[dpdk-dev] [RFC 08/14] vhost: improve IO vector logic

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

IO vectors and their iterators arrays were part of the
async metadata but not their indexes.

In order to makes this more consistent, the patch adds the
indexes to the async metadata. Doing that, we can avoid
triggering DMA transfer within the loop as it IO vector
index overflow is now prevented in the async_mbuf_to_desc()
function.

Note that previous detection mechanism was broken
since the overflow already happened when detected, so OOB
memory access would already have happened.

With this changes done, virtio_dev_rx_async_submit_split()
and virtio_dev_rx_async_submit_packed() can be further
simplified.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 lib/vhost/vhost.h      |   2 +
 lib/vhost/virtio_net.c | 296 +++++++++++++++++++----------------------
 2 files changed, 136 insertions(+), 162 deletions(-)

diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index dae9a1ac2d..812d4c55a5 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -134,6 +134,8 @@ struct vhost_async {
 
 	struct rte_vhost_iov_iter iov_iter[VHOST_MAX_ASYNC_IT];
 	struct rte_vhost_iovec iovec[VHOST_MAX_ASYNC_VEC];
+	uint16_t iter_idx;
+	uint16_t iovec_idx;
 
 	/* data transfer status */
 	struct async_inflight_info *pkts_info;
diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
index ae7dded979..5ce4c14a73 100644
--- a/lib/vhost/virtio_net.c
+++ b/lib/vhost/virtio_net.c
@@ -924,33 +924,91 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	return error;
 }
 
+static __rte_always_inline int
+async_iter_initialize(struct vhost_async *async)
+{
+	struct rte_vhost_iov_iter *iter;
+
+	if (unlikely(async->iter_idx >= VHOST_MAX_ASYNC_IT)) {
+		VHOST_LOG_DATA(ERR, "no more async iterators available\n");
+		return -1;
+	}
+
+	if (unlikely(async->iovec_idx >= VHOST_MAX_ASYNC_VEC)) {
+		VHOST_LOG_DATA(ERR, "no more async iovec available\n");
+		return -1;
+	}
+
+
+	iter = async->iov_iter + async->iter_idx;
+	iter->iov = async->iovec + async->iovec_idx;
+	iter->nr_segs = 0;
+
+	return 0;
+}
+
+static __rte_always_inline int
+async_iter_add_iovec(struct vhost_async *async, void *src, void *dst, size_t len)
+{
+	struct rte_vhost_iov_iter *iter;
+	struct rte_vhost_iovec *iovec;
+
+	if (unlikely(async->iovec_idx >= VHOST_MAX_ASYNC_VEC)) {
+		VHOST_LOG_DATA(ERR, "no more async iovec available\n");
+		return -1;
+	}
+
+	iter = async->iov_iter + async->iter_idx;
+	iovec = async->iovec + async->iovec_idx;
+
+	iovec->src_addr = src;
+	iovec->dst_addr = dst;
+	iovec->len = len;
+
+	iter->nr_segs++;
+
+	return 0;
+}
+
 static __rte_always_inline void
-async_fill_vec(struct rte_vhost_iovec *v, void *src, void *dst, size_t len)
+async_iter_finalize(struct vhost_async *async)
 {
-	v->src_addr = src;
-	v->dst_addr = dst;
-	v->len = len;
+	async->iter_idx++;
 }
 
 static __rte_always_inline void
-async_fill_iter(struct rte_vhost_iov_iter *it, struct rte_vhost_iovec *vec, unsigned long nr_seg)
+async_iter_cancel(struct vhost_async *async)
 {
-	it->iov = vec;
-	it->nr_segs = nr_seg;
+	struct rte_vhost_iov_iter *iter;
+
+	iter = async->iov_iter + async->iter_idx;
+	async->iovec_idx -= iter->nr_segs;
+	iter->nr_segs = 0;
+	iter->iov = NULL;
 }
 
 static __rte_always_inline void
-async_fill_desc(struct rte_vhost_async_desc *desc, struct rte_vhost_iov_iter *iter)
+async_iter_reset(struct vhost_async *async)
 {
-	desc->iter = iter;
+	async->iter_idx = 0;
+	async->iovec_idx = 0;
+}
+
+static __rte_always_inline void
+async_fill_descs(struct vhost_async *async, struct rte_vhost_async_desc *descs)
+{
+	int i;
+
+	for (i = 0; i < async->iter_idx; i++)
+		descs[i].iter = async->iov_iter + i;
 }
 
