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: <aVMVYY_WkNClfXuj@google.com>
Date: Mon, 29 Dec 2025 15:57:21 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: 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>, 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 Thu, Dec 25, 2025, Dapeng Mi wrote:
> 
> 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.

Gah, right you are.  I overlooked it because it didn't conflict on a rebase, and
I once again forgot to test on a hybrid PMU, grr.

Thanks!

> 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
> 
>