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 --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org
