I did some test. Linux PVM live migration works well on Xen3.4. As you said above, PVHVM fails live migration and got error: "Error: /usr/lib/xen/bin/xc_save 32 8 0 0 5 failed", but save/restore is OK.It's a problem that affects any PVonHVM domain afaict, so I'd rather defer to the person who made the change originally.