linux-kernel - Re: [PATCH] KVM: nVMX: fix AD condition when handling EPT violation

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Message-ID: <b64213c7-42d9-f42d-3bf1-9660c6ef426a@redhat.com>
Date:   Fri, 14 Apr 2017 13:10:47 +0800
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: fix AD condition when handling EPT violation



On 14/04/2017 00:39, Radim Krčmář wrote:
> I have introduced this bug when applying and simplifying Paolo's patch
> as we agreed on the list.  The original was "x &= ~y; if (z) x |= y;".
> 
> Here is the story of a bad workflow:
> 
>   A maintainer was already testing with the intended change, but it was
>   applied only to a testing repo on a different machine.  When the time
>   to push tested patches to kvm/next came, he realized that this change
>   was missing and quickly added it to the maintenance repo, didn't test
>   again (because the change is trivial, right), and pushed the world to
>   fire.
> 
> Fixes: ae1e2d1082ae ("kvm: nVMX: support EPT accessed/dirty bits")
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  arch/x86/kvm/vmx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index cfdb0d9389d1..837f6dd1ae9c 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6221,7 +6221,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
>  		 * page table accesses are reads or writes.
>  		 */
>  		u64 eptp = nested_ept_get_cr3(vcpu);
> -		if (eptp & VMX_EPT_AD_ENABLE_BIT)
> +		if (!(eptp & VMX_EPT_AD_ENABLE_BIT))
>  			exit_qualification &= ~EPT_VIOLATION_ACC_WRITE;
>  	}
>  
> 

I have done this as well, so you're forgiven. :)

More important: did kvm-unit-test catch the bug?

Paolo