diff options
| author | Vitaly Kuznetsov <vkuznets@redhat.com> | 2021-11-29 10:47:04 +0100 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2021-12-08 09:06:05 -0500 |
| commit | 502d2bf5f2fd7c05adc2d4f057910bd5d4c4c63e (patch) | |
| tree | d8ee8ec67a899c26faedf70d620d1f07c5162d34 /arch/x86/kvm/hyperv.c | |
| parent | ed2a4800ae9d491e4bf1b8b60b15001ce3b88fcd (diff) | |
| download | linux-502d2bf5f2fd7c05adc2d4f057910bd5d4c4c63e.tar.bz2 | |
KVM: nVMX: Implement Enlightened MSR Bitmap feature
Updating MSR bitmap for L2 is not cheap and rearly needed. TLFS for Hyper-V
offers 'Enlightened MSR Bitmap' feature which allows L1 hypervisor to
inform L0 when it changes MSR bitmap, this eliminates the need to examine
L1's MSR bitmap for L2 every time when 'real' MSR bitmap for L2 gets
constructed.
Use 'vmx->nested.msr_bitmap_changed' flag to implement the feature.
Note, KVM already uses 'Enlightened MSR bitmap' feature when it runs as a
nested hypervisor on top of Hyper-V. The newly introduced feature is going
to be used by Hyper-V guests on KVM.
When the feature is enabled for Win10+WSL2, it shaves off around 700 CPU
cycles from a nested vmexit cost (tight cpuid loop test).
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20211129094704.326635-5-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/hyperv.c')
| -rw-r--r-- | arch/x86/kvm/hyperv.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index 7179fa645eda..a91424ed436d 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -2517,6 +2517,8 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid, case HYPERV_CPUID_NESTED_FEATURES: ent->eax = evmcs_ver; + if (evmcs_ver) + ent->eax |= HV_X64_NESTED_MSR_BITMAP; break; |