Re: [Qemu-devel] [PATCH] net/virtio: fix multi-queue negotiation

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jun 23, 2015 at 01:23:10PM +0300, Marcel Apfelbaum wrote:
> On 06/23/2015 12:57 PM, Michael S. Tsirkin wrote:
> >On Thu, Jun 18, 2015 at 09:05:44PM +0300, Marcel Apfelbaum wrote:
> >>Clear host multi-queue related features if the peer
> >>doesn't support it.
> >>
> >>Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
> >>---
> >>Notes:
> >>  This fixes a guest CPU soft lock, however the virtio-net
> >>  device will not work correctly. It seems that is
> >>  peer's "fault", not knowing how to handle the situation.
> >>  However, I submit this patch since it corrects the negotiation
> >>  and saves us from a guest crash (!).
> >>
> >>  Any ideas from the virtio/multi-queue developers on how to debug
> >>  this further are welcomed.
> >>
> >>  hw/net/virtio-net.c | 13 ++++++++++++-
> >>  1 file changed, 12 insertions(+), 1 deletion(-)
> >>
> >>diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> >>index 9281aa1..63e59e8 100644
> >>--- a/hw/net/virtio-net.c
> >>+++ b/hw/net/virtio-net.c
> >>@@ -367,6 +367,11 @@ static int peer_has_ufo(VirtIONet *n)
> >>      return n->has_ufo;
> >>  }
> >>
> >>+static int peer_has_multiqueue(VirtIONet *n)
> >>+{
> >>+    return n->multiqueue;
> >>+}
> >>+
> >>  static void virtio_net_set_mrg_rx_bufs(VirtIONet *n, int mergeable_rx_bufs,
> >>                                         int version_1)
> >>  {
> >>@@ -469,6 +474,13 @@ static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features)
> >>          virtio_clear_feature(&features, VIRTIO_NET_F_HOST_UFO);
> >>      }
> >>
> >>+    if (!peer_has_multiqueue(n)) {
> >>+        virtio_clear_feature(&features, VIRTIO_NET_F_MQ);
> >>+        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_ANNOUNCE);
> >>+        virtio_clear_feature(&features, VIRTIO_NET_F_CTRL_VQ);
> >>+        virtio_clear_feature(&features, VIRTIO_NET_F_CTRL_RX);
> >>+    }
> >>+
> >>      if (!get_vhost_net(nc->peer)) {
> >>          virtio_add_feature(&features, VIRTIO_F_VERSION_1);
> >>          return features;
> >
> >_MQ makes sense but what about the rest? Why clear them?
> Guest's virtio driver doesn't like if MQ is off and any of the other flags remains ON.
> It has a specific check for each of them and fails the loading if not all are off.
> 
> Thanks,
> Marcel


I think you are mistaken.

        if (!virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ) &&
            (VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_RX,
                             "VIRTIO_NET_F_CTRL_VQ") ||
             VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_VLAN,
                             "VIRTIO_NET_F_CTRL_VQ") ||
             VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_GUEST_ANNOUNCE,
                             "VIRTIO_NET_F_CTRL_VQ") ||
             VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_MQ, "VIRTIO_NET_F_CTRL_VQ") ||
             VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_MAC_ADDR,
                             "VIRTIO_NET_F_CTRL_VQ"))) {
                return false;
        }

        return true;

So if CTRL VQ is not set, you can not have MQ or any of the others.



> >
> >>@@ -1314,7 +1326,6 @@ static void virtio_net_tx_bh(void *opaque)
> >>  static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue)
> >>  {
> >>      n->multiqueue = multiqueue;
> >>-
> >>      virtio_net_set_queues(n);
> >>  }
> >>
> >>--
> >>2.1.0