Re: [PATCH 5.4] KVM: x86/svm: Account for family 17h event renumberings in amd_pmc_perf_hw_id

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On Tue, May 10, 2022 at 4:38 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Tue, May 10, 2022 at 01:37:08PM +0200, Greg KH wrote:
> > On Mon, May 09, 2022 at 01:41:20PM +0200, Paolo Bonzini wrote:
> > > On 5/8/22 18:54, Kyle Huey wrote:
> > > > From: Kyle Huey <me@xxxxxxxxxxxx>
> > > >
> > > > commit 5eb849322d7f7ae9d5c587c7bc3b4f7c6872cd2f upstream
> > > >
> > > > Zen renumbered some of the performance counters that correspond to the
> > > > well known events in perf_hw_id. This code in KVM was never updated for
> > > > that, so guest that attempt to use counters on Zen that correspond to the
> > > > pre-Zen perf_hw_id values will silently receive the wrong values.
> > > >
> > > > This has been observed in the wild with rr[0] when running in Zen 3
> > > > guests. rr uses the retired conditional branch counter 00d1 which is
> > > > incorrectly recognized by KVM as PERF_COUNT_HW_STALLED_CYCLES_BACKEND.
> > > >
> > > > [0] https://rr-project.org/
> > > >
> > > > Signed-off-by: Kyle Huey <me@xxxxxxxxxxxx>
> > > > Message-Id: <20220503050136.86298-1-khuey@xxxxxxxxxxxx>
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > [Check guest family, not host. - Paolo]
> > > > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > > > [Backport to 5.4: adjusted context]
> > > > Signed-off-by: Kyle Huey <me@xxxxxxxxxxxx>
> > > > ---
> > > >   arch/x86/kvm/pmu_amd.c | 28 +++++++++++++++++++++++++---
> > > >   1 file changed, 25 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/arch/x86/kvm/pmu_amd.c b/arch/x86/kvm/pmu_amd.c
> > > > index 6bc656abbe66..3ccfd1abcbad 100644
> > > > --- a/arch/x86/kvm/pmu_amd.c
> > > > +++ b/arch/x86/kvm/pmu_amd.c
> > > > @@ -44,6 +44,22 @@ static struct kvm_event_hw_type_mapping amd_event_mapping[] = {
> > > >           [7] = { 0xd1, 0x00, PERF_COUNT_HW_STALLED_CYCLES_BACKEND },
> > > >   };
> > > > +/* duplicated from amd_f17h_perfmon_event_map. */
> > > > +static struct kvm_event_hw_type_mapping amd_f17h_event_mapping[] = {
> > > > + [0] = { 0x76, 0x00, PERF_COUNT_HW_CPU_CYCLES },
> > > > + [1] = { 0xc0, 0x00, PERF_COUNT_HW_INSTRUCTIONS },
> > > > + [2] = { 0x60, 0xff, PERF_COUNT_HW_CACHE_REFERENCES },
> > > > + [3] = { 0x64, 0x09, PERF_COUNT_HW_CACHE_MISSES },
> > > > + [4] = { 0xc2, 0x00, PERF_COUNT_HW_BRANCH_INSTRUCTIONS },
> > > > + [5] = { 0xc3, 0x00, PERF_COUNT_HW_BRANCH_MISSES },
> > > > + [6] = { 0x87, 0x02, PERF_COUNT_HW_STALLED_CYCLES_FRONTEND },
> > > > + [7] = { 0x87, 0x01, PERF_COUNT_HW_STALLED_CYCLES_BACKEND },
> > > > +};
> > > > +
> > > > +/* amd_pmc_perf_hw_id depends on these being the same size */
> > > > +static_assert(ARRAY_SIZE(amd_event_mapping) ==
> > > > +      ARRAY_SIZE(amd_f17h_event_mapping));
> > > > +
> > > >   static unsigned int get_msr_base(struct kvm_pmu *pmu, enum pmu_type type)
> > > >   {
> > > >           struct kvm_vcpu *vcpu = pmu_to_vcpu(pmu);
> > > > @@ -130,17 +146,23 @@ static unsigned amd_find_arch_event(struct kvm_pmu *pmu,
> > > >                                       u8 event_select,
> > > >                                       u8 unit_mask)
> > > >   {
> > > > + struct kvm_event_hw_type_mapping *event_mapping;
> > > >           int i;
> > > > + if (guest_cpuid_family(pmc->vcpu) >= 0x17)
> > > > +         event_mapping = amd_f17h_event_mapping;
> > > > + else
> > > > +         event_mapping = amd_event_mapping;
> > > > +
> > > >           for (i = 0; i < ARRAY_SIZE(amd_event_mapping); i++)
> > > > -         if (amd_event_mapping[i].eventsel == event_select
> > > > -             && amd_event_mapping[i].unit_mask == unit_mask)
> > > > +         if (event_mapping[i].eventsel == event_select
> > > > +             && event_mapping[i].unit_mask == unit_mask)
> > > >                           break;
> > > >           if (i == ARRAY_SIZE(amd_event_mapping))
> > > >                   return PERF_COUNT_HW_MAX;
> > > > - return amd_event_mapping[i].event_type;
> > > > + return event_mapping[i].event_type;
> > > >   }
> > > >   /* return PERF_COUNT_HW_MAX as AMD doesn't have fixed events */
> > >
> > > Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > >
> > > Thanks,
> > >
> > > Paolo
> > >
> >
> > Wait, how was this tested?
> >
> > It breaks the build:
> >
> > arch/x86/kvm/pmu_amd.c: In function ‘amd_find_arch_event’:
> > arch/x86/kvm/pmu_amd.c:152:32: error: ‘pmc’ undeclared (first use in this function); did you mean ‘pmu’?
> >   152 |         if (guest_cpuid_family(pmc->vcpu) >= 0x17)
> >       |                                ^~~
> >       |                                pmu
> >
> >
> > I'll do the obvious fixup, but this is odd.  Always at least test-build
> > your changes...
>
> Hm, no, I don't know what the correct fix is here.  I'll wait for a
> fixed up (and tested) patch to be resubmited please.
>
> thanks,
>
> greg k-h

Sorry, I tested an earlier version without the guest_cpuid_family fix
that Paolo made when he committed my patch, and of course that's the
hang up here. I'll get this fixed up for you.

- Kyle




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