linux-kernel - Re: [PATCH v2 1/2] KVM: VMX: Don't advertise EPT switching if EPT itself is not exposed

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Message-ID: <CALMp9eRG902CG4kAq19a3dGRMcQyJ1Le9osLF1QcoqLdyRKdbw@mail.gmail.com>
Date:   Tue, 17 Oct 2017 10:29:13 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2 1/2] KVM: VMX: Don't advertise EPT switching if EPT
 itself is not exposed

Following the same line of reasoning, what if
vmx->nested.nested_vmx_secondary_ctls_high is 0 after clearing
SECONDARY_EXEC_ENABLE_VMFUNC? Does it make sense to report
CPU_BASED_ACTIVATE_SECONDARY_CONTROLS if we don't actually support any
of the secondary controls?

Reviewed-by: Jim Mattson <jmattson@...gle.com>

On Mon, Oct 16, 2017 at 9:03 PM, Wanpeng Li <kernellwp@...il.com> 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>
> ---
> 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 | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index c460b0b..a6861ca 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2842,8 +2842,12 @@ 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;
> +               } else
> +                       vmx->nested.nested_vmx_secondary_ctls_high &=
> +                               ~SECONDARY_EXEC_ENABLE_VMFUNC;
>         }
>
>         /*
> --
> 2.7.4
>