linux-kernel - Re: [PATCH RESEND] KVM: nVMX: mask unrestricted

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Message-ID: <20150317184315.GP31340@tesla.redhat.com>
Date:	Tue, 17 Mar 2015 19:43:15 +0100
From:	Kashyap Chamarthy <kchamart@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Paolo Bonzini <pbonzini@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH RESEND] KVM: nVMX: mask unrestricted_guest if disabled on
 L0

On Tue, Mar 17, 2015 at 02:02:32PM +0100, Radim Krčmář wrote:
> If EPT was enabled, unrestricted_guest was allowed in L1 regardless of
> L0.  L1 triple faulted when running L2 guest that required emulation.
> 
> Another side effect was 'WARN_ON_ONCE(vmx->nested.nested_run_pending)'
> in L0's dmesg:
>   WARNING: CPU: 0 PID: 0 at arch/x86/kvm/vmx.c:9190 nested_vmx_vmexit+0x96e/0xb00 [kvm_intel] ()
> 
> Prevent this scenario by masking SECONDARY_EXEC_UNRESTRICTED_GUEST when
> the host doesn't have it enabled.
> 
> Fixes: 78051e3b7e35 ("KVM: nVMX: Disable unrestricted mode if ept=0")
> Cc: stable@...r.kernel.org
> Tested-By: Kashyap Chamarthy <kchamart@...hat.com>

Thanks Radim, for resending it. I was trying to find it in one of the
recent pull requests. :-)

Just for forerence, test confirmation:

    http://article.gmane.org/gmane.comp.emulators.kvm.devel/133075

Complete thread related to this topic:

    http://thread.gmane.org/gmane.comp.emulators.kvm.devel/132863

-- 
/kashyap

> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  The resend Cc'd stable, as recommended by Bandan, and added Tested-by.
> 
>  arch/x86/kvm/vmx.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 10a481b7674d..ae4f6d35d19c 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2479,8 +2479,7 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
>  	if (enable_ept) {
>  		/* nested EPT: emulate EPT also to L1 */
>  		vmx->nested.nested_vmx_secondary_ctls_high |=
> -			SECONDARY_EXEC_ENABLE_EPT |
> -			SECONDARY_EXEC_UNRESTRICTED_GUEST;
> +			SECONDARY_EXEC_ENABLE_EPT;
>  		vmx->nested.nested_vmx_ept_caps = VMX_EPT_PAGE_WALK_4_BIT |
>  			 VMX_EPTP_WB_BIT | VMX_EPT_2MB_PAGE_BIT |
>  			 VMX_EPT_INVEPT_BIT;
> @@ -2494,6 +2493,10 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
>  	} else
>  		vmx->nested.nested_vmx_ept_caps = 0;
>  
> +	if (enable_unrestricted_guest)
> +		vmx->nested.nested_vmx_secondary_ctls_high |=
> +			SECONDARY_EXEC_UNRESTRICTED_GUEST;
> +
>  	/* miscellaneous data */
>  	rdmsr(MSR_IA32_VMX_MISC,
>  		vmx->nested.nested_vmx_misc_low,
> -- 
> 2.3.2
> 
--
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