Comment 9 for bug 1869185

On arm64 host-passthrough was already the default in the XML (and the only thing working reliable).

--host-model doesn't work as of today on arm64
uvt-kvm: error: libvirt: unsupported configuration: CPU mode 'host-model' for aarch64 kvm domain on aarch64 host is not supported by hypervisor

While --model host-passthrough as well as --host-passthrough work well.
So on arm64 that has to be the default.

no arg or --model host-passthrough as well as --host-passthrough become:
  <cpu mode='host-passthrough' check='none'/>

The cpu output lists all types as usable='unknown' \o/
People can still manually set something else on arm64 as well now, but it likely won't work.

That implementation now has safe defaults and would allow to not need to change uvtool if qemu/libvirt down the road will support host-model or named types on arm64.