[libvirt-users] os/type/machine/pc-xxxx meaning ? following live migration issue after an upgrade

Dear All, I have upgrade my hypervisors: qemu-kvm 0.12.5 => 1.1.2 libvirt-bin 0.8.3-5 => 0.9.12.3 (debian6 to debian7) After that upgrade, i noticed that live migration was most of the time failing (freeze) (not always) I also noticed that creating a machine with the updated hypervisor was always working. After some days of investigation mainly on network side, i found this setting that seems to fix the issue in the xml: <os> <type arch='x86_64' machine='pc-0.12'>hvm</type> <boot dev='hd'/> </os> replacing pc-0.12 with pc-1.1 seems to fix the issue. Here are my questions : 1) what is the meaning/purpose of that setting ? (i guess it is somehow linked to the version of kvm ;) ) 2) can i just change it in all xmls ? ( i have plenty of linux/windows flavors running in my vms) 3) is it possible to put a more generic value? So we don't have the same issue on next upgrade. 4) Is there a script/doc that explains what needs to be done on the vm itself (xml or other) when we upgrade libvirt/kvm ? Thanks for the feedback ! Benoit. -- Benoit Rousselle