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

Vitaly Kuznetsov
2022-02-01T18:59:00Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> 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?
>

Hm, it does but honestly I did not anticipate this dependency --
CONFIG_HYPERV is needed for KVM-on-Hyper-V but this feature is for
Hyper-V-on-KVM. Let me take a look tomorrow.

> 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
>

--
Vitaly