[PATCH 2/4] KVM: nVMX: Make VMPTRST return eVMCS GPA when it is used

VMPTRST with active eVMCS is currently forbidden, however, returning 1
without skipping the instruction will likely result in L1 getting
stuck. While TLFS does not specify the expected behavior, genuine Hyper-V
seems to be returning eVMCS GPA. Implement the same behavior in KVM.

Reported-by: [email protected]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=221841
Signed-off-by: Vitaly Kuznetsov <[email protected]>
---
 arch/x86/kvm/vmx/nested.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 216f54a0b8ae..0f5e4b47ecb1 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5946,7 +5946,7 @@ static int handle_vmptrst(struct kvm_vcpu *vcpu)
 {
 	unsigned long exit_qual = vmx_get_exit_qual(vcpu);
 	u32 instr_info = vmcs_read32(VMX_INSTRUCTION_INFO);
-	gpa_t current_vmptr = to_vmx(vcpu)->nested.current_vmptr;
+	gpa_t current_vmptr;
 	struct x86_exception e;
 	gva_t gva;
 	int r;
@@ -5954,8 +5954,14 @@ static int handle_vmptrst(struct kvm_vcpu *vcpu)
 	if (!nested_vmx_check_permission(vcpu))
 		return 1;
 
-	if (unlikely(nested_vmx_is_evmptr12_valid(to_vmx(vcpu))))
-		return 1;
+	/*
+	 * Hyper-V TLFS does not specify the behavior of VMPTRST when eVMCS is used
+	 * but genuine Hyper-V seems to be returning eVMCS GPA.
+	 */
+	if (nested_vmx_is_evmptr12_valid(to_vmx(vcpu)))
+		current_vmptr = to_vmx(vcpu)->nested.hv_evmcs_vmptr;
+	else
+		current_vmptr = to_vmx(vcpu)->nested.current_vmptr;
 
 	if (get_vmx_mem_address(vcpu, exit_qual, instr_info,
 				true, sizeof(gpa_t), &gva))
-- 
2.55.0