I had this issue with a x200 flashed to Libreboot two years ago.
When I ran qemu with --enable-kvm or when I used libvirt (with virt-manager),
it freezed and I was forced to hard shutdown.
The x200 had a a P8400 Core 2 Duo, I don't remember the batch.. but on my
current x200 (with a P8600) and latest Libreboot stable (september 2016), kvm
works great with Linux / BSD / Window$ VM.
I'm not sure if the thing was CPU related.. I don't use Trisquel anymore
these days..
You can disable KVM but virt will be slow as hell though. Try to use jxself's
linux-libre-lts kernel and make sure you're running latest libreboot stable
first as ADFENO suggested.
