KVM: nVMX: Reload vmcs01 if getting vmcs12's pages fails

Reload vmcs01 when bailing from nested_vmx_enter_non_root_mode() as KVM
expects vmcs01 to be loaded when is_guest_mode() is false.

Fixes: 671ddc70 ("KVM: nVMX: Don't leak L1 MMIO regions to L2")
Cc: stable@vger.kernel.org
Cc: Dan Cross <dcross@google.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Peter Shier <pshier@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923184452.980-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -3349,8 +3349,10 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 	prepare_vmcs02_early(vmx, vmcs12);
 
 	if (from_vmentry) {
-		if (unlikely(!nested_get_vmcs12_pages(vcpu)))
+		if (unlikely(!nested_get_vmcs12_pages(vcpu))) {
+			vmx_switch_vmcs(vcpu, &vmx->vmcs01);
 			return NVMX_VMENTRY_KVM_INTERNAL_ERROR;
+		}
 
 		if (nested_vmx_check_vmentry_hw(vcpu)) {
 			vmx_switch_vmcs(vcpu, &vmx->vmcs01);