Hyper-V TLFS explicitly forbids VMREAD and VMWRITE instructions when
Enlightened VMCS interface is in use:
"Any VMREAD or VMWRITE instructions while an enlightened VMCS is
active is unsupported and can result in unexpected behavior.""
Windows 11 + WSL2 seems to ignore this, attempts to VMREAD VMCS field
0x4404 ("VM-exit interruption information") are observed. Failing
these attempts with nested_vmx_failInvalid() makes such guests
unbootable.
Microsoft confirms this is a Hyper-V bug and claims that it'll get fixed
eventually but for the time being we need a workaround. (Temporary) allow
VMREAD to get data from the currently loaded Enlightened VMCS.
Note: VMWRITE instructions remain forbidden, it is not clear how to
handle them properly and hopefully won't ever be needed.
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
arch/x86/kvm/vmx/evmcs.h | 12 +++++++++
arch/x86/kvm/vmx/nested.c | 55 +++++++++++++++++++++++++++------------
2 files changed, 51 insertions(+), 16 deletions(-)
diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
index 9bc2521b159e..8d70f9aea94b 100644
--- a/arch/x86/kvm/vmx/evmcs.h
+++ b/arch/x86/kvm/vmx/evmcs.h
@@ -98,6 +98,18 @@ static __always_inline int evmcs_field_offset(unsigned long field,
return evmcs_field->offset;
}
+static inline u64 evmcs_read_any(struct hv_enlightened_vmcs *evmcs,
+ unsigned long field, u16 offset)
+{
+ /*
+ * vmcs12_read_any() doesn't care whether the supplied structure
+ * is 'struct vmcs12' or 'struct hv_enlightened_vmcs' as it takes
+ * the exact offset of the required field, use it for convenience
+ * here.
+ */
+ return vmcs12_read_any((void *)evmcs, field, offset);
+}
+
#if IS_ENABLED(CONFIG_HYPERV)
static __always_inline int get_evmcs_offset(unsigned long field,
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 5941ba05b509..9758448479b4 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -7,6 +7,7 @@
#include <asm/mmu_context.h>
#include "cpuid.h"
+#include "evmcs.h"
#include "hyperv.h"
#include "mmu.h"
#include "nested.h"
@@ -5099,27 +5100,49 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
if (!nested_vmx_check_permission(vcpu))
return 1;
- /*
- * In VMX non-root operation, when the VMCS-link pointer is INVALID_GPA,
- * any VMREAD sets the ALU flags for VMfailInvalid.
- */
- if (vmx->nested.current_vmptr == INVALID_GPA ||
- (is_guest_mode(vcpu) &&
- get_vmcs12(vcpu)->vmcs_link_pointer == INVALID_GPA))
- return nested_vmx_failInvalid(vcpu);
-
/* Decode instruction info and find the field to read */
field = kvm_register_read(vcpu, (((instr_info) >> 28) & 0xf));
- offset = get_vmcs12_field_offset(field);
- if (offset < 0)
- return nested_vmx_fail(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT);
+ if (!evmptr_is_valid(vmx->nested.hv_evmcs_vmptr)) {
+ /*
+ * In VMX non-root operation, when the VMCS-link pointer is INVALID_GPA,
+ * any VMREAD sets the ALU flags for VMfailInvalid.
+ */
+ if (vmx->nested.current_vmptr == INVALID_GPA ||
+ (is_guest_mode(vcpu) &&
+ get_vmcs12(vcpu)->vmcs_link_pointer == INVALID_GPA))
+ return nested_vmx_failInvalid(vcpu);
- if (!is_guest_mode(vcpu) && is_vmcs12_ext_field(field))
- copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12);
+ offset = get_vmcs12_field_offset(field);
+ if (offset < 0)
+ return nested_vmx_fail(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT);
+
+ if (!is_guest_mode(vcpu) && is_vmcs12_ext_field(field))
+ copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12);
+
+ /* Read the field, zero-extended to a u64 value */
+ value = vmcs12_read_any(vmcs12, field, offset);
+ } else {
+ /*
+ * Hyper-V TLFS (as of 6.0b) explicitly states, that while an
+ * enlightened VMCS is active VMREAD/VMWRITE instructions are
+ * unsupported. Unfortunately, certain versions of Windows 11
+ * don't comply with this requirement which is not enforced in
+ * genuine Hyper-V. Allow VMREAD from an enlightened VMCS as a
+ * workaround, as misbehaving guests will panic on VM-Fail.
+ * Note, enlightened VMCS is incompatible with shadow VMCS so
+ * all VMREADs from L2 should go to L1.
+ */
+ if (WARN_ON_ONCE(is_guest_mode(vcpu)))
+ return nested_vmx_failInvalid(vcpu);
- /* Read the field, zero-extended to a u64 value */
- value = vmcs12_read_any(vmcs12, field, offset);
+ offset = evmcs_field_offset(field, NULL);
+ if (offset < 0)
+ return nested_vmx_fail(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT);
+
+ /* Read the field, zero-extended to a u64 value */
+ value = evmcs_read_any(vmx->nested.hv_evmcs, field, offset);
+ }
/*
* Now copy part of this value to register or memory, as requested.
--
2.34.1
