linux-kernel - Re: [PATCH 1/3] KVM: x86: Refresh PMU after writes to MSR_IA32_PERF

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Message-ID: <cb631fe5-103d-30f5-d800-4748f4ea41fa@gmail.com>
Date:   Wed, 3 Aug 2022 20:29:43 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 1/3] KVM: x86: Refresh PMU after writes to
 MSR_IA32_PERF_CAPABILITIES

On 28/7/2022 7:34 am, Sean Christopherson wrote:
> Refresh the PMU if userspace modifies MSR_IA32_PERF_CAPABILITIES.  KVM
> consumes the vCPU's PERF_CAPABILITIES when enumerating PEBS support, but
> relies on CPUID updates to refresh the PMU.  I.e. KVM will do the wrong
> thing if userspace stuffs PERF_CAPABILITIES _after_ setting guest CPUID.
> 
> Opportunistically fix a curly-brace indentation.
> 
> Fixes: c59a1f106f5c ("KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS")

Shouldn't it be: Fixes: 27461da31089 ("KVM: x86/pmu: Support full width counting") ?

Now, all the dots have been connected. As punishment, I'd like to cook this 
patch set more
with trackable tests so that you have more time for other things that are not 
housekeeping.

Thank you, Sean.

> Cc: Like Xu <like.xu.linux@...il.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/x86.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5366f884e9a7..362c538285db 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3543,9 +3543,9 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   			return 1;
>   
>   		vcpu->arch.perf_capabilities = data;
> -
> +		kvm_pmu_refresh(vcpu);
>   		return 0;
> -		}
> +	}
>   	case MSR_EFER:
>   		return set_efer(vcpu, msr_info);
>   	case MSR_K7_HWCR: