[dpdk-dev] [PATCH 4/4] vhost: destroy unused virtqueues when multiqueue not negotiated

[Maxime Coquelin <maxime.coquelin@redhat.com>]

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>
---
 lib/librte_vhost/vhost_user.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index 7d84af3e2..72526e006 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -173,6 +173,7 @@ vhost_user_get_features(struct virtio_net *dev)
 static int
 vhost_user_set_features(struct virtio_net *dev, uint64_t features)
 {
+	int i;
 	uint64_t vhost_features = 0;
 
 	rte_vhost_driver_get_features(dev->ifname, &vhost_features);
@@ -216,6 +217,24 @@ 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.
+		 */
+		for (i = dev->nr_vring; i > 1; i--) {
+			struct vhost_virtqueue *vq = dev->virtqueue[i];
+
+			if (!vq)
+				continue;
+
+			cleanup_vq(vq, 1);
+			free_vq(vq);
+			dev->nr_vring--;
+		}
+	}
+
 	return 0;
 }
 
-- 
2.14.3