[dpdk-dev] [PATCH] vhost: disable host TSO for linear buffers without extbuf

[Ilya Maximets]

If linear buffers requested and external buffers are not, vhost
will not be able to receive any buffer that doesn't fit in a
single mbuf.  Moreover, if such a buffer will appear in a vring
it will never be dequeued and the whole vring will become dead
breaking the network connection.

Disable segmentation offloading from the host side to avoid
having such a big buffers.

Cc: Flavio Leitner <fbl at sysclose.org>

Fixes: 5005bcda7123 ("vhost: add support for large buffers")
Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
---

There is still an assumption that users are sane enough to have
MTU sized mbufs in a memory pool and that guest will not change
MTU to higher values.

We, probably, still need to have a check on dequeue path and
drop oversized buffers in case of linear buffers to avoid stuck
of the virtqueue.  Or simply drop support of '+linear -extbuf'
case.

Note: Only compile tested due to lack of HW.

 lib/librte_vhost/socket.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
index 2d3d20804..1036eaad4 100644
--- a/lib/librte_vhost/socket.c
+++ b/lib/librte_vhost/socket.c
@@ -933,6 +933,24 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
 			~(1ULL << VHOST_USER_PROTOCOL_F_PAGEFAULT);
 	}
 
+	/*
+	 * We'll not be able to receive a buffer from guest in linear mode
+	 * without external buffer if it will not fit in a single mbuf, which is
+	 * likely if segmentation offloading enabled.
+	 */
+	if (vsocket->linearbuf && !vsocket->extbuf) {
+		uint64_t seg_offload_features =
+				(1ULL << VIRTIO_NET_F_HOST_TSO4) |
+				(1ULL << VIRTIO_NET_F_HOST_TSO6) |
+				(1ULL << VIRTIO_NET_F_HOST_UFO);
+
+		RTE_LOG(INFO, VHOST_CONFIG,
+			"Linear buffers requested without external buffers, "
+			"disabling host segmentation offloading support\n");
+		vsocket->supported_features &= ~seg_offload_features;
+		vsocket->features &= ~seg_offload_features;
+	}
+
 	if (!(flags & RTE_VHOST_USER_IOMMU_SUPPORT)) {
 		vsocket->supported_features &= ~(1ULL << VIRTIO_F_IOMMU_PLATFORM);
 		vsocket->features &= ~(1ULL << VIRTIO_F_IOMMU_PLATFORM);
-- 
2.17.1