vhost: fix offload flags in Rx path

The vhost library currently configures Tx offloading (PKT_TX_*) on any
packet received from a guest virtio device which asks for some offloading.

This is problematic, as Tx offloading is something that the application
must ask for: the application needs to configure devices
to support every used offloads (ip, tcp checksumming, tso..), and the
various l2/l3/l4 lengths must be set following any processing that
happened in the application itself.

On the other hand, the received packets are not marked wrt current
packet l3/l4 checksumming info.

Copy virtio rx processing to fix those offload flags with some
differences:
- accept VIRTIO_NET_HDR_GSO_ECN and VIRTIO_NET_HDR_GSO_UDP,
- ignore anything but the VIRTIO_NET_HDR_F_NEEDS_CSUM flag (to comply with
  the virtio spec),

Some applications might rely on the current behavior, so it is left
untouched by default.
A new RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS flag is added to enable the
new behavior.

The vhost example has been updated for the new behavior: TSO is applied to
any packet marked LRO.

Fixes: 859b480d5afd ("vhost: add guest offload setting")
Cc: stable@dpdk.org

Signed-off-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

doc/guides/prog_guide/vhost_lib.rst

@@ -118,6 +118,18 @@ The following is an overview of some key Vhost API functions:
 
     It is disabled by default.
 
+  - ``RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS``
+
+    Since v16.04, the vhost library forwards checksum and gso requests for
+    packets received from a virtio driver by filling Tx offload metadata in
+    the mbuf. This behavior is inconsistent with other drivers but it is left
+    untouched for existing applications that might rely on it.
+
+    This flag disables the legacy behavior and instead ask vhost to simply
+    populate Rx offload metadata in the mbuf.
+
+    It is disabled by default.
+
 * ``rte_vhost_driver_set_features(path, features)``
 
   This function sets the feature bits the vhost-user driver supports. The

doc/guides/rel_notes/release_21_05.rst

@@ -343,6 +343,12 @@ API Changes
   ``policer_action_recolor_supported`` and ``policer_action_drop_supported``
   have been removed.
 
+* vhost: The vhost library currently populates received mbufs from a virtio
+  driver with Tx offload flags while not filling Rx offload flags.
+  While this behavior is arguable, it is kept untouched.
+  A new flag ``RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS`` has been added to ask
+  for a behavior compliant with the mbuf offload API.
+
 * stack: Lock-free ``rte_stack`` no longer silently ignores push and pop when
   it's not supported on the current platform. Instead ``rte_stack_create()``
   fails and ``rte_errno`` is set to ``ENOTSUP``.

drivers/net/vhost/rte_eth_vhost.c

@@ -1505,7 +1505,7 @@ rte_pmd_vhost_probe(struct rte_vdev_device *dev)
 	int ret = 0;
 	char *iface_name;
 	uint16_t queues;
-	uint64_t flags = 0;
+	uint64_t flags = RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS;
 	uint64_t disable_flags = 0;
 	int client_mode = 0;
 	int iommu_support = 0;

examples/vhost/main.c

@@ -19,6 +19,7 @@
 #include <rte_log.h>
 #include <rte_string_fns.h>
 #include <rte_malloc.h>
+#include <rte_net.h>
 #include <rte_vhost.h>
 #include <rte_ip.h>
 #include <rte_tcp.h>
@@ -1029,33 +1030,34 @@ find_local_dest(struct vhost_dev *vdev, struct rte_mbuf *m,
 	return 0;
 }
 
-static uint16_t
-get_psd_sum(void *l3_hdr, uint64_t ol_flags)
-{
-	if (ol_flags & PKT_TX_IPV4)
-		return rte_ipv4_phdr_cksum(l3_hdr, ol_flags);
-	else /* assume ethertype == RTE_ETHER_TYPE_IPV6 */
-		return rte_ipv6_phdr_cksum(l3_hdr, ol_flags);
-}
-
 static void virtio_tx_offload(struct rte_mbuf *m)
 {
+	struct rte_net_hdr_lens hdr_lens;
+	struct rte_ipv4_hdr *ipv4_hdr;
+	struct rte_tcp_hdr *tcp_hdr;
+	uint32_t ptype;
 	void *l3_hdr;
-	struct rte_ipv4_hdr *ipv4_hdr = NULL;
-	struct rte_tcp_hdr *tcp_hdr = NULL;
-	struct rte_ether_hdr *eth_hdr =
-		rte_pktmbuf_mtod(m, struct rte_ether_hdr *);
 
