Re: [PATCH v2 4/4] virtio-net: Add support for USO features

On 2024/08/06 22:29, Michael S. Tsirkin wrote: > On Tue, Aug 06, 2024 at 04:35:44PM +0900, Akihiko Odaki wrote: > > On 2024/08/05 19:08, Michael S. Tsirkin wrote: > > > On Mon, Aug 05, 2024 at 06:37:58PM +0900, Akihiko Odaki wrote: > > > > If cross-migrate=off, QEMU can still migrate on the same host (checkpoint > > > > and restart). QEMU can also migrate across hosts if the user ensures they > > > > are on the same platform. > > > > > > What is so special about checkpoint/restart? I guess we hope that > > > downgrades are uncommon, but they are possible... > > > > Downgrades will not work with cross-migrate=off. Users who want downgrades > > should use cross-migrate=on. > > We also don't know that upgrades do not disable a feature: > can happen if e.g. there's a serious bug in the feature. > Basically, this makes the feature too fragile, in my opinion. We can do nothing in such a case. Whether it is on a single host or multiple hosts, we cannot support migration if features once enabled disappear. Regards, Akihiko Odaki