[dpdk-dev] [PATCH] net/virtio: add platform memory ordering feature support

[Ilya Maximets <i.maximets@samsung.com>]

VIRTIO_F_ORDER_PLATFORM is required to use proper memory barriers
in case of HW vhost implementations like vDPA.

DMA barriers (rte_cio_*) are sufficent for that purpose.

Previously known as VIRTIO_F_IO_BARRIER.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
---

Based on "[RFC] net/virtio: use real barriers for vDPA".

RFC --> PATCH:
  * Dropped vendor-specific hack to determine if we need real barriers.
  * Added VIRTIO_F_ORDER_PLATFORM feature definition and checking.

Note: Patch to change the name of the feature from VIRTIO_F_IO_BARRIER
      to VIRTIO_F_ORDER_PLATFORM is not merged yet:
      https://www.mail-archive.com/virtio-dev@lists.oasis-open.org/msg04114.html

 drivers/net/virtio/virtio_ethdev.c |  2 ++
 drivers/net/virtio/virtio_ethdev.h |  3 ++-
 drivers/net/virtio/virtio_pci.h    |  7 ++++++
 drivers/net/virtio/virtio_rxtx.c   | 14 ++++++------
 drivers/net/virtio/virtqueue.h     | 35 +++++++++++++++++++++++++-----
 5 files changed, 48 insertions(+), 13 deletions(-)

diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
index cb2b2e0bf..5ae7a9650 100644
--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c
@@ -1474,6 +1474,8 @@ virtio_init_device(struct rte_eth_dev *eth_dev, uint64_t req_features)
 	if (virtio_negotiate_features(hw, req_features) < 0)
 		return -1;
 
+	hw->weak_barriers = !vtpci_with_feature(hw, VIRTIO_F_ORDER_PLATFORM);
+
 	if (!hw->virtio_user_dev) {
 		pci_dev = RTE_ETH_DEV_TO_PCI(eth_dev);
 		rte_eth_copy_pci_info(eth_dev, pci_dev);
diff --git a/drivers/net/virtio/virtio_ethdev.h b/drivers/net/virtio/virtio_ethdev.h
index e0f80e5a4..c098e5ac0 100644
--- a/drivers/net/virtio/virtio_ethdev.h
+++ b/drivers/net/virtio/virtio_ethdev.h
@@ -34,7 +34,8 @@
 	 1u << VIRTIO_RING_F_INDIRECT_DESC |    \
 	 1ULL << VIRTIO_F_VERSION_1       |	\
 	 1ULL << VIRTIO_F_IN_ORDER        |	\
-	 1ULL << VIRTIO_F_IOMMU_PLATFORM)
+	 1ULL << VIRTIO_F_IOMMU_PLATFORM  |	\
+	 1ULL << VIRTIO_F_ORDER_PLATFORM)
 
 #define VIRTIO_PMD_SUPPORTED_GUEST_FEATURES	\
 	(VIRTIO_PMD_DEFAULT_GUEST_FEATURES |	\
diff --git a/drivers/net/virtio/virtio_pci.h b/drivers/net/virtio/virtio_pci.h
index e961a58ca..e2f096185 100644
--- a/drivers/net/virtio/virtio_pci.h
+++ b/drivers/net/virtio/virtio_pci.h
@@ -128,6 +128,12 @@ struct virtnet_ctl;
  */
 #define VIRTIO_F_IN_ORDER 35
 
+/*
+ * This feature indicates that memory accesses by the driver and the device
+ * are ordered in a way described by the platform.
+ */
+#define VIRTIO_F_ORDER_PLATFORM 36
+
 /* The Guest publishes the used index for which it expects an interrupt
  * at the end of the avail ring. Host should ignore the avail->flags field. */
 /* The Host publishes the avail index for which it expects a kick
@@ -240,6 +246,7 @@ struct virtio_hw {
 	uint8_t     use_simple_rx;
 	uint8_t     use_inorder_rx;
 	uint8_t     use_inorder_tx;
+	uint8_t     weak_barriers;
 	bool        has_tx_offload;
 	bool        has_rx_offload;
 	uint16_t    port_id;
diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
index cb8f89f18..66195bf47 100644
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -906,7 +906,7 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts, uint16_t nb_pkts)
 
 	nb_used = VIRTQUEUE_NUSED(vq);
 
