linux-kernel - Re: [PATCH v2 0/5] Fix PMU kselftests errors on GNR/SRF/CWF

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Message-ID: <aMIQ6vxYuHA2jVuN@google.com>
Date: Wed, 10 Sep 2025 16:59:38 -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 0/5] Fix PMU kselftests errors on GNR/SRF/CWF

On Fri, Jul 18, 2025, Dapeng Mi wrote:
> This patch series fixes KVM PMU kselftests errors encountered on Granite
> Rapids (GNR), Sierra Forest (SRF) and Clearwater Forest (CWF).
> 
> GNR and SRF starts to support the timed PEBS. Timed PEBS adds a new
> "retired latency" field in basic info group to show the timing info and
> the PERF_CAPABILITIES[17] called "PEBS_TIMING_INFO" bit is added
> to indicated whether timed PEBS is supported. KVM module doesn't need to
> do any specific change to support timed PEBS except a perf change adding
> PERF_CAP_PEBS_TIMING_INFO flag into PERF_CAP_PEBS_MASK[1]. The patch 2/5
> adds timed PEBS support in vmx_pmu_caps_test and fix the error as the
> PEBS caps field mismatch.
> 
> CWF introduces 5 new architectural events (4 level-1 topdown metrics
> events and LBR inserts event). The patch 3/5 adds support for these 5
> arch-events and fixes the error that caused by mismatch between HW real
> supported arch-events number with NR_INTEL_ARCH_EVENTS.
> 
> On Intel Atom platforms, the PMU events "Instruction Retired" or
> "Branch Instruction Retired" may be overcounted for some certain
> instructions, like FAR CALL/JMP, RETF, IRET, VMENTRY/VMEXIT/VMPTRLD
> and complex SGX/SMX/CSTATE instructions/flows[2].
> 
> In details, for the Atom platforms before Sierra Forest (including
> Sierra Forest), Both 2 events "Instruction Retired" and
> "Branch Instruction Retired" would be overcounted on these certain
> instructions, but for Clearwater Forest only "Instruction Retired" event
> is overcounted on these instructions.
> 
> As this overcount issue, pmu_counters_test and pmu_event_filter_test
> would fail on the precise event count validation for these 2 events on
> Atom platforms.
> 
> To work around this Atom platform overcount issue, Patches 4-5/5 looses
> the precise count validation separately for pmu_counters_test and
> pmu_event_filter_test.
> 
> BTW, this patch series doesn't depend on the mediated vPMU support.
> 
> Changes:
>   * Add error fix for vmx_pmu_caps_test on GNR/SRF (patch 2/5).
>   * Opportunistically fix a typo (patch 1/5).
> 
> Tests:
>   * PMU kselftests (pmu_counters_test/pmu_event_filter_test/
>     vmx_pmu_caps_test) passed on Intel SPR/GNR/SRF/CWF platforms.
> 
> History:
>   * v1: https://lore.kernel.org/all/20250712172522.187414-1-dapeng1.mi@linux.intel.com/
> 
> Ref:
>   [1] https://lore.kernel.org/all/20250717090302.11316-1-dapeng1.mi@linux.intel.com/
>   [2] https://edc.intel.com/content/www/us/en/design/products-and-solutions/processors-and-chipsets/sierra-forest/xeon-6700-series-processor-with-e-cores-specification-update/errata-details
> 
> Dapeng Mi (4):
>   KVM: x86/pmu: Correct typo "_COUTNERS" to "_COUNTERS"
>   KVM: selftests: Add timing_info bit support in vmx_pmu_caps_test
>   KVM: Selftests: Validate more arch-events in pmu_counters_test
>   KVM: selftests: Relax branches event count check for event_filter test
> 
> dongsheng (1):
>   KVM: selftests: Relax precise event count validation as overcount
>     issue

Overall looks good, I just want to take a more infrastructure-oriented approach
for the errata.  I'll post a v3 tomorrow.  All coding is done and the tests pass,
but I want to take a second look with fresh eyes before posting it :-)