linux-kernel - Re: [PATCH v3 1/2] KVM: nVMX: Fix EPT switching advertising

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Message-ID: <1cad7936-cbf3-2723-9892-60e66528a2d1@redhat.com>
Date:   Wed, 18 Oct 2017 11:31:11 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v3 1/2] KVM: nVMX: Fix EPT switching advertising

On 18.10.2017 03:42, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> 
> I can use vmxcap tool to observe "EPTP Switching   yes" even if EPT is not 
> exposed to L1.
> 
> EPT switching is advertised unconditionally since it is emulated, however, 
> it can be treated as an extended feature for EPT and it should not be 
> advertised if EPT itself is not exposed. This patch fixes it.
> 
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Cc: Jim Mattson <jmattson@...gle.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
> v2 -> v3:
>  * it is legal for the IA32_VMX_VMFUNC MSR to report all-zero
> v1 -> v2:
>  * don't advertise "EPT VM Functions" in secondary processor-based VM-execution 
>    controls if we don't actually support any VM Functions.
> 
>  arch/x86/kvm/vmx.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index c460b0b..3644540 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2842,8 +2842,9 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
>  		 * Advertise EPTP switching unconditionally
>  		 * since we emulate it
>  		 */
> -		vmx->nested.nested_vmx_vmfunc_controls =
> -			VMX_VMFUNC_EPTP_SWITCHING;
> +		if (enable_ept)
> +			vmx->nested.nested_vmx_vmfunc_controls =
> +				VMX_VMFUNC_EPTP_SWITCHING;
>  	}
>  
>  	/*
> 

I think we talked about how that cannot happen. But you observe it, so
it seems to happen :)

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 

Thanks,

David