-	virtio_rmb();
+	virtio_rmb(hw->weak_barriers);
 
 	num = likely(nb_used <= nb_pkts) ? nb_used : nb_pkts;
 	if (unlikely(num > VIRTIO_MBUF_BURST_SZ))
@@ -1017,7 +1017,7 @@ virtio_recv_mergeable_pkts_inorder(void *rx_queue,
 	nb_used = RTE_MIN(nb_used, nb_pkts);
 	nb_used = RTE_MIN(nb_used, VIRTIO_MBUF_BURST_SZ);
 
-	virtio_rmb();
+	virtio_rmb(hw->weak_barriers);
 
 	PMD_RX_LOG(DEBUG, "used:%d", nb_used);
 
@@ -1202,7 +1202,7 @@ virtio_recv_mergeable_pkts(void *rx_queue,
 
 	nb_used = VIRTQUEUE_NUSED(vq);
 
-	virtio_rmb();
+	virtio_rmb(hw->weak_barriers);
 
 	PMD_RX_LOG(DEBUG, "used:%d", nb_used);
 
@@ -1365,7 +1365,7 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 	PMD_TX_LOG(DEBUG, "%d packets to xmit", nb_pkts);
 	nb_used = VIRTQUEUE_NUSED(vq);
 
-	virtio_rmb();
+	virtio_rmb(hw->weak_barriers);
 	if (likely(nb_used > vq->vq_nentries - vq->vq_free_thresh))
 		virtio_xmit_cleanup(vq, nb_used);
 
@@ -1407,7 +1407,7 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 		/* Positive value indicates it need free vring descriptors */
 		if (unlikely(need > 0)) {
 			nb_used = VIRTQUEUE_NUSED(vq);
-			virtio_rmb();
+			virtio_rmb(hw->weak_barriers);
 			need = RTE_MIN(need, (int)nb_used);
 
 			virtio_xmit_cleanup(vq, need);
@@ -1463,7 +1463,7 @@ virtio_xmit_pkts_inorder(void *tx_queue,
 	PMD_TX_LOG(DEBUG, "%d packets to xmit", nb_pkts);
 	nb_used = VIRTQUEUE_NUSED(vq);
 
-	virtio_rmb();
+	virtio_rmb(hw->weak_barriers);
 	if (likely(nb_used > vq->vq_nentries - vq->vq_free_thresh))
 		virtio_xmit_cleanup_inorder(vq, nb_used);
 
@@ -1511,7 +1511,7 @@ virtio_xmit_pkts_inorder(void *tx_queue,
 		need = slots - vq->vq_free_cnt;
 		if (unlikely(need > 0)) {
 			nb_used = VIRTQUEUE_NUSED(vq);
-			virtio_rmb();
+			virtio_rmb(hw->weak_barriers);
 			need = RTE_MIN(need, (int)nb_used);
 
 			virtio_xmit_cleanup_inorder(vq, need);
diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
index 26518ed98..6b9055a1f 100644
--- a/drivers/net/virtio/virtqueue.h
+++ b/drivers/net/virtio/virtqueue.h
@@ -19,15 +19,40 @@
 struct rte_mbuf;
 
 /*
- * Per virtio_config.h in Linux.
+ * Per virtio_ring.h in Linux.
  *     For virtio_pci on SMP, we don't need to order with respect to MMIO
  *     accesses through relaxed memory I/O windows, so smp_mb() et al are
  *     sufficient.
  *
+ *     For using virtio to talk to real devices (eg. vDPA) we do need real
+ *     barriers.
  */
-#define virtio_mb()	rte_smp_mb()
-#define virtio_rmb()	rte_smp_rmb()
-#define virtio_wmb()	rte_smp_wmb()
+static inline void
+virtio_mb(uint8_t weak_barriers)
+{
+	if (weak_barriers)
+		rte_smp_mb();
+	else
+		rte_mb();
+}
+
+static inline void
+virtio_rmb(uint8_t weak_barriers)
+{
+	if (weak_barriers)
+		rte_smp_rmb();
+	else
+		rte_cio_rmb();
+}
+
+static inline void
+virtio_wmb(uint8_t weak_barriers)
+{
+	if (weak_barriers)
+		rte_smp_wmb();
+	else
+		rte_cio_wmb();
+}
 
 #ifdef RTE_PMD_PACKET_PREFETCH
 #define rte_packet_prefetch(p)  rte_prefetch1(p)
@@ -312,7 +337,7 @@ void vq_ring_free_inorder(struct virtqueue *vq, uint16_t desc_idx,
 static inline void
 vq_update_avail_idx(struct virtqueue *vq)
 {
-	virtio_wmb();
+	virtio_wmb(vq->hw->weak_barriers);
 	vq->vq_ring.avail->idx = vq->vq_avail_idx;
 }
 
-- 
2.17.1