Currently, we don't explicitly set the guest CPU model when creating a
virtual machine, and libvirt picks whatever is the platform default. The
libvirt CPU default model is "qemu64/kvm64", which makes Oracle Linux 9
panic on boot, see https://bugzilla.redhat.com/2094260. Setting CPU to
"host" lets libvirt use the closes analog to the host CPU, which works
for Oracle Linux 9.