i have test it and restart services. when i change the cpu_model it seems that i will get an error to instantiate new instance. so what i do is i check the cpu capabilities by using virsh capabilities
command and i can see that my cpu can only run kvm32. when i change to kvm32, i'm able to instantiate new instance, reboot and also live migrations. but it just for 32 bit server.
i believe this is the issue with the processor itself.
one more thing need to take note is to be able to fully run live migration, you will need to have your instance being placed inside a shared storage which has been mount by all of your compute node.
as far as i can see, doing simple migration is enough as what it does is just migrate whole block of image to the new host. libvirt does not check cpu model. what lacking is the instance will be just pause while being transferred to other host, you will see your server will not be available for few minutes.