Comment 3 for bug 1082414

It is worse than you might imagine. The problem here is that there are two CPU models for each host - the model that the host pCPU has, and the model that the guest vCPU uses. The migration checks are comparing the host CPUs from the two machines. So they can compare as incompatible, even if you've explicitly configured the guest CPU to be a model that is a lowest common denominator. The correct approach is to compare the source guest CPU model with the target host CPU model, but I don't think it is easy todo since, since nothing in the Nova compute APIs exposes any data about guest CPU models. Fixing this correctly is quite a significant job, which I was planning on looking at in Havana. Not sure how practical it is to do a fix for Grizzly.