linux-kernel - Re: [PATCH v3 5/5] KVM: selftests: Handle Intel Atom errata that leads to PMU event overcount

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Message-ID: <aM1uzfweXxoaaLpt@google.com>
Date: Fri, 19 Sep 2025 07:55:09 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Yi Lai <yi1.lai@...el.com>, dongsheng <dongsheng.x.zhang@...el.com>
Subject: Re: [PATCH v3 5/5] KVM: selftests: Handle Intel Atom errata that
 leads to PMU event overcount

On Fri, Sep 19, 2025, Dapeng Mi wrote:
> 
> On 9/19/2025 8:45 AM, Sean Christopherson wrote:
> > diff --git a/tools/testing/selftests/kvm/x86/pmu_counters_test.c b/tools/testing/selftests/kvm/x86/pmu_counters_test.c
> > index baa7b8a2d459..acb5a5c37296 100644
> > --- a/tools/testing/selftests/kvm/x86/pmu_counters_test.c
> > +++ b/tools/testing/selftests/kvm/x86/pmu_counters_test.c
> > @@ -163,10 +163,18 @@ static void guest_assert_event_count(uint8_t idx, uint32_t pmc, uint32_t pmc_msr
> >  
> >  	switch (idx) {
> >  	case INTEL_ARCH_INSTRUCTIONS_RETIRED_INDEX:
> > -		GUEST_ASSERT_EQ(count, NUM_INSNS_RETIRED);
> > +		/* Relax precise count check due to VM-EXIT/VM-ENTRY overcount issue */
> > +		if (this_pmu_has_errata(INSTRUCTIONS_RETIRED_OVERCOUNT))
> 
> The pmu_errata_mask is a bitmap, so the argument should be
> BIT_ULL(INSTRUCTIONS_RETIRED_OVERCOUNT) instead of
> INSTRUCTIONS_RETIRED_OVERCOUNT?

Gah, I just forgot to use BIT_ULL() in this_pmu_has_errata().

diff --git a/tools/testing/selftests/kvm/include/x86/pmu.h b/tools/testing/selftests/kvm/include/x86/pmu.h
index 25d2b476daf4..308c9f6f0d57 100644
--- a/tools/testing/selftests/kvm/include/x86/pmu.h
+++ b/tools/testing/selftests/kvm/include/x86/pmu.h
@@ -115,7 +115,7 @@ void kvm_init_pmu_errata(void);
 
 static inline bool this_pmu_has_errata(enum pmu_errata errata)
 {
-       return pmu_errata_mask & errata;
+       return pmu_errata_mask & BIT_ULL(errata);
 }
 
 #endif /* SELFTEST_KVM_PMU_H */


> 
> Or better, directly define INSTRUCTIONS_RETIRED_OVERCOUNT as a bitmap, like
> this.
> 
> diff --git a/tools/testing/selftests/kvm/include/x86/pmu.h
> b/tools/testing/selftests/kvm/include/x86/pmu.h
> index 25d2b476daf4..9af448129597 100644
> --- a/tools/testing/selftests/kvm/include/x86/pmu.h
> +++ b/tools/testing/selftests/kvm/include/x86/pmu.h
> @@ -106,8 +106,8 @@ extern const uint64_t intel_pmu_arch_events[];
>  extern const uint64_t amd_pmu_zen_events[];
> 
>  enum pmu_errata {
> -       INSTRUCTIONS_RETIRED_OVERCOUNT,
> -       BRANCHES_RETIRED_OVERCOUNT,
> +       INSTRUCTIONS_RETIRED_OVERCOUNT = (1 << 0),
> +       BRANCHES_RETIRED_OVERCOUNT     = (1 << 1),

I want to utilize the auto-incrementing behavior of enums, without having to
resort to double-defines or anything.