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:

quoted

On 2019/10/24 下午6:42, Jason Wang wrote:

quoted

Yes.

quoted

  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.

quoted

Anyway, this could be done in the future. We can have a version first that
doesn't support ctrl_vq.

+1, thanks

quoted

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?


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MST