-	l3_hdr = (char *)eth_hdr + m->l2_len;
+	ptype = rte_net_get_ptype(m, &hdr_lens, RTE_PTYPE_ALL_MASK);
+	m->l2_len = hdr_lens.l2_len;
+	m->l3_len = hdr_lens.l3_len;
+	m->l4_len = hdr_lens.l4_len;
 
-	if (m->ol_flags & PKT_TX_IPV4) {
+	l3_hdr = rte_pktmbuf_mtod_offset(m, void *, m->l2_len);
+	tcp_hdr = rte_pktmbuf_mtod_offset(m, struct rte_tcp_hdr *,
+		m->l2_len + m->l3_len);
+
+	m->ol_flags |= PKT_TX_TCP_SEG;
+	if ((ptype & RTE_PTYPE_L3_MASK) == RTE_PTYPE_L3_IPV4) {
+		m->ol_flags |= PKT_TX_IPV4;
+		m->ol_flags |= PKT_TX_IP_CKSUM;
 		ipv4_hdr = l3_hdr;
 		ipv4_hdr->hdr_checksum = 0;
-		m->ol_flags |= PKT_TX_IP_CKSUM;
+		tcp_hdr->cksum = rte_ipv4_phdr_cksum(l3_hdr, m->ol_flags);
+	} else { /* assume ethertype == RTE_ETHER_TYPE_IPV6 */
+		m->ol_flags |= PKT_TX_IPV6;
+		tcp_hdr->cksum = rte_ipv6_phdr_cksum(l3_hdr, m->ol_flags);
 	}
-
-	tcp_hdr = (struct rte_tcp_hdr *)((char *)l3_hdr + m->l3_len);
-	tcp_hdr->cksum = get_psd_sum(l3_hdr, m->ol_flags);
 }
 
 static __rte_always_inline void
@@ -1148,7 +1150,7 @@ queue2nic:
 		m->vlan_tci = vlan_tag;
 	}
 
-	if (m->ol_flags & PKT_TX_TCP_SEG)
+	if (m->ol_flags & PKT_RX_LRO)
 		virtio_tx_offload(m);
 
 	tx_q->m_table[tx_q->len++] = m;
@@ -1633,7 +1635,7 @@ main(int argc, char *argv[])
 	int ret, i;
 	uint16_t portid;
 	static pthread_t tid;
-	uint64_t flags = 0;
+	uint64_t flags = RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS;
 
 	signal(SIGINT, sigint_handler);
 

lib/vhost/rte_vhost.h

@@ -36,6 +36,7 @@ extern "C" {
 /* support only linear buffers (no chained mbufs) */
 #define RTE_VHOST_USER_LINEARBUF_SUPPORT	(1ULL << 6)
 #define RTE_VHOST_USER_ASYNC_COPY	(1ULL << 7)
+#define RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS	(1ULL << 8)
 
 /* Features. */
 #ifndef VIRTIO_NET_F_GUEST_ANNOUNCE

lib/vhost/socket.c

@@ -42,6 +42,7 @@ struct vhost_user_socket {
 	bool extbuf;
 	bool linearbuf;
 	bool async_copy;
+	bool net_compliant_ol_flags;
 
 	/*
 	 * The "supported_features" indicates the feature bits the
@@ -224,7 +225,8 @@ vhost_user_add_connection(int fd, struct vhost_user_socket *vsocket)
 	size = strnlen(vsocket->path, PATH_MAX);
 	vhost_set_ifname(vid, vsocket->path, size);
 
-	vhost_set_builtin_virtio_net(vid, vsocket->use_builtin_virtio_net);
+	vhost_setup_virtio_net(vid, vsocket->use_builtin_virtio_net,
+		vsocket->net_compliant_ol_flags);
 
 	vhost_attach_vdpa_device(vid, vsocket->vdpa_dev);
 
