In my setup, I run libvirt on my workstation and run multiple KVMs.
For some tutorials, I needed to be able to run vagrant. Vagrant has a plugin for libvirt, but unfortunately it seems like almost no boxes (I was looking for bento-boxes) support the libvirt provider.
Since these boxes I need to run additionally for this tutorial are rather small and not very busy, I decided to run them without hardware acceleration. This has it's down-sides of course - SLOW, but I don't mind.
To tell vagrant that you do want to run the virtualbox provider without hardware acceleration add a section like this to your Vagrantfile:
config.vm.provider "virtualbox" do |v|
v.customize ["modifyvm", :id, "--hwvirtex", "off"]