Re: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL unconditionally

Sean Christopherson
2020-05-27T01:21:43Z

On Sat, May 23, 2020 at 07:14:55PM +0300, Maxim Levitsky wrote:
> This msr is only available when the host supports WAITPKG feature.
>
> This breaks a nested guest, if the L1 hypervisor is set to ignore
> unknown msrs, because the only other safety check that the
> kernel does is that it attempts to read the msr and
> rejects it if it gets an exception.
>
> Fixes: 6e3ba4abce KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

Same comments on the line wraps and Fixes tag.

For the code:

Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>

> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
> arch/x86/kvm/x86.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b226fb8abe41b..4752293312947 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5316,6 +5316,10 @@ static void kvm_init_msr_list(void)
> min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
> continue;
> break;
> + case MSR_IA32_UMWAIT_CONTROL:
> + if (!kvm_cpu_cap_has(X86_FEATURE_WAITPKG))
> + continue;
> + break;
> default:
> break;
> }
> --
> 2.26.2
>