https://bugzilla.redhat.com/show_bug.cgi?id=1110305 This enabled the hv_relaxed flag on all my Windows VMs, causing them to no longer boot. The same thing would happen if I simply booted from the Windows install media. I would get a screen with a stop error: Your PC needs to restart. Please hold down the power button. Error Code: 0x0000001E Parameters: 0xFFFFFFFFC0000096 0xFFFFF802C4044EA4 0x00000000000000000 0x00000000000000000 I created a file called /etc/ovirt-engine/osinfo.conf.d/01-windows.properties that had one line: os.windows_xp.devices.hyperv.enabled.value = false I restarted ovirt-engine and now I can start my Windows VMs. Why does this occur? Is it because I upgraded from 3.4 to 3.5? Is there something else I'm doing wrong? I would like to not need this workaround. Thanks. Charles