@@ -877,6 +879,7 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
 	vsocket->extbuf = flags & RTE_VHOST_USER_EXTBUF_SUPPORT;
 	vsocket->linearbuf = flags & RTE_VHOST_USER_LINEARBUF_SUPPORT;
 	vsocket->async_copy = flags & RTE_VHOST_USER_ASYNC_COPY;
+	vsocket->net_compliant_ol_flags = flags & RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS;
 
 	if (vsocket->async_copy &&
 		(flags & (RTE_VHOST_USER_IOMMU_SUPPORT |

lib/vhost/vhost.c

@@ -752,7 +752,7 @@ vhost_set_ifname(int vid, const char *if_name, unsigned int if_len)
 }
 
 void
-vhost_set_builtin_virtio_net(int vid, bool enable)
+vhost_setup_virtio_net(int vid, bool enable, bool compliant_ol_flags)
 {
 	struct virtio_net *dev = get_device(vid);
 
@@ -763,6 +763,10 @@ vhost_set_builtin_virtio_net(int vid, bool enable)
 		dev->flags |= VIRTIO_DEV_BUILTIN_VIRTIO_NET;
 	else
 		dev->flags &= ~VIRTIO_DEV_BUILTIN_VIRTIO_NET;
+	if (!compliant_ol_flags)
+		dev->flags |= VIRTIO_DEV_LEGACY_OL_FLAGS;
+	else
+		dev->flags &= ~VIRTIO_DEV_LEGACY_OL_FLAGS;
 }
 
 void

lib/vhost/vhost.h

@@ -27,15 +27,17 @@
 #include "rte_vhost_async.h"
 
 /* Used to indicate that the device is running on a data core */
-#define VIRTIO_DEV_RUNNING 1
+#define VIRTIO_DEV_RUNNING ((uint32_t)1 << 0)
 /* Used to indicate that the device is ready to operate */
-#define VIRTIO_DEV_READY 2
+#define VIRTIO_DEV_READY ((uint32_t)1 << 1)
 /* Used to indicate that the built-in vhost net device backend is enabled */
-#define VIRTIO_DEV_BUILTIN_VIRTIO_NET 4
+#define VIRTIO_DEV_BUILTIN_VIRTIO_NET ((uint32_t)1 << 2)
 /* Used to indicate that the device has its own data path and configured */
-#define VIRTIO_DEV_VDPA_CONFIGURED 8
+#define VIRTIO_DEV_VDPA_CONFIGURED ((uint32_t)1 << 3)
 /* Used to indicate that the feature negotiation failed */
-#define VIRTIO_DEV_FEATURES_FAILED 16
+#define VIRTIO_DEV_FEATURES_FAILED ((uint32_t)1 << 4)
+/* Used to indicate that the virtio_net tx code should fill TX ol_flags */
+#define VIRTIO_DEV_LEGACY_OL_FLAGS ((uint32_t)1 << 5)
 
 /* Backend value set by guest. */
 #define VIRTIO_DEV_STOPPED -1
@@ -683,7 +685,7 @@ int alloc_vring_queue(struct virtio_net *dev, uint32_t vring_idx);
 void vhost_attach_vdpa_device(int vid, struct rte_vdpa_device *dev);
 
 void vhost_set_ifname(int, const char *if_name, unsigned int if_len);
-void vhost_set_builtin_virtio_net(int vid, bool enable);
+void vhost_setup_virtio_net(int vid, bool enable, bool legacy_ol_flags);
 void vhost_enable_extbuf(int vid);
 void vhost_enable_linearbuf(int vid);
 int vhost_enable_guest_notification(struct virtio_net *dev,

lib/vhost/virtio_net.c

@@ -8,6 +8,7 @@
 
 #include <rte_mbuf.h>
 #include <rte_memcpy.h>
+#include <rte_net.h>
 #include <rte_ether.h>
 #include <rte_ip.h>
 #include <rte_vhost.h>
@@ -2303,15 +2304,12 @@ parse_ethernet(struct rte_mbuf *m, uint16_t *l4_proto, void **l4_hdr)
 }
 
 static __rte_always_inline void
-vhost_dequeue_offload(struct virtio_net_hdr *hdr, struct rte_mbuf *m)
+vhost_dequeue_offload_legacy(struct virtio_net_hdr *hdr, struct rte_mbuf *m)
 {
 	uint16_t l4_proto = 0;
 	void *l4_hdr = NULL;
 	struct rte_tcp_hdr *tcp_hdr = NULL;
 
-	if (hdr->flags == 0 && hdr->gso_type == VIRTIO_NET_HDR_GSO_NONE)
-		return;
-
 	parse_ethernet(m, &l4_proto, &l4_hdr);
 	if (hdr->flags == VIRTIO_NET_HDR_F_NEEDS_CSUM) {
 		if (hdr->csum_start == (m->l2_len + m->l3_len)) {
@@ -2356,6 +2354,94 @@ vhost_dequeue_offload(struct virtio_net_hdr *hdr, struct rte_mbuf *m)
 	}
 }
 
