linux-kernel - Re: [PATCH v6 15/44] KVM: x86/pmu: Snapshot host (i.e. perf's) reported PMU capabilities

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Message-ID: <43d1cde6-2277-4f3c-8e7d-59e6edb2228a@linux.intel.com>
Date: Thu, 25 Dec 2025 14:26:56 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oupton@...nel.org>, Tianrui Zhao <zhaotianrui@...ngson.cn>,
 Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
 Anup Patel <anup@...infault.org>, Paul Walmsley <pjw@...nel.org>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Xin Li <xin@...or.com>, "H. Peter Anvin" <hpa@...or.com>,
 Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
 kvm@...r.kernel.org, loongarch@...ts.linux.dev,
 kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 Mingwei Zhang <mizhang@...gle.com>, Xudong Hao <xudong.hao@...el.com>,
 Sandipan Das <sandipan.das@....com>,
 Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
 Manali Shukla <manali.shukla@....com>, Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v6 15/44] KVM: x86/pmu: Snapshot host (i.e. perf's)
 reported PMU capabilities

On 12/6/2025 8:16 AM, Sean Christopherson wrote:
> Take a snapshot of the unadulterated PMU capabilities provided by perf so
> that KVM can compare guest vPMU capabilities against hardware capabilities
> when determining whether or not to intercept PMU MSRs (and RDPMC).
>
> Reviewed-by: Sandipan Das <sandipan.das@....com>
> Tested-by: Xudong Hao <xudong.hao@...el.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/pmu.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 487ad19a236e..7c219305b61d 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -108,6 +108,8 @@ void kvm_init_pmu_capability(const struct kvm_pmu_ops *pmu_ops)
>  	bool is_intel = boot_cpu_data.x86_vendor == X86_VENDOR_INTEL;
>  	int min_nr_gp_ctrs = pmu_ops->MIN_NR_GP_COUNTERS;
>  
> +	perf_get_x86_pmu_capability(&kvm_host_pmu);
> +
>  	/*
>  	 * Hybrid PMUs don't play nice with virtualization without careful
>  	 * configuration by userspace, and KVM's APIs for reporting supported

Hi Sean,

It looks a merging error here. We don't need this patch.

The original patch "51f34b1 ("KVM: x86/pmu: Snapshot host (i.e. perf's)
reported PMU capabilities")" had been merged into upstream and subsequently
we submitted a new patch "034417c1439a ("KVM: x86/pmu: Don't try to get
perf capabilities for hybrid CPUs")" to fix the warning introduced from
previous patch  "51f34b1 ("KVM: x86/pmu: Snapshot host (i.e. perf's)
reported PMU capabilities")". Thanks.

-Dapeng Mi