linux-kernel - Re: [PATCH] KVM: x86: Check the right feature bit for MSR_KVM_ASYNC_PF

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Message-ID: <YPmopoGY4hwuVHAp@google.com>
Date:   Thu, 22 Jul 2021 17:19:34 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Oliver Upton <oupton@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Check the right feature bit for
 MSR_KVM_ASYNC_PF_ACK access

On Thu, Jul 22, 2021, Vitaly Kuznetsov wrote:
> MSR_KVM_ASYNC_PF_ACK MSR is part of interrupt based asynchronous page fault
> interface and not the original (deprecated) KVM_FEATURE_ASYNC_PF. This is
> stated in Documentation/virt/kvm/msr.rst.
> 
> Fixes: 66570e966dd9 ("kvm: x86: only provide PV features if enabled in guest's CPUID")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.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 d715ae9f9108..88ff7a1af198 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3406,7 +3406,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  			return 1;
>  		break;
>  	case MSR_KVM_ASYNC_PF_ACK:
> -		if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF))
> +		if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF_INT))

Do we want to require both, or do we want to let userspace be stupid?

>  			return 1;
>  		if (data & 0x1) {
>  			vcpu->arch.apf.pageready_pending = false;
> @@ -3745,7 +3745,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		msr_info->data = vcpu->arch.apf.msr_int_val;
>  		break;
>  	case MSR_KVM_ASYNC_PF_ACK:
> -		if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF))
> +		if (!guest_pv_has(vcpu, KVM_FEATURE_ASYNC_PF_INT))
>  			return 1;
>  
>  		msr_info->data = 0;
> -- 
> 2.31.1
>