+static __rte_always_inline void
+vhost_dequeue_offload(struct virtio_net_hdr *hdr, struct rte_mbuf *m,
+	bool legacy_ol_flags)
+{
+	struct rte_net_hdr_lens hdr_lens;
+	int l4_supported = 0;
+	uint32_t ptype;
+
+	if (hdr->flags == 0 && hdr->gso_type == VIRTIO_NET_HDR_GSO_NONE)
+		return;
+
+	if (legacy_ol_flags) {
+		vhost_dequeue_offload_legacy(hdr, m);
+		return;
+	}
+
+	m->ol_flags |= PKT_RX_IP_CKSUM_UNKNOWN;
+
+	ptype = rte_net_get_ptype(m, &hdr_lens, RTE_PTYPE_ALL_MASK);
+	m->packet_type = ptype;
+	if ((ptype & RTE_PTYPE_L4_MASK) == RTE_PTYPE_L4_TCP ||
+	    (ptype & RTE_PTYPE_L4_MASK) == RTE_PTYPE_L4_UDP ||
+	    (ptype & RTE_PTYPE_L4_MASK) == RTE_PTYPE_L4_SCTP)
+		l4_supported = 1;
+
+	/* According to Virtio 1.1 spec, the device only needs to look at
+	 * VIRTIO_NET_HDR_F_NEEDS_CSUM in the packet transmission path.
+	 * This differs from the processing incoming packets path where the
+	 * driver could rely on VIRTIO_NET_HDR_F_DATA_VALID flag set by the
+	 * device.
+	 *
+	 * 5.1.6.2.1 Driver Requirements: Packet Transmission
+	 * The driver MUST NOT set the VIRTIO_NET_HDR_F_DATA_VALID and
+	 * VIRTIO_NET_HDR_F_RSC_INFO bits in flags.
+	 *
+	 * 5.1.6.2.2 Device Requirements: Packet Transmission
+	 * The device MUST ignore flag bits that it does not recognize.
+	 */
+	if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
+		uint32_t hdrlen;
+
+		hdrlen = hdr_lens.l2_len + hdr_lens.l3_len + hdr_lens.l4_len;
+		if (hdr->csum_start <= hdrlen && l4_supported != 0) {
+			m->ol_flags |= PKT_RX_L4_CKSUM_NONE;
+		} else {
+			/* Unknown proto or tunnel, do sw cksum. We can assume
+			 * the cksum field is in the first segment since the
+			 * buffers we provided to the host are large enough.
+			 * In case of SCTP, this will be wrong since it's a CRC
+			 * but there's nothing we can do.
+			 */
+			uint16_t csum = 0, off;
+
+			if (rte_raw_cksum_mbuf(m, hdr->csum_start,
+					rte_pktmbuf_pkt_len(m) - hdr->csum_start, &csum) < 0)
+				return;
+			if (likely(csum != 0xffff))
+				csum = ~csum;
+			off = hdr->csum_offset + hdr->csum_start;
+			if (rte_pktmbuf_data_len(m) >= off + 1)
+				*rte_pktmbuf_mtod_offset(m, uint16_t *, off) = csum;
+		}
+	}
+
+	if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
+		if (hdr->gso_size == 0)
+			return;
+
+		switch (hdr->gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
+		case VIRTIO_NET_HDR_GSO_TCPV4:
+		case VIRTIO_NET_HDR_GSO_TCPV6:
+			if ((ptype & RTE_PTYPE_L4_MASK) != RTE_PTYPE_L4_TCP)
+				break;
+			m->ol_flags |= PKT_RX_LRO | PKT_RX_L4_CKSUM_NONE;
+			m->tso_segsz = hdr->gso_size;
+			break;
+		case VIRTIO_NET_HDR_GSO_UDP:
+			if ((ptype & RTE_PTYPE_L4_MASK) != RTE_PTYPE_L4_UDP)
+				break;
+			m->ol_flags |= PKT_RX_LRO | PKT_RX_L4_CKSUM_NONE;
+			m->tso_segsz = hdr->gso_size;
+			break;
+		default:
+			break;
+		}
+	}
+}
+
 static __rte_noinline void
 copy_vnet_hdr_from_desc(struct virtio_net_hdr *hdr,
 		struct buf_vector *buf_vec)
@@ -2380,7 +2466,8 @@ copy_vnet_hdr_from_desc(struct virtio_net_hdr *hdr,
 static __rte_always_inline int
 copy_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
 		  struct buf_vector *buf_vec, uint16_t nr_vec,
-		  struct rte_mbuf *m, struct rte_mempool *mbuf_pool)
+		  struct rte_mbuf *m, struct rte_mempool *mbuf_pool,
+		  bool legacy_ol_flags)
 {
 	uint32_t buf_avail, buf_offset;
 	uint64_t buf_addr, buf_len;
@@ -2513,7 +2600,7 @@ copy_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	m->pkt_len    += mbuf_offset;
 
