KVM: nVMX: Allow restore nested-state to enable eVMCS when vCPU in SMM

As comment in code specifies, SMM temporarily disables VMX so we cannot
be in guest mode, nor can VMLAUNCH/VMRESUME be pending.

However, code currently assumes that these are the only flags that can be
set on kvm_state->flags. This is not true as KVM_STATE_NESTED_EVMCS
can also be set on this field to signal that eVMCS should be enabled.

Therefore, fix code to check for guest-mode and pending VMLAUNCH/VMRESUME
explicitly.
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -5373,7 +5373,10 @@ static int vmx_set_nested_state(struct kvm_vcpu *vcpu,
 	 * nor can VMLAUNCH/VMRESUME be pending.  Outside SMM, SMM flags
 	 * must be zero.
 	 */
-	if (is_smm(vcpu) ? kvm_state->flags : kvm_state->hdr.vmx.smm.flags)
+	if (is_smm(vcpu) ?
+		(kvm_state->flags &
+		 (KVM_STATE_NESTED_GUEST_MODE | KVM_STATE_NESTED_RUN_PENDING))
+		: kvm_state->hdr.vmx.smm.flags)
 		return -EINVAL;
 
 	if ((kvm_state->hdr.vmx.smm.flags & KVM_STATE_NESTED_SMM_GUEST_MODE) &&