linux-kernel - Re: [PATCH v3 1/4] KVM: SVM: Inject #GP on guest MSR_TSC

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Message-ID: <87mttlfn1w.fsf@vitty.brq.redhat.com>
Date:   Mon, 26 Apr 2021 10:49:15 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Reiji Watanabe <reijiw@...gle.com>
Subject: Re: [PATCH v3 1/4] KVM: SVM: Inject #GP on guest MSR_TSC_AUX
 accesses if RDTSCP unsupported

Sean Christopherson <seanjc@...gle.com> writes:

> Inject #GP on guest accesses to MSR_TSC_AUX if RDTSCP is unsupported in
> the guest's CPUID model.
>
> Fixes: 46896c73c1a4 ("KVM: svm: add support for RDTSCP")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/svm/svm.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index cd8c333ed2dc..9ed9c7bd7cfd 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2674,6 +2674,9 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_TSC_AUX:
>  		if (!boot_cpu_has(X86_FEATURE_RDTSCP))
>  			return 1;
> +		if (!msr_info->host_initiated &&
> +		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
> +			return 1;

Super-nit: a blank like before and after the condition would make this
consistent with the hunk you add to svm_set_msr() below.

>  		msr_info->data = svm->tsc_aux;
>  		break;
>  	/*
> @@ -2892,6 +2895,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
>  		if (!boot_cpu_has(X86_FEATURE_RDTSCP))
>  			return 1;
>  
> +		if (!msr->host_initiated &&
> +		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
> +			return 1;
> +
>  		/*
>  		 * This is rare, so we update the MSR here instead of using
>  		 * direct_access_msrs.  Doing that would require a rdmsr in

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly