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

[Maxim Levitsky]

On Tue, 2020-05-26 at 18:21 -0700, Sean Christopherson wrote:
> 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.
I rewrote the commit message and I hope that the new version
is better. I fixed the 'fixes' message as well.

> 
> For the code:
> 
> Reviewed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Thank you!

Best regards,
	Maxim Levitsky


> 
> > Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> > ---
> >  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
> >