linux-kernel - Re: [PATCH] x86/kvm/nVMX: don't skip emulated instruction twice when vmptr address is not backed

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Message-ID: <20190109185147.3d9ecec4.cohuck@redhat.com>
Date:   Wed, 9 Jan 2019 18:51:47 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, Andrew Jones <drjones@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH] x86/kvm/nVMX: don't skip emulated instruction twice
 when vmptr address is not backed

On Wed,  9 Jan 2019 18:22:56 +0100
Vitaly Kuznetsov <vkuznets@...hat.com> wrote:

> Since commit 09abb5e3e5e50 ("KVM: nVMX: call kvm_skip_emulated_instruction
> in nested_vmx_{fail,succeed}") nested_vmx_failValid() results in
> kvm_skip_emulated_instruction() so doing it again in handle_vmptrld() when
> vmptr address is not backed is wrong, we end up advancing RIP twice.
> 
> Fixes: fca91f6d60b6e ("kvm: nVMX: Set VM instruction error for VMPTRLD of unbacked page")
> Reported-by: Cornelia Huck <cohuck@...hat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 3170e291215d..2616bd2c7f2c 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4540,9 +4540,8 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
>  			 * given physical address won't match the required
>  			 * VMCS12_REVISION identifier.
>  			 */
> -			nested_vmx_failValid(vcpu,
> +			return nested_vmx_failValid(vcpu,
>  				VMXERR_VMPTRLD_INCORRECT_VMCS_REVISION_ID);
> -			return kvm_skip_emulated_instruction(vcpu);
>  		}
>  		new_vmcs12 = kmap(page);
>  		if (new_vmcs12->hdr.revision_id != VMCS12_REVISION ||

Not that I would be a nested vmx expert, but this looks correct.

Reviewed-by: Cornelia Huck <cohuck@...hat.com>