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

From: Sean Christopherson <[email-masked]>
Date: Mon, 29 Dec 2025 15:57:21 -0800

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 <[email-masked]>
> > Tested-by: Xudong Hao <[email-masked]>
> > Signed-off-by: Sean Christopherson <[email-masked]>
> > ---
> >  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
> 
>