[PATCH 5.14 054/172] KVM: nVMX: Filter out all unsupported controls when eVMCS was activated

Greg Kroah-Hartman
2021-10-04T13:32:19Z

From: Vitaly Kuznetsov <vkuznets@redhat.com>

commit 8d68bad6d869fae8f4d50ab6423538dec7da72d1 upstream.

Windows Server 2022 with Hyper-V role enabled failed to boot on KVM when
enlightened VMCS is advertised. Debugging revealed there are two exposed
secondary controls it is not happy with: SECONDARY_EXEC_ENABLE_VMFUNC and
SECONDARY_EXEC_SHADOW_VMCS. These controls are known to be unsupported,
as there are no corresponding fields in eVMCSv1 (see the comment above
EVMCS1_UNSUPPORTED_2NDEXEC definition).

Previously, commit 31de3d2500e4 ("x86/kvm/hyper-v: move VMX controls
sanitization out of nested_enable_evmcs()") introduced the required
filtering mechanism for VMX MSRs but for some reason put only known
to be problematic (and not full EVMCS1_UNSUPPORTED_* lists) controls
there.

Note, Windows Server 2022 seems to have gained some sanity check for VMX
MSRs: it doesn't even try to launch a guest when there's something it
doesn't like, nested_evmcs_check_controls() mechanism can't catch the
problem.

Let's be bold this time and instead of playing whack-a-mole just filter out
all unsupported controls from VMX MSRs.

Fixes: 31de3d2500e4 ("x86/kvm/hyper-v: move VMX controls sanitization out of nested_enable_evmcs()")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210907163530.110066-1-vkuznets@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/vmx/evmcs.c | 12 +++++++++---
arch/x86/kvm/vmx/vmx.c | 9 +++++----
2 files changed, 14 insertions(+), 7 deletions(-)

--- a/arch/x86/kvm/vmx/evmcs.c
+++ b/arch/x86/kvm/vmx/evmcs.c
@@ -354,14 +354,20 @@ void nested_evmcs_filter_control_msr(u32
switch (msr_index) {
case MSR_IA32_VMX_EXIT_CTLS:
case MSR_IA32_VMX_TRUE_EXIT_CTLS:
- ctl_high &= ~VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL;
+ ctl_high &= ~EVMCS1_UNSUPPORTED_VMEXIT_CTRL;
break;
case MSR_IA32_VMX_ENTRY_CTLS:
case MSR_IA32_VMX_TRUE_ENTRY_CTLS:
- ctl_high &= ~VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
+ ctl_high &= ~EVMCS1_UNSUPPORTED_VMENTRY_CTRL;
break;
case MSR_IA32_VMX_PROCBASED_CTLS2:
- ctl_high &= ~SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
+ ctl_high &= ~EVMCS1_UNSUPPORTED_2NDEXEC;
+ break;
+ case MSR_IA32_VMX_PINBASED_CTLS:
+ ctl_high &= ~EVMCS1_UNSUPPORTED_PINCTRL;
+ break;
+ case MSR_IA32_VMX_VMFUNC:
+ ctl_low &= ~EVMCS1_UNSUPPORTED_VMFUNC;
break;
}

--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1840,10 +1840,11 @@ static int vmx_get_msr(struct kvm_vcpu *
&msr_info->data))
return 1;
/*
- * Enlightened VMCS v1 doesn't have certain fields, but buggy
- * Hyper-V versions are still trying to use corresponding
- * features when they are exposed. Filter out the essential
- * minimum.
+ * Enlightened VMCS v1 doesn't have certain VMCS fields but
+ * instead of just ignoring the features, different Hyper-V
+ * versions are either trying to use them and fail or do some
+ * sanity checking and refuse to boot. Filter all unsupported
+ * features out.
*/
if (!msr_info->host_initiated &&
vmx->nested.enlightened_vmcs_enabled)