The reason I am enabling this in my virtual machine is to develop with android studio under windows or Linux in a dedicated development machine (Let us call it an android development virtual machine), you will need to enable nested virtualization for the virtual android phone that comes with Android studio, there are many occasions where you need nested virtualization, so let us see what we need to do.
1- Check if our system allows nested virtualization with the following line
If this returns a Y or a 1, then we are good to go to the next step, if not, then execute the following to enable the feature on the host system
echo 'options kvm_intel nested=1' >> /etc/modprobe.d/qemu-system-x86.conf
Now, with that out of the way, we can move to the next step
2- Enable nested virtualization in the config of the virtual machine, either with virsh edit or edit the file manually and reload it, whatever you are used to doing should work
virsh edit androiddev
Now, specify either host-model OR host-passthrough, host model is more compatible when moving the virtual machine to a new CPU, while host-passthrough will deliver absolutly all CPU features to the guest os, but is very unfriendly to moving the machine to a different KVM host