 static __rte_always_inline int
 async_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
 			struct rte_mbuf *m, struct buf_vector *buf_vec,
-			uint16_t nr_vec, uint16_t num_buffers,
-			struct rte_vhost_iovec *iovec, struct rte_vhost_iov_iter *iter)
+			uint16_t nr_vec, uint16_t num_buffers)
 {
+	struct vhost_async *async = vq->async;
 	struct rte_mbuf *hdr_mbuf;
 	struct virtio_net_hdr_mrg_rxbuf tmp_hdr, *hdr = NULL;
 	uint64_t buf_addr, buf_iova;
@@ -960,24 +1018,18 @@ async_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	uint32_t mbuf_offset, mbuf_avail;
 	uint32_t buf_offset, buf_avail;
 	uint32_t cpy_len, buf_len;
-	int error = 0;
 
-	int tvec_idx = 0;
 	void *hpa;
 
-	if (unlikely(m == NULL)) {
-		error = -1;
-		goto out;
-	}
+	if (unlikely(m == NULL))
+		return -1;
 
 	buf_addr = buf_vec[vec_idx].buf_addr;
 	buf_iova = buf_vec[vec_idx].buf_iova;
 	buf_len = buf_vec[vec_idx].buf_len;
 
-	if (unlikely(buf_len < dev->vhost_hlen && nr_vec <= 1)) {
-		error = -1;
-		goto out;
-	}
+	if (unlikely(buf_len < dev->vhost_hlen && nr_vec <= 1))
+		return -1;
 
 	hdr_mbuf = m;
 	hdr_addr = buf_addr;
@@ -1005,14 +1057,15 @@ async_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	mbuf_avail  = rte_pktmbuf_data_len(m);
 	mbuf_offset = 0;
 
+	if (async_iter_initialize(async))
+		return -1;
+
 	while (mbuf_avail != 0 || m->next != NULL) {
 		/* done with current buf, get the next one */
 		if (buf_avail == 0) {
 			vec_idx++;
-			if (unlikely(vec_idx >= nr_vec)) {
-				error = -1;
-				goto out;
-			}
+			if (unlikely(vec_idx >= nr_vec))
+				goto error;
 
 			buf_addr = buf_vec[vec_idx].buf_addr;
 			buf_iova = buf_vec[vec_idx].buf_iova;
@@ -1058,26 +1111,30 @@ async_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
 			if (unlikely(!hpa)) {
 				VHOST_LOG_DATA(ERR, "(%d) %s: failed to get hpa.\n",
 				dev->vid, __func__);
-				error = -1;
-				goto out;
+				goto error;
 			}
 
-			async_fill_vec(iovec + tvec_idx,
-				(void *)(uintptr_t)rte_pktmbuf_iova_offset(m,
-				mbuf_offset), hpa, (size_t)mapped_len);
+			if (unlikely(async_iter_add_iovec(async,
+					(void *)(uintptr_t)rte_pktmbuf_iova_offset(m,
+						mbuf_offset),
+					hpa, (size_t)mapped_len)))
+				goto error;
 
 			cpy_len -= (uint32_t)mapped_len;
 			mbuf_avail  -= (uint32_t)mapped_len;
 			mbuf_offset += (uint32_t)mapped_len;
 			buf_avail  -= (uint32_t)mapped_len;
 			buf_offset += (uint32_t)mapped_len;
-			tvec_idx++;
 		}
 	}
 
