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
2022-02-01T18:30:30Z

On 2/1/22 15:31, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@redhat.com> 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