On 2015-02-24 17:30, Radim Krčmář wrote:
> 2015-02-23 19:05+0100, Kashyap Chamarthy:
>> Tested with the _correct_ Kernel[1] (that has Radim's patch) now --
>> applied it on both L0 and L1.
>>
>> Result: Same as before -- Booting L2 causes L1 to reboot. However, the
>> stack trace from `dmesg` on L0 is took slightly different path than
>> before -- it's using MSR handling:
>
> Thanks, the problem was deeper ... L1 enabled unrestricted mode while L0
> had it disabled. L1 could then vmrun a L2 state that L0 would have to
> emulate, but that doesn't work. There are at least these solutions:
>
> 1) don't expose unrestricted_guest when L0 doesn't have it
Reminds me of a patch called "KVM: nVMX: Disable unrestricted mode if
ept=0" by Bandan. I thought that would have caught it - apparently not.
> 2) fix unrestricted mode emulation code
> 3) handle the failure a without killing L1
>
> I'd do just (1) -- emulating unrestricted mode is a loss.
Agreed.
Jan
>
> I have done initial testing and at least qemu-sanity-check works now:
>
> ---8<---
> 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")
> Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> ---
> 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 f7b20b417a3a..dbabea21357b 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2476,8 +2476,7 @@ 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;
> @@ -2491,6 +2490,10 @@ 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,
>
--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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