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

[Marcel Apfelbaum]

Clear host multi-queue related features if the peer
doesn't support it.

Signed-off-by: Marcel Apfelbaum <mar...@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;
@@ -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