Comment 4 for bug 1322681

i had the same problem with icehouse on ubuntu 14.04 LTS and fixed it with the following change in
/usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py

at line 4338 ff i removed

        for f in info['features']:
            cpu.add_feature(vconfig.LibvirtConfigCPUFeature(f))

and replaced it with

        test = []
        for f in info['features']:
            if f not in test:
                test.append(f)
                cpu.add_feature(vconfig.LibvirtConfigCPUFeature(f))

maybe this helps someone until the fix is released.