-	async_fill_iter(iter, iovec, tvec_idx);
-out:
-	return error;
+	async_iter_finalize(async);
+
+	return 0;
+error:
+	async_iter_cancel(async);
+
+	return -1;
 }
 
 static __rte_always_inline int
@@ -1487,18 +1544,16 @@ virtio_dev_rx_async_submit_split(struct virtio_net *dev,
 	struct rte_mbuf **pkts, uint32_t count)
 {
 	struct buf_vector buf_vec[BUF_VECTOR_MAX];
-	uint32_t pkt_idx = 0, pkt_burst_idx = 0;
+	uint32_t pkt_idx = 0;
 	uint16_t num_buffers;
 	uint16_t avail_head;
 
 	struct vhost_async *async = vq->async;
-	struct rte_vhost_iov_iter *iter = async->iov_iter;
-	struct rte_vhost_async_desc tdes[MAX_PKT_BURST];
-	struct rte_vhost_iovec *iovec = async->iovec;
+	struct rte_vhost_async_desc async_descs[MAX_PKT_BURST];
 	struct async_inflight_info *pkts_info = async->pkts_info;
-	uint32_t n_pkts = 0, pkt_err = 0;
+	uint32_t pkt_err = 0;
 	int32_t n_xfer;
-	uint16_t iovec_idx = 0, it_idx = 0, slot_idx = 0;
+	uint16_t slot_idx = 0;
 
 	/*
 	 * The ordering between avail index and desc reads need to be enforced.
@@ -1507,95 +1562,53 @@ virtio_dev_rx_async_submit_split(struct virtio_net *dev,
 
 	rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
 
+	async_iter_reset(async);
+
 	for (pkt_idx = 0; pkt_idx < count; pkt_idx++) {
 		uint32_t pkt_len = pkts[pkt_idx]->pkt_len + dev->vhost_hlen;
 		uint16_t nr_vec = 0;
 
-		if (unlikely(reserve_avail_buf_split(dev, vq,
-						pkt_len, buf_vec, &num_buffers,
-						avail_head, &nr_vec) < 0)) {
-			VHOST_LOG_DATA(DEBUG,
-				"(%d) failed to get enough desc from vring\n",
-				dev->vid);
+		if (unlikely(reserve_avail_buf_split(dev, vq, pkt_len, buf_vec,
+						&num_buffers, avail_head, &nr_vec) < 0)) {
+			VHOST_LOG_DATA(DEBUG, "(%d) failed to get enough desc from vring\n",
+					dev->vid);
 			vq->shadow_used_idx -= num_buffers;
 			break;
 		}
 
 		VHOST_LOG_DATA(DEBUG, "(%d) current index %d | end index %d\n",
-			dev->vid, vq->last_avail_idx,
-			vq->last_avail_idx + num_buffers);
+			dev->vid, vq->last_avail_idx, vq->last_avail_idx + num_buffers);
 
-		if (async_mbuf_to_desc(dev, vq, pkts[pkt_idx], buf_vec, nr_vec, num_buffers,
-				&iovec[iovec_idx], &iter[it_idx]) < 0) {
+		if (async_mbuf_to_desc(dev, vq, pkts[pkt_idx], buf_vec, nr_vec, num_buffers) < 0) {
 			vq->shadow_used_idx -= num_buffers;
 			break;
 		}
 
-		async_fill_desc(&tdes[pkt_burst_idx++], &iter[it_idx]);
-
 		slot_idx = (async->pkts_idx + pkt_idx) & (vq->size - 1);
 		pkts_info[slot_idx].descs = num_buffers;
 		pkts_info[slot_idx].mbuf = pkts[pkt_idx];
 
-		iovec_idx += iter[it_idx].nr_segs;
-		it_idx++;
-
 		vq->last_avail_idx += num_buffers;
+	}
 
-		/*
-		 * condition to trigger async device transfer:
-		 * - unused async iov number is less than max vhost vector
-		 */
-		if (unlikely(VHOST_MAX_ASYNC_VEC - iovec_idx < BUF_VECTOR_MAX)) {
-			n_xfer = async->ops.transfer_data(dev->vid,
-					queue_id, tdes, 0, pkt_burst_idx);
-			if (likely(n_xfer >= 0)) {
-				n_pkts = n_xfer;
-			} else {
-				VHOST_LOG_DATA(ERR,
-					"(%d) %s: failed to transfer data for queue id %d.\n",
-					dev->vid, __func__, queue_id);
-				n_pkts = 0;
-			}
-
-			iovec_idx = 0;
-			it_idx = 0;
-
-			if (unlikely(n_pkts < pkt_burst_idx)) {
-				/*
-				 * log error packets number here and do actual
-				 * error processing when applications poll
-				 * completion
-				 */
-				pkt_err = pkt_burst_idx - n_pkts;
-				pkt_idx++;
-				pkt_burst_idx = 0;
-				break;
-			}
+	if (unlikely(pkt_idx == 0))
+		return 0;
 
