On Fri, Aug 11, 2017 at 04:09:26PM +0200, Paolo Bonzini wrote: > On 10/08/2017 23:41, Michael S. Tsirkin wrote: > >>> Then we probably should fail probe if vq size is too small. > >> What does this mean? > > > > We must prevent driver from submitting s/g lists > vq size to device. > > What is the rationale for the limit?
So the host knows what it needs to support. > It makes no sense if indirect > descriptors are available, especially because... > > > Either tell linux to avoid s/g lists that are too long, or > > simply fail request if this happens, or refuse to attach driver to device. > > > > Later option would look something like this within probe: > > > > for (i = VIRTIO_SCSI_VQ_BASE; i < num_vqs; i++) > > if (vqs[i]->num < MAX_SG_USED_BY_LINUX) > > goto err; > > > > > > I don't know what's MAX_SG_USED_BY_LINUX though. > > > > ... both virtio-blk and virtio-scsi transmit their own value for the > maximum sg list size (max_seg in virtio-scsi, seg_max in virtio-blk). > > Paolo No other device has it, and it seemed like a good idea to limit it generally at the time. we can fix the spec to relax the requirement for blk and scsi - want to submit a proposal? Alternatively, add a generic field for that. For a quick fix, make sure vq size is >= max sg. -- MST
