Re: [PATCH v5 16/17] KVM: x86: nSVM: always intercept x2apic msrs

[Maxim Levitsky]

On Wed, 2022-05-18 at 20:18 +0300, Maxim Levitsky wrote:
> On Wed, 2022-05-18 at 11:26 -0500, Suravee Suthikulpanit wrote:
> > From: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> > 
> > As a preparation for x2avic, this patch ensures that x2apic msrs
> > are always intercepted for the nested guest.
> > 
> > Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> > Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> > Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> > ---
> >  arch/x86/kvm/svm/nested.c | 5 +++++
> >  arch/x86/kvm/svm/svm.h    | 9 +++++++++
> >  2 files changed, 14 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> > index f209c1ca540c..b61f8939c210 100644
> > --- a/arch/x86/kvm/svm/nested.c
> > +++ b/arch/x86/kvm/svm/nested.c
> > @@ -230,6 +230,11 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
> >  			break;
> >  
> >  		p      = msrpm_offsets[i];
> > +
> > +		/* x2apic msrs are intercepted always for the nested guest */
> > +		if (is_x2apic_msrpm_offset(p))
> > +			continue;
> > +
> >  		offset = svm->nested.ctl.msrpm_base_pa + (p * 4);
> >  
> >  		if (kvm_vcpu_read_guest(&svm->vcpu, offset, &value, 4))
> > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> > index 818817b11f53..309445619756 100644
> > --- a/arch/x86/kvm/svm/svm.h
> > +++ b/arch/x86/kvm/svm/svm.h
> > @@ -517,6 +517,15 @@ static inline bool nested_npt_enabled(struct vcpu_svm *svm)
> >  	return svm->nested.ctl.nested_ctl & SVM_NESTED_CTL_NP_ENABLE;
> >  }
> >  
> > +static inline bool is_x2apic_msrpm_offset(u32 offset)
> > +{
> > +	/* 4 msrs per u8, and 4 u8 in u32 */
> > +	u32 msr = offset * 16;
> > +
> > +	return (msr >= APIC_BASE_MSR) &&
> > +	       (msr < (APIC_BASE_MSR + 0x100));
> > +}
> > +
> >  /* svm.c */
> >  #define MSR_INVALID				0xffffffffU
> >  
> 
> Just one thing, this patch should be earlier in the series (or even first one),
> to avoid having a commit window where the problem exists, where malicious
> L1 can get access to L0's apic msrs this way.
> 
> Best regards,
> 	Maxim Levitsky

Besides this, I guess I currently don't see anything else seriously wrong with this patch
series.

Hopefully I didn't miss anything serious.

Best regards,
	Maxim Levitsky