 	if (hdr)
-		vhost_dequeue_offload(hdr, m);
+		vhost_dequeue_offload(hdr, m, legacy_ol_flags);
 
 out:
 
@@ -2606,9 +2693,11 @@ virtio_dev_pktmbuf_alloc(struct virtio_net *dev, struct rte_mempool *mp,
 	return pkt;
 }
 
-static __rte_noinline uint16_t
+__rte_always_inline
+static uint16_t
 virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
-	struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts, uint16_t count)
+	struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts, uint16_t count,
+	bool legacy_ol_flags)
 {
 	uint16_t i;
 	uint16_t free_entries;
@@ -2668,7 +2757,7 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
 		}
 
 		err = copy_desc_to_mbuf(dev, vq, buf_vec, nr_vec, pkts[i],
-				mbuf_pool);
+				mbuf_pool, legacy_ol_flags);
 		if (unlikely(err)) {
 			rte_pktmbuf_free(pkts[i]);
 			if (!allocerr_warned) {
@@ -2696,6 +2785,24 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	return (i - dropped);
 }
 
+__rte_noinline
+static uint16_t
+virtio_dev_tx_split_legacy(struct virtio_net *dev,
+	struct vhost_virtqueue *vq, struct rte_mempool *mbuf_pool,
+	struct rte_mbuf **pkts, uint16_t count)
+{
+	return virtio_dev_tx_split(dev, vq, mbuf_pool, pkts, count, true);
+}
+
+__rte_noinline
+static uint16_t
+virtio_dev_tx_split_compliant(struct virtio_net *dev,
+	struct vhost_virtqueue *vq, struct rte_mempool *mbuf_pool,
+	struct rte_mbuf **pkts, uint16_t count)
+{
+	return virtio_dev_tx_split(dev, vq, mbuf_pool, pkts, count, false);
+}
+
 static __rte_always_inline int
 vhost_reserve_avail_batch_packed(struct virtio_net *dev,
 				 struct vhost_virtqueue *vq,
@@ -2770,7 +2877,8 @@ err:
 static __rte_always_inline int
 virtio_dev_tx_batch_packed(struct virtio_net *dev,
 			   struct vhost_virtqueue *vq,
-			   struct rte_mbuf **pkts)
+			   struct rte_mbuf **pkts,
+			   bool legacy_ol_flags)
 {
 	uint16_t avail_idx = vq->last_avail_idx;
 	uint32_t buf_offset = sizeof(struct virtio_net_hdr_mrg_rxbuf);
@@ -2794,7 +2902,7 @@ virtio_dev_tx_batch_packed(struct virtio_net *dev,
 	if (virtio_net_with_host_offload(dev)) {
 		vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
 			hdr = (struct virtio_net_hdr *)(desc_addrs[i]);
-			vhost_dequeue_offload(hdr, pkts[i]);
+			vhost_dequeue_offload(hdr, pkts[i], legacy_ol_flags);
 		}
 	}
 
@@ -2815,7 +2923,8 @@ vhost_dequeue_single_packed(struct virtio_net *dev,
 			    struct rte_mempool *mbuf_pool,
 			    struct rte_mbuf *pkts,
 			    uint16_t *buf_id,
-			    uint16_t *desc_count)
+			    uint16_t *desc_count,
+			    bool legacy_ol_flags)
 {
 	struct buf_vector buf_vec[BUF_VECTOR_MAX];
 	uint32_t buf_len;
@@ -2841,7 +2950,7 @@ vhost_dequeue_single_packed(struct virtio_net *dev,
 	}
 
