Re: [PATCH 0/5] KVM: SVM: nSVM: Implement Enlightened MSR-Bitmap for Hyper-V-on-KVM and fix it for KVM-on-Hyper-V

[Paolo Bonzini]

On 2/1/22 15:31, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:
>
> > On 12/20/21 16:21, Vitaly Kuznetsov wrote:
> > > Enlightened MSR-Bitmap feature implements a PV protocol for L0 and L1
> > > hypervisors to collaborate and skip unneeded updates to MSR-Bitmap.
> > > KVM implements the feature for KVM-on-Hyper-V but it seems there was
> > > a flaw in the implementation and the feature may not be fully functional.
> > > PATCHes 1-2 fix the problem. The rest of the series implements the same
> > > feature for Hyper-V-on-KVM.
> > >
> > > Vitaly Kuznetsov (5):
> > >     KVM: SVM: Drop stale comment from
> > >       svm_hv_vmcb_dirty_nested_enlightenments()
> > >     KVM: SVM: hyper-v: Enable Enlightened MSR-Bitmap support for real
> > >     KVM: nSVM: Track whether changes in L0 require MSR bitmap for L2 to be
> > >       rebuilt
> > >     KVM: x86: Make kvm_hv_hypercall_enabled() static inline
> > >     KVM: nSVM: Implement Enlightened MSR-Bitmap feature
> > >
> > >    arch/x86/kvm/hyperv.c           | 12 +--------
> > >    arch/x86/kvm/hyperv.h           |  6 ++++-
> > >    arch/x86/kvm/svm/nested.c       | 47 ++++++++++++++++++++++++++++-----
> > >    arch/x86/kvm/svm/svm.c          |  3 ++-
> > >    arch/x86/kvm/svm/svm.h          | 16 +++++++----
> > >    arch/x86/kvm/svm/svm_onhyperv.h | 12 +++------
> > >    6 files changed, 63 insertions(+), 33 deletions(-)
> >
> > Queued 3-5 now, but it would be nice to have some testcases.

Hmm, it fails to compile with CONFIG_HYPERV disabled, and a trivial
#if also fails due to an unused goto label.  Does this look good to you?

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index e3759a79d39a..a2b5267b3e73 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -173,9 +173,16 @@ void recalc_intercepts(struct vcpu_svm *svm)
  */
 static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
 {
+	int i;
+
+	if (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT)))
+		return true;
+
+	svm->vmcb->control.msrpm_base_pa = __sme_set(__pa(svm->nested.msrpm));
+
+#if IS_ENABLED(CONFIG_HYPERV)
 	struct hv_enlightenments *hve =
 		(struct hv_enlightenments *)svm->nested.ctl.reserved_sw;
-	int i;
 
 	/*
 	 * MSR bitmap update can be skipped when:
@@ -185,10 +192,8 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
 	    kvm_hv_hypercall_enabled(&svm->vcpu) &&
 	    hve->hv_enlightenments_control.msr_bitmap &&
 	    (svm->nested.ctl.clean & VMCB_HV_NESTED_ENLIGHTENMENTS))
-		goto set_msrpm_base_pa;
-
-	if (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT)))
 		return true;
+#endif
 
 	for (i = 0; i < MSRPM_OFFSETS; i++) {
 		u32 value, p;
@@ -213,10 +216,6 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
 	}
 
 	svm->nested.force_msr_bitmap_recalc = false;
-
-set_msrpm_base_pa:
-	svm->vmcb->control.msrpm_base_pa = __sme_set(__pa(svm->nested.msrpm));
-
 	return true;
 }
 


Thanks,

Paolo