On Fri, Oct 25, 2019 at 08:16:26AM -0400, Michael S. Tsirkin wrote:
> On Fri, Oct 25, 2019 at 05:54:55PM +0800, Jason Wang wrote:
> > On 2019/10/24 下午6:42, Jason Wang wrote:
> > >
> > > Yes.
> > >
> > >
> > > > And we should try to avoid
> > > > putting ctrl vq and Rx/Tx vqs in the same DMA space to prevent
> > > > guests having the chance to bypass the host (e.g. QEMU) to
> > > > setup the backend accelerator directly.
> > >
> > >
> > > That's really good point. So when "vhost" type is created, parent
> > > should assume addr of ctrl_vq is hva.
> > >
> > > Thanks
> >
> >
> > This works for vhost but not virtio since there's no way for virtio kernel
> > driver to differ ctrl_vq with the rest when doing DMA map. One possible
> > solution is to provide DMA domain isolation between virtqueues. Then ctrl vq
> > can use its dedicated DMA domain for the work.
It might not be a bad idea to let the parent drivers distinguish
between virtio-mdev mdevs and vhost-mdev mdevs in ctrl-vq handling
by mdev's class id.
> >
> > Anyway, this could be done in the future. We can have a version first that
> > doesn't support ctrl_vq.
+1, thanks
> >
> > Thanks
>
> Well no ctrl_vq implies either no offloads, or no XDP (since XDP needs
> to disable offloads dynamically).
>
> if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)
> && (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
> virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
> virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO) ||
> virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))) {
> NL_SET_ERR_MSG_MOD(extack, "Can't set XDP while host is implementing LRO/CSUM, disable LRO/CSUM first");
> return -EOPNOTSUPP;
> }
>
> neither is very attractive.
>
> So yes ok just for development but we do need to figure out how it will
> work down the road in production.
Totally agree.
>
> So really this specific virtio net device does not support control vq,
> instead it supports a different transport specific way to send commands
> to device.
>
> Some kind of extension to the transport? Ideas?
>
>
> --
> MST
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