linux-kernel - Re: [PATCH 1/3] KVM: x86/pmu: Accept 0 for absent PMU MSRs when host-initiated if !enable

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Date:   Wed, 1 Jun 2022 12:22:56 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Like Xu <like.xu.linux@...il.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] KVM: x86/pmu: Accept 0 for absent PMU MSRs when
 host-initiated if !enable_pmu

On 6/1/22 05:19, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
> 
> Whenever an MSR is part of KVM_GET_MSR_INDEX_LIST, as is the case for
> MSR_K7_EVNTSEL0 or MSR_F15H_PERF_CTL0, it has to be always retrievable
> and settable with KVM_GET_MSR and KVM_SET_MSR.
> 
> Accept a zero value for these MSRs to obey the contract.
> 
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
> Note, if !enable_pmu, it is easy to reproduce and verify it with selftest.
> 
>   arch/x86/kvm/pmu.c     |  8 ++++++++
>   arch/x86/kvm/svm/pmu.c | 11 ++++++++++-
>   2 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> index 7a74691de223..3575a3746bf9 100644
> --- a/arch/x86/kvm/pmu.c
> +++ b/arch/x86/kvm/pmu.c
> @@ -439,11 +439,19 @@ static void kvm_pmu_mark_pmc_in_use(struct kvm_vcpu *vcpu, u32 msr)
>   
>   int kvm_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   {
> +	if (msr_info->host_initiated && !vcpu->kvm->arch.enable_pmu) {
> +		msr_info->data = 0;
> +		return 0;
> +	}
> +
>   	return static_call(kvm_x86_pmu_get_msr)(vcpu, msr_info);
>   }
>   
>   int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   {
> +	if (msr_info->host_initiated && !vcpu->kvm->arch.enable_pmu)
> +		return !!msr_info->data;
> +
>   	kvm_pmu_mark_pmc_in_use(vcpu, msr_info->index);
>   	return static_call(kvm_x86_pmu_set_msr)(vcpu, msr_info);
>   }
> diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
> index 256244b8f89c..fe520b2649b5 100644
> --- a/arch/x86/kvm/svm/pmu.c
> +++ b/arch/x86/kvm/svm/pmu.c
> @@ -182,7 +182,16 @@ static struct kvm_pmc *amd_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
>   static bool amd_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr, bool host_initiated)
>   {
>   	/* All MSRs refer to exactly one PMC, so msr_idx_to_pmc is enough.  */
> -	return false;
> +	if (!host_initiated)
> +		return false;
> +
> +	switch (msr) {
> +	case MSR_K7_EVNTSEL0 ... MSR_K7_PERFCTR3:
> +	case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5:
> +		return true;
> +	default:
> +		return false;
> +	}
>   }
>   
>   static struct kvm_pmc *amd_msr_idx_to_pmc(struct kvm_vcpu *vcpu, u32 msr)

Queued all three, thanks.

Paolo