Comment 6 for bug 878422

Ok, sorry, Simon, for taking so long. As it turns out, cpu hotplug is simply not yet supported. It had been implemented in qemu-kvm, but near as I can tell it was dropped when it failed to get into qemu.

However, qemu should at least fail more gracefully, or, failing that, libvirt should be refusing to ask qemu to hotplug cpus. If we can't get this fixed upstream soon, then we should carry a patch for LTS.