-			pkt_burst_idx = 0;
-		}
-	}
+	async_fill_descs(async, async_descs);
 
-	if (pkt_burst_idx) {
-		n_xfer = async->ops.transfer_data(dev->vid, queue_id, tdes, 0, pkt_burst_idx);
-		if (likely(n_xfer >= 0)) {
-			n_pkts = n_xfer;
-		} else {
-			VHOST_LOG_DATA(ERR, "(%d) %s: failed to transfer data for queue id %d.\n",
+	n_xfer = async->ops.transfer_data(dev->vid, queue_id, async_descs, 0, pkt_idx);
+	if (unlikely(n_xfer < 0)) {
+		VHOST_LOG_DATA(ERR, "(%d) %s: failed to transfer data for queue id %d.\n",
 				dev->vid, __func__, queue_id);
-			n_pkts = 0;
-		}
-
-		if (unlikely(n_pkts < pkt_burst_idx))
-			pkt_err = pkt_burst_idx - n_pkts;
+		n_xfer = 0;
 	}
 
+	pkt_err = pkt_idx - n_xfer;
 	if (unlikely(pkt_err)) {
 		uint16_t num_descs = 0;
 
 		/* update number of completed packets */
-		pkt_idx -= pkt_err;
+		pkt_idx = n_xfer;
 
 		/* calculate the sum of descriptors to revert */
 		while (pkt_err-- > 0) {
@@ -1686,9 +1699,7 @@ vhost_enqueue_async_packed(struct virtio_net *dev,
 			    struct rte_mbuf *pkt,
 			    struct buf_vector *buf_vec,
 			    uint16_t *nr_descs,
-			    uint16_t *nr_buffers,
-			    struct rte_vhost_iovec *iovec,
-			    struct rte_vhost_iov_iter *iter)
+			    uint16_t *nr_buffers)
 {
 	uint16_t nr_vec = 0;
 	uint16_t avail_idx = vq->last_avail_idx;
@@ -1736,7 +1747,7 @@ vhost_enqueue_async_packed(struct virtio_net *dev,
 	}
 
 	if (unlikely(async_mbuf_to_desc(dev, vq, pkt, buf_vec, nr_vec,
-					*nr_buffers, iovec, iter) < 0))
+					*nr_buffers) < 0))
 		return -1;
 
 	vhost_shadow_enqueue_packed(vq, buffer_len, buffer_buf_id, buffer_desc_count, *nr_buffers);
@@ -1746,13 +1757,12 @@ vhost_enqueue_async_packed(struct virtio_net *dev,
 
 static __rte_always_inline int16_t
 virtio_dev_rx_async_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
-			    struct rte_mbuf *pkt, uint16_t *nr_descs, uint16_t *nr_buffers,
-			    struct rte_vhost_iovec *iovec, struct rte_vhost_iov_iter *iter)
+			    struct rte_mbuf *pkt, uint16_t *nr_descs, uint16_t *nr_buffers)
 {
 	struct buf_vector buf_vec[BUF_VECTOR_MAX];
 
-	if (unlikely(vhost_enqueue_async_packed(dev, vq, pkt, buf_vec, nr_descs, nr_buffers,
-						 iovec, iter) < 0)) {
+	if (unlikely(vhost_enqueue_async_packed(dev, vq, pkt, buf_vec,
+					nr_descs, nr_buffers) < 0)) {
 		VHOST_LOG_DATA(DEBUG, "(%d) failed to get enough desc from vring\n", dev->vid);
 		return -1;
 	}
@@ -1794,20 +1804,17 @@ virtio_dev_rx_async_submit_packed(struct virtio_net *dev,
 	struct vhost_virtqueue *vq, uint16_t queue_id,
 	struct rte_mbuf **pkts, uint32_t count)
 {
-	uint32_t pkt_idx = 0, pkt_burst_idx = 0;
+	uint32_t pkt_idx = 0;
 	uint32_t remained = count;
 	int32_t n_xfer;
 	uint16_t num_buffers;
 	uint16_t num_descs;
 
