(CCing libvir-list) On Thu, Nov 12, 2015 at 05:35:59PM +0100, Paolo Bonzini wrote: That's an option too. But it will cause breakage when upgrading the host kernel, and force users to live with a broken setup because we don't provide CPU models that work. In addition to providing CPU models that work, I believe it's better to make QEMU CPU models match what is already happening in practice with the existing VMs. The former is not true (the change won't be moot). The latter seems true. AFAIK, the presence of rdtscp in cpu_map.xml only does two things: * Makes libvirt never use "-cpu Opteron_G2,+rdtscp" even if the user explicitly asked for rdtscp (which is a libvirt bug that should be fixed); * Makes libvirt refuse to run Opteron_G2 in hosts that lack rdtscp (which is also a libvirt bug, because it's checking host CPUID directly instead of GET_SUPPORTED_CPUID; libvirt must let QEMU check if the feature is really available). -- Eduardo