On 20/02/2018 15:59, Van De Ven, Arjan wrote: > >>> I meant software wise. You're not going to live migrate from xen to >>> kvm or backwards. or between very radically different versions of the >>> kvm stack. >> >> Forwards migration to a radically newer version certainly happens. So >> when the source hypervisor was too old to tell the VM about IBRS_ALL, >> for example, migration should work properly and the VM should perform >> well on the destination hypervisor. > > that makes sense, compatibility in this direction can be done > and is useful as you move a fleet of servers forward > >> Backwards migration to older hypervisors also happens sometimes, but in >> general it creates more userspace than kernel issues. > > that direction is obviously harder >From KVM's point of view it's mostly a matter of having a complete ioctl API right. I'm not that much worried by it. Paolo
