On Mon, 17 Nov 2014 12:28:49 +0200 "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > On Mon, Nov 17, 2014 at 11:20:48AM +0100, Cornelia Huck wrote: > > On Mon, 17 Nov 2014 12:11:39 +0200 > > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > > > On Mon, Nov 17, 2014 at 10:44:30AM +0100, Cornelia Huck wrote: > > > > On Mon, 17 Nov 2014 11:37:01 +0200 > > > > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > > > > > > > On Mon, Nov 17, 2014 at 05:17:17PM +0800, Jason Wang wrote: > > > > > > Buggy host may advertised buggy host features (a usual case is that host > > > > > > advertise a feature whose dependencies were missed). In this case, driver > > > > > > should detect and disable the buggy features by itself. > > > > > > > > > > > > This patch introduces driver specific sanitize_features() method which is > > > > > > called just before features finalizing to detect and disable buggy features > > > > > > advertised by host. > > > > > > > > > > > > Virtio-net will be the first user. > > > > > > > > > > > > Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx> > > > > > > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> > > > > > > Cc: Cornelia Huck <cornelia.huck@xxxxxxxxxx> > > > > > > Cc: Wanlong Gao <gaowanlong@xxxxxxxxxxxxxx> > > > > > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> > > > > > > > > > > Hmm this conflicts with virtio 1.0 work: we drop > > > > > features as bitmap there. > > > > > > > > But that's an implementation detail, no? We'll still need a way for the > > > > driver to sanitize features, and I think this interface works just fine. > > > > > > Now that you mention it, I don't think we do. > > > > > > The spec is quite explicit that devices must not expose invalid > > > combinations of features. > > > > Unfortunately, this does not ensure that there won't be buggy > > hypervisors out there, just as there's buggy hardware floating around. > > > > > > > > Admittedly, BUG_ON isn't very friendly to hypervisors. > > > > > > But e.g. failing probe seems better than trying to work around > > > hypervisor bugs - otherwise we'll be stuck maintaining compatibility > > > with hypervisors forever. > > > > Good point. Failing probe is still much better than hitting BUG_ONs. > > > > We'll still need a driver callback, though, that can return an error on > > bogus feature bit combinations. > > Why bother? Just check features at start of probe, and return an error. So we'd fail probing due to bogus features after setting FEATURES_OK in the virtio-1 case, won't we? Feels a bit weird, but seems to be covered by the spec. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
