[dpdk-dev] [PATCH v4 3/4] vhost: fix async vector buffer overrun

[Patrick Fu]

Add check on the async vector buffer usage to prevent the buf overrun.
If the unused vector buffer is not sufficient to prepare for next
packet's iov creation, an async transfer will be triggered immediately
to free the vector buffer.

Fixes: 78639d54563a ("vhost: introduce async enqueue registration API")

Signed-off-by: Patrick Fu <patrick.fu at intel.com>
---
 lib/librte_vhost/vhost.h      |  2 +-
 lib/librte_vhost/virtio_net.c | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 7d1a8d2b7..75d79f80a 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -47,7 +47,7 @@
 #define MAX_PKT_BURST 32
 
 #define VHOST_MAX_ASYNC_IT (MAX_PKT_BURST * 2)
-#define VHOST_MAX_ASYNC_VEC (BUF_VECTOR_MAX * 2)
+#define VHOST_MAX_ASYNC_VEC (BUF_VECTOR_MAX * 4)
 
 #define PACKED_DESC_ENQUEUE_USED_FLAG(w)	\
 	((w) ? (VRING_DESC_F_AVAIL | VRING_DESC_F_USED | VRING_DESC_F_WRITE) : \
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 19ac92c85..74214e81a 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -1493,6 +1493,7 @@ virtio_dev_rx_async_submit_split(struct virtio_net *dev,
 	struct rte_vhost_iov_iter *dst_it = it_pool + 1;
 	uint16_t n_free_slot, slot_idx;
 	uint16_t pkt_err = 0;
+	uint16_t segs_await = 0;
 	struct async_inflight_info *pkts_info = vq->async_pkts_info;
 	int n_pkts = 0;
 
@@ -1541,6 +1542,7 @@ virtio_dev_rx_async_submit_split(struct virtio_net *dev,
 			dst_iovec += dst_it->nr_segs;
 			src_it += 2;
 			dst_it += 2;
+			segs_await += src_it->nr_segs;
 		} else {
 			pkts_info[slot_idx].info = num_buffers;
 			vq->async_pkts_inflight_n++;
@@ -1548,14 +1550,23 @@ virtio_dev_rx_async_submit_split(struct virtio_net *dev,
 
 		vq->last_avail_idx += num_buffers;
 
+		/*
+		 * conditions to trigger async device transfer:
+		 * - buffered packet number reaches transfer threshold
+		 * - this is the last packet in the burst enqueue
+		 * - unused async iov number is less than max vhost vector
+		 */
 		if (pkt_burst_idx >= VHOST_ASYNC_BATCH_THRESHOLD ||
-				(pkt_idx == count - 1 && pkt_burst_idx)) {
+			(pkt_idx == count - 1 && pkt_burst_idx) ||
+			(VHOST_MAX_ASYNC_VEC / 2 - segs_await <
+			BUF_VECTOR_MAX)) {
 			n_pkts = vq->async_ops.transfer_data(dev->vid,
 					queue_id, tdes, 0, pkt_burst_idx);
 			src_iovec = vec_pool;
 			dst_iovec = vec_pool + (VHOST_MAX_ASYNC_VEC >> 1);
 			src_it = it_pool;
 			dst_it = it_pool + 1;
+			segs_await = 0;
 			vq->async_pkts_inflight_n += n_pkts;
 
 			if (unlikely(n_pkts < (int)pkt_burst_idx)) {
-- 
2.18.4