Another version of the patch, done by changing the on-the-wire protocol as Avi suggested. I've tested this with: old -> old - Migration works, but runs into the bug I'm trying to fix old -> new - Migration works, but runs into the bug I'm trying to fix new -> old - Migration fails gracefully with ioapic version mismatch new -> new - Migration works, and doesn't run into this particular bug Signed-off-by: Chris Lalancette