vhost: destroy unused virtqueues when multiqueue not negotiated

QEMU sends VHOST_USER_SET_VRING_CALL requests for all queues
declared in QEMU command line before the guest is started.
It has the effect in DPDK vhost-user backend to allocate vrings
for all queues declared by QEMU.

If the first driver being used does not support multiqueue,
the device never changes to VIRTIO_DEV_RUNNING state as only
the first queue pair is initialized. One driver impacted by
this bug is virtio-net's iPXE driver which does not support
VIRTIO_NET_F_MQ feature.

It is safe to destroy unused virtqueues in SET_FEATURES request
handler, as it is ensured the device is not in running state
at this stage, so virtqueues aren't being processed.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>

diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index 5ffd8891d9fe50e09bf4bcccade1b9bf61af35ff..e54795a412eab36853f29ff5313ed9ff01ae7cb4 100644 (file)
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -187,6 +187,25 @@ vhost_user_set_features(struct virtio_net *dev, uint64_t features)
                (dev->features & (1 << VIRTIO_NET_F_MRG_RXBUF)) ? "on" : "off",
                (dev->features & (1ULL << VIRTIO_F_VERSION_1)) ? "on" : "off");
 
+       if (!(dev->features & (1ULL << VIRTIO_NET_F_MQ))) {
+               /*
+                * Remove all but first queue pair if MQ hasn't been
+                * negotiated. This is safe because the device is not
+                * running at this stage.
+                */
+               while (dev->nr_vring > 2) {
+                       struct vhost_virtqueue *vq;
+
+                       vq = dev->virtqueue[--dev->nr_vring];
+                       if (!vq)
+                               continue;
+
+                       dev->virtqueue[dev->nr_vring] = NULL;
+                       cleanup_vq(vq, 1);
+                       free_vq(vq);
+               }
+       }
+
        return 0;
 }