Hi, I'm not sure where the problem lies, hence the CC to both lists. Please copy me on the reply. I'm playing with OpenStack's devstack environment on an Ubuntu 14.04 host with a Celeron 2961Y CPU. (libvirt detects it as a Nehalem with a bunch of extra features.) Qemu gives version 2.2.0 (Debian 1:2.2+dfsg-5expubuntu9.7~cloud2). If I don't specify a virtual CPU model, it appears to give me a "qemu64" CPU, and /proc/cpuinfo in the guest instance looks something like this: processor 0 vendor_id GenuineIntel cpu family 6 model 6 model name: QEMU Virtual CPU version 2.2.0 stepping: 3 microcode: 0x1 flags: fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pse36 clflush mmx fxsr sse sse2 syscall nx lm rep_good nopl pni vmx cx16 x2apic popcnt hypervisor lahf_lm abm vnmi ept However, if I explicitly specify a custom CPU model of "qemu64" the instance refuses to boot and I get a log saying: libvirtError: unsupported configuration: guest and host CPU are not compatible: Host CPU does not provide required features: svmlibvirtError: unsupported configuration: guest and host CPU are not compatible: Host CPU does not provide required features: svm When this happens, some of the XML for the domain looks like this: <os> <type arch='x86_64' machine='pc-i440fx-utopic'>hvm</type> .... <cpu mode='custom' match='exact'> <model fallback='allow'>qemu64</model> <topology sockets='1' cores='1' threads='1'/> </cpu> Of course "svm" is an AMD flag and I'm running an Intel CPU. But why does it work when I just rely on the default virtual CPU? Is kvm_default_unset_features handled differently when it's implicit vs explicit? If I explicitly specify a custom CPU model of "kvm64" then it boots, but of course I get a different virtual CPU from what I get if I don't specify anything. Following some old suggestions I tried turning off nested kvm, deleting /var/cache/libvirt/qemu/capabilities/*, and restarting libvirtd. Didn't help. So...anyone got any ideas what's going on? Is there no way to explicitly specify the model that you get by default? Thanks, Chris