.gmail.com>
Date: Mon, 26 Aug 2024 11:36:49 -0700
From: Jim Mattson <jmattson@...gle.com>
To: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
Cc: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Mingwei Zhang <mizhang@...gle.com>, 
	Xiong Zhang <xiong.y.zhang@...el.com>, Zhenyu Wang <zhenyuw@...ux.intel.com>, 
	Like Xu <like.xu.linux@...il.com>, Jinrong Liang <cloudliang@...cent.com>, 
	Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [Patch v5 06/18] x86: pmu: Add asserts to warn inconsistent fixed
 events and counters

On Sun, Aug 25, 2024 at 11:56 PM Mi, Dapeng <dapeng1.mi@...ux.intel.com> wrote:
>
>
> On 8/23/2024 2:22 AM, Jim Mattson wrote:
> > On Tue, Jul 2, 2024 at 7:12 PM Dapeng Mi <dapeng1.mi@...ux.intel.com> wrote:
> >> Current PMU code deosn't check whether PMU fixed counter number is
> >> larger than pre-defined fixed events. If so, it would cause memory
> >> access out of range.
> >>
> >> So add assert to warn this invalid case.
> >>
> >> Reviewed-by: Mingwei Zhang <mizhang@...gle.com>
> >> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> >> ---
> >>  x86/pmu.c | 10 ++++++++--
> >>  1 file changed, 8 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/x86/pmu.c b/x86/pmu.c
> >> index b4de2680..3e0bf3a2 100644
> >> --- a/x86/pmu.c
> >> +++ b/x86/pmu.c
> >> @@ -113,8 +113,12 @@ static struct pmu_event* get_counter_event(pmu_counter_t *cnt)
> >>                 for (i = 0; i < gp_events_size; i++)
> >>                         if (gp_events[i].unit_sel == (cnt->config & 0xffff))
> >>                                 return &gp_events[i];
> >> -       } else
> >> -               return &fixed_events[cnt->ctr - MSR_CORE_PERF_FIXED_CTR0];
> >> +       } else {
> >> +               unsigned int idx = cnt->ctr - MSR_CORE_PERF_FIXED_CTR0;
> >> +
> >> +               assert(idx < ARRAY_SIZE(fixed_events));
> > Won't this assertion result in a failure on bare metal, for CPUs
> > supporting fixed counter 3?
>
> Yes, this is intended use. Currently KVM vPMU still doesn't support fixed
> counter 3. If it's supported in KVM vPMU one day but forget to add
> corresponding support in this pmu test, this assert would remind this.

These tests are supposed to run (and pass) on bare metal. Hence, they
should not be dependent on a non-architectural quirk of the KVM
implementation.

Perhaps a warning would serve as a reminder?

>
> >
> >> +               return &fixed_events[idx];
> >> +       }
> >>
> >>         return (void*)0;
> >>  }
> >> @@ -740,6 +744,8 @@ int main(int ac, char **av)
> >>         printf("Fixed counters:      %d\n", pmu.nr_fixed_counters);
> >>         printf("Fixed counter width: %d\n", pmu.fixed_counter_width);
> >>
> >> +       assert(pmu.nr_fixed_counters <= ARRAY_SIZE(fixed_events));
> >> +
> > And this one as well?
> >
> >>         apic_write(APIC_LVTPC, PMI_VECTOR);
> >>
> >>         check_counters();
> >> --
> >> 2.40.1
> >>