 	struct vhost_async *async = vq->async;
-	struct rte_vhost_iov_iter *iter = async->iov_iter;
-	struct rte_vhost_async_desc tdes[MAX_PKT_BURST];
-	struct rte_vhost_iovec *iovec = async->iovec;
+	struct rte_vhost_async_desc async_descs[MAX_PKT_BURST];
 	struct async_inflight_info *pkts_info = async->pkts_info;
-	uint32_t n_pkts = 0, pkt_err = 0;
+	uint32_t pkt_err = 0;
 	uint16_t slot_idx = 0;
-	uint16_t iovec_idx = 0, it_idx = 0;
 
 	do {
 		rte_prefetch0(&vq->desc_packed[vq->last_avail_idx]);
@@ -1815,71 +1822,36 @@ virtio_dev_rx_async_submit_packed(struct virtio_net *dev,
 		num_buffers = 0;
 		num_descs = 0;
 		if (unlikely(virtio_dev_rx_async_packed(dev, vq, pkts[pkt_idx],
-						&num_descs, &num_buffers,
-						&iovec[iovec_idx], &iter[it_idx]) < 0))
+						&num_descs, &num_buffers) < 0))
 			break;
 
 		slot_idx = (async->pkts_idx + pkt_idx) % vq->size;
 
-		async_fill_desc(&tdes[pkt_burst_idx++], &iter[it_idx]);
 		pkts_info[slot_idx].descs = num_descs;
 		pkts_info[slot_idx].nr_buffers = num_buffers;
 		pkts_info[slot_idx].mbuf = pkts[pkt_idx];
-		iovec_idx += iter[it_idx].nr_segs;
-		it_idx++;
 
 		pkt_idx++;
 		remained--;
 		vq_inc_last_avail_packed(vq, num_descs);
+	} while (pkt_idx < count);
 
-		/*
-		 * condition to trigger async device transfer:
-		 * - unused async iov number is less than max vhost vector
-		 */
-		if (unlikely(VHOST_MAX_ASYNC_VEC - iovec_idx < BUF_VECTOR_MAX)) {
-			n_xfer = async->ops.transfer_data(dev->vid,
-					queue_id, tdes, 0, pkt_burst_idx);
-			if (likely(n_xfer >= 0)) {
-				n_pkts = n_xfer;
-			} else {
-				VHOST_LOG_DATA(ERR,
-					"(%d) %s: failed to transfer data for queue id %d.\n",
-					dev->vid, __func__, queue_id);
-				n_pkts = 0;
-			}
-
-			iovec_idx = 0;
-			it_idx = 0;
-
-			if (unlikely(n_pkts < pkt_burst_idx)) {
-				/*
-				 * log error packets number here and do actual
-				 * error processing when applications poll
-				 * completion
-				 */
-				pkt_err = pkt_burst_idx - n_pkts;
-				pkt_burst_idx = 0;
-				break;
-			}
+	if (unlikely(pkt_idx == 0))
+		return 0;
 
-			pkt_burst_idx = 0;
-		}
-	} while (pkt_idx < count);
+	async_fill_descs(async, async_descs);
 
-	if (pkt_burst_idx) {
-		n_xfer = async->ops.transfer_data(dev->vid, queue_id, tdes, 0, pkt_burst_idx);
-		if (likely(n_xfer >= 0)) {
-			n_pkts = n_xfer;
-		} else {
-			VHOST_LOG_DATA(ERR, "(%d) %s: failed to transfer data for queue id %d.\n",
+	n_xfer = async->ops.transfer_data(dev->vid, queue_id, async_descs, 0, pkt_idx);
+	if (unlikely(n_xfer < 0)) {
+		VHOST_LOG_DATA(ERR, "(%d) %s: failed to transfer data for queue id %d.\n",
 				dev->vid, __func__, queue_id);
-			n_pkts = 0;
-		}
-
-		if (unlikely(n_pkts < pkt_burst_idx))
-			pkt_err = pkt_burst_idx - n_pkts;
+		n_xfer = 0;
 	}
 
+	pkt_err = pkt_idx - n_xfer;
+
+	async_iter_reset(async);
+
 	if (unlikely(pkt_err))
 		dma_error_handler_packed(vq, slot_idx, pkt_err, &pkt_idx);
 
-- 
2.31.1