[SOLVED] How to disable nested virtualization for VM

I want to disable virtualization inside VMs
How can I achieve that?
I think the easiest way is to select a 'CPU Model' which does not have the virtualization instructions - probably 'kvm64' would be a good choice here

I hope this helps!
 
I need to disable the nested virtualization for virtualized pfSense as there is some bug in freeBSD and the VM hangs. If I assign kvm64 CPU the VM boots but I am loosing the AES-NI and other acceleration instructions.
Any idea how to disable the nested virtualization per VM?