Re: [PATCH RESEND] KVM: nVMX: mask unrestricted_guest if disabled on L0

Kashyap Chamarthy
2015-03-17T18:43:15Z

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@vger.kernel.org
> Tested-By: Kashyap Chamarthy <kchamart@redhat.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@redhat.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
>