Hello all, Thanks for the tip Dan. I thought I would write up what I did for future people searching this list. I added the QEMU command line hook from github oVirt/vdsm (https://github.com/oVirt/vdsm/tree/master/vdsm_hooks/qemucmdline) to /usr/libexec/vdsm/hooks/before_vm_start/ on my hosts. Then I added the Custom Arguments to the config on my machine with the engine running engine-config -g UserDefinedVMProperties # print current args and add them to the next line engine-config -s UserDefinedVMProperties='qemu_cmdline=^.*$' --cver=4.2 Then I was able to add the JSON list of args to the machines in the oVirt UI. Thanks for your help, Harry Harry Mallon CODEX | Senior Software Engineer 60 Poland Street | London | England | W1F 7NT E harry.mallon@codex.online | T +44 203 7000 989