From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
linux-kernel@vger.kernel.org
Subject: [PATCH 1/4] KVM: nVMX: Don't use Enlightened MSR Bitmap for L3
Date: Fri, 10 Sep 2021 18:06:30 +0200 [thread overview]
Message-ID: <20210910160633.451250-2-vkuznets@redhat.com> (raw)
In-Reply-To: <20210910160633.451250-1-vkuznets@redhat.com>
When KVM runs as a nested hypervisor on top of Hyper-V it uses Enlightened
VMCS and enables Enlightened MSR Bitmap feature for its L1s and L2s (which
are actually L2s and L3s from Hyper-V's perspective). When MSR bitmap is
updated, KVM has to reset HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP from
clean fields to make Hyper-V aware of the change. For KVM's L1s, this is
done in vmx_disable_intercept_for_msr()/vmx_enable_intercept_for_msr().
MSR bitmap for L2 is build in nested_vmx_prepare_msr_bitmap() by blending
MSR bitmap for L1 and L1's idea of MSR bitmap for L2. KVM, however, doesn't
check if the resulting bitmap is different and never cleans
HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP in eVMCS02. This is incorrect and
may result in Hyper-V missing the update.
The issue could've been solved by calling evmcs_touch_msr_bitmap() for
eVMCS02 from nested_vmx_prepare_msr_bitmap() unconditionally but doing so
would not give any performance benefits (compared to not using Enlightened
MSR Bitmap at all). 3-level nesting is also not a very common setup
nowadays.
Don't enable 'Enlightened MSR Bitmap' feature for KVM's L2s (real L3s) for
now.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/kvm/vmx/vmx.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 0c2c0d5ae873..ae470afcb699 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2654,15 +2654,6 @@ int alloc_loaded_vmcs(struct loaded_vmcs *loaded_vmcs)
if (!loaded_vmcs->msr_bitmap)
goto out_vmcs;
memset(loaded_vmcs->msr_bitmap, 0xff, PAGE_SIZE);
-
- if (IS_ENABLED(CONFIG_HYPERV) &&
- static_branch_unlikely(&enable_evmcs) &&
- (ms_hyperv.nested_features & HV_X64_NESTED_MSR_BITMAP)) {
- struct hv_enlightened_vmcs *evmcs =
- (struct hv_enlightened_vmcs *)loaded_vmcs->vmcs;
-
- evmcs->hv_enlightenments_control.msr_bitmap = 1;
- }
}
memset(&loaded_vmcs->host_state, 0, sizeof(struct vmcs_host_state));
@@ -6861,6 +6852,19 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
}
vmx->loaded_vmcs = &vmx->vmcs01;
+
+ /*
+ * Use Hyper-V 'Enlightened MSR Bitmap' feature when KVM runs as a
+ * nested (L1) hypervisor and Hyper-V in L0 supports it.
+ */
+ if (IS_ENABLED(CONFIG_HYPERV) && static_branch_unlikely(&enable_evmcs)
+ && (ms_hyperv.nested_features & HV_X64_NESTED_MSR_BITMAP)) {
+ struct hv_enlightened_vmcs *evmcs =
+ (struct hv_enlightened_vmcs *)vmx->loaded_vmcs->vmcs;
+
+ evmcs->hv_enlightenments_control.msr_bitmap = 1;
+ }
+
cpu = get_cpu();
vmx_vcpu_load(vcpu, cpu);
vcpu->cpu = cpu;
--
2.31.1
next prev parent reply other threads:[~2021-09-10 16:07 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-10 16:06 [PATCH 0/4] KVM: nVMX: Enlightened MSR Bitmap feature for Hyper-V on KVM Vitaly Kuznetsov
2021-09-10 16:06 ` Vitaly Kuznetsov [this message]
2021-09-12 15:58 ` [PATCH 1/4] KVM: nVMX: Don't use Enlightened MSR Bitmap for L3 Maxim Levitsky
2021-09-13 6:53 ` Vitaly Kuznetsov
2021-09-13 11:33 ` Maxim Levitsky
2021-09-10 16:06 ` [PATCH 2/4] KVM: VMX: Introduce vmx_msr_bitmap_l01_changed() helper Vitaly Kuznetsov
2021-09-12 15:58 ` Maxim Levitsky
2021-09-10 16:06 ` [PATCH 3/4] KVM: nVMX: Track whether changes in L0 require MSR bitmap for L2 to be rebuilt Vitaly Kuznetsov
2021-09-12 15:59 ` Maxim Levitsky
2021-09-13 6:57 ` Vitaly Kuznetsov
2021-09-13 11:36 ` Maxim Levitsky
2021-09-10 16:06 ` [PATCH 4/4] KVM: nVMX: Implement Enlightened MSR Bitmap feature Vitaly Kuznetsov
2021-09-12 15:59 ` Maxim Levitsky
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