 	err = copy_desc_to_mbuf(dev, vq, buf_vec, nr_vec, pkts,
-				mbuf_pool);
+				mbuf_pool, legacy_ol_flags);
 	if (unlikely(err)) {
 		if (!allocerr_warned) {
 			VHOST_LOG_DATA(ERR,
@@ -2859,14 +2968,15 @@ static __rte_always_inline int
 virtio_dev_tx_single_packed(struct virtio_net *dev,
 			    struct vhost_virtqueue *vq,
 			    struct rte_mempool *mbuf_pool,
-			    struct rte_mbuf *pkts)
+			    struct rte_mbuf *pkts,
+			    bool legacy_ol_flags)
 {
 
 	uint16_t buf_id, desc_count = 0;
 	int ret;
 
 	ret = vhost_dequeue_single_packed(dev, vq, mbuf_pool, pkts, &buf_id,
-					&desc_count);
+					&desc_count, legacy_ol_flags);
 
 	if (likely(desc_count > 0)) {
 		if (virtio_net_is_inorder(dev))
@@ -2882,12 +2992,14 @@ virtio_dev_tx_single_packed(struct virtio_net *dev,
 	return ret;
 }
 
-static __rte_noinline uint16_t
+__rte_always_inline
+static uint16_t
 virtio_dev_tx_packed(struct virtio_net *dev,
 		     struct vhost_virtqueue *__rte_restrict vq,
 		     struct rte_mempool *mbuf_pool,
 		     struct rte_mbuf **__rte_restrict pkts,
-		     uint32_t count)
+		     uint32_t count,
+		     bool legacy_ol_flags)
 {
 	uint32_t pkt_idx = 0;
 
@@ -2899,14 +3011,16 @@ virtio_dev_tx_packed(struct virtio_net *dev,
 
 		if (count - pkt_idx >= PACKED_BATCH_SIZE) {
 			if (!virtio_dev_tx_batch_packed(dev, vq,
-							&pkts[pkt_idx])) {
+							&pkts[pkt_idx],
+							legacy_ol_flags)) {
 				pkt_idx += PACKED_BATCH_SIZE;
 				continue;
 			}
 		}
 
 		if (virtio_dev_tx_single_packed(dev, vq, mbuf_pool,
-						pkts[pkt_idx]))
+						pkts[pkt_idx],
+						legacy_ol_flags))
 			break;
 		pkt_idx++;
 	} while (pkt_idx < count);
@@ -2924,6 +3038,24 @@ virtio_dev_tx_packed(struct virtio_net *dev,
 	return pkt_idx;
 }
 
+__rte_noinline
+static uint16_t
+virtio_dev_tx_packed_legacy(struct virtio_net *dev,
+	struct vhost_virtqueue *__rte_restrict vq, struct rte_mempool *mbuf_pool,
+	struct rte_mbuf **__rte_restrict pkts, uint32_t count)
+{
+	return virtio_dev_tx_packed(dev, vq, mbuf_pool, pkts, count, true);
+}
+
+__rte_noinline
+static uint16_t
+virtio_dev_tx_packed_compliant(struct virtio_net *dev,
+	struct vhost_virtqueue *__rte_restrict vq, struct rte_mempool *mbuf_pool,
+	struct rte_mbuf **__rte_restrict pkts, uint32_t count)
+{
+	return virtio_dev_tx_packed(dev, vq, mbuf_pool, pkts, count, false);
+}
+
 uint16_t
 rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
 	struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts, uint16_t count)
@@ -2999,10 +3131,17 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
 		count -= 1;
 	}
 
-	if (vq_is_packed(dev))
+	if (vq_is_packed(dev)) {
-		count = virtio_dev_tx_packed(dev, vq, mbuf_pool, pkts, count);
+		if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
-	else
+			count = virtio_dev_tx_packed_legacy(dev, vq, mbuf_pool, pkts, count);
-		count = virtio_dev_tx_split(dev, vq, mbuf_pool, pkts, count);
+		else
+			count = virtio_dev_tx_packed_compliant(dev, vq, mbuf_pool, pkts, count);
+	} else {
+		if (dev->flags & VIRTIO_DEV_LEGACY_OL_FLAGS)
+			count = virtio_dev_tx_split_legacy(dev, vq, mbuf_pool, pkts, count);
+		else
+			count = virtio_dev_tx_split_compliant(dev, vq, mbuf_pool, pkts, count);
+	}
 
 out:
 	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))