On Thu, Apr 19, 2018 at 06:07:07PM +0200, Paolo Bonzini wrote: > On 19/04/2018 17:59, Michael S. Tsirkin wrote: > > 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. > > > > Oh you are right. Well we can just special-case that one :) > > Anything wrong with bumping the PCI revision? > > Paolo
Nothing except in virtio 1 bumping the revision does not prevent loading the old driver. -- MST --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org
