On Thu, Apr 19, 2018 at 05:51:51PM +0200, Paolo Bonzini wrote: > On 19/04/2018 17:19, Michael S. Tsirkin wrote: > >> - if we make it 1 when weak barriers are needed, the device also needs > >> to nack feature negotiation (not allow setting the FEATURES_OK) if the > >> bit is not set by the driver. > >> However, that is not enough. Live > >> migration assumes that it is okay to migrate a virtual machine from a > >> source that doesn't support a feature to a destination that supports it. > >> In this case, it would assume that it is okay to migrate from software > >> virtio to hardware virtio. This is wrong because the destination would > >> use weak barriers > > > > You can't migrate between systems with different sets of device features > > right now. > > Yes, you can, exactly because some features are defined not by the > machine type but rather by the host kernel. See virtio_net_get_features > in QEMU's hw/virtio/virtio-net.c, and virtio_set_features_nocheck in > QEMU's hw/virtio/virtio.c. > > Thanks, > > Paolo
Oh you are right. Well we can just special-case that one :) -- MST --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org
