linux-kernel - Re: [PATCH v2 5/5] KVM: selftests: Relax branches event count check for event

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Message-ID: <aMIPK6ZeTi3_iLzc@google.com>
Date: Wed, 10 Sep 2025 16:52:11 -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, 
	Jim Mattson <jmattson@...gle.com>, Mingwei Zhang <mizhang@...gle.com>, 
	Zide Chen <zide.chen@...el.com>, Das Sandipan <Sandipan.Das@....com>, 
	Shukla Manali <Manali.Shukla@....com>, Yi Lai <yi1.lai@...el.com>, 
	Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [PATCH v2 5/5] KVM: selftests: Relax branches event count check
 for event_filter test

On Fri, Jul 18, 2025, Dapeng Mi wrote:
> As the branches event overcount issue on Atom platforms, once there are
> VM-Exits triggered (external interrupts) in the guest loop, the measured
> branch event count could be larger than NUM_BRANCHES, this would lead to
> the pmu_event_filter_test print warning to info the measured branches
> event count is mismatched with expected number (NUM_BRANCHES).
> 
> To eliminate this warning, relax the branches event count check on the
> Atom platform which have the branches event overcount issue.
> 
> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> Tested-by: Yi Lai <yi1.lai@...el.com>
> ---

This can be squashed with the previous patch, "workaround errata" is a single
logical change as far as I'm concerned.

>  tools/testing/selftests/kvm/x86/pmu_event_filter_test.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c b/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
> index c15513cd74d1..9c1a92f05786 100644
> --- a/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
> +++ b/tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
> @@ -60,6 +60,8 @@ struct {
>  	uint64_t instructions_retired;
>  } pmc_results;
>  
> +static uint8_t inst_overcount_flags;
> +
>  /*
>   * If we encounter a #GP during the guest PMU sanity check, then the guest
>   * PMU is not functional. Inform the hypervisor via GUEST_SYNC(0).
> @@ -214,8 +216,10 @@ static void remove_event(struct __kvm_pmu_event_filter *f, uint64_t event)
>  do {											\
>  	uint64_t br = pmc_results.branches_retired;					\
>  	uint64_t ir = pmc_results.instructions_retired;					\
> +	bool br_matched = inst_overcount_flags & BR_RETIRED_OVERCOUNT ?			\
> +			  br >= NUM_BRANCHES : br == NUM_BRANCHES;			\
>  											\
> -	if (br && br != NUM_BRANCHES)							\
> +	if (br && !br_matched)								\
>  		pr_info("%s: Branch instructions retired = %lu (expected %u)\n",	\
>  			__func__, br, NUM_BRANCHES);					\
>  	TEST_ASSERT(br, "%s: Branch instructions retired = %lu (expected > 0)",		\
> @@ -850,6 +854,9 @@ int main(int argc, char *argv[])
>  	if (use_amd_pmu())
>  		test_amd_deny_list(vcpu);
>  
> +	if (use_intel_pmu())

Checking for an Intel CPU should be done by the library.