[dpdk-dev] [PATCH v3 3/3] 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>
---
 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   | 16 ++++++------
 drivers/net/virtio/virtqueue.h     | 41 ++++++++++++++++++++++++------
 5 files changed, 52 insertions(+), 17 deletions(-)

diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
index 446c338fc..6d461180c 100644
--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c
@@ -1613,6 +1613,8 @@ 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 f8d8a56ab..b8aab7da4 100644
--- a/drivers/net/virtio/virtio_ethdev.h
+++ b/drivers/net/virtio/virtio_ethdev.h
@@ -35,7 +35,8 @@
 	 1ULL << VIRTIO_F_VERSION_1       |	\
 	 1ULL << VIRTIO_F_IN_ORDER        |	\
 	 1ULL << VIRTIO_F_RING_PACKED	  |	\
-	 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 b22b62dad..38a0261da 100644
--- a/drivers/net/virtio/virtio_pci.h
+++ b/drivers/net/virtio/virtio_pci.h
@@ -129,6 +129,12 @@ 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
@@ -241,6 +247,7 @@ 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 2309b71d6..ebb86ef70 100644
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -1152,7 +1152,7 @@ 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))
@@ -1361,7 +1361,7 @@ virtio_recv_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);
 
@@ -1549,7 +1549,7 @@ 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);
 
@@ -1940,7 +1940,7 @@ virtio_xmit_pkts_packed(void *tx_queue, struct rte_mbuf **tx_pkts,
 
 		/* Positive value indicates it need free vring descriptors */
 		if (unlikely(need > 0)) {
-			virtio_rmb();
+			virtio_rmb(hw->weak_barriers);
 			need = RTE_MIN(need, (int)nb_pkts);
 			virtio_xmit_cleanup_packed(vq, need);
 			need = slots - vq->vq_free_cnt;
@@ -1988,7 +1988,7 @@ 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);
 
@@ -2030,7 +2030,7 @@ 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);
@@ -2086,7 +2086,7 @@ 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);
 
@@ -2134,7 +2134,7 @@ 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 53aeac238..123bec34f 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)
@@ -325,7 +350,7 @@ virtqueue_enable_intr_packed(struct virtqueue *vq)
 
 
 	if (vq->event_flags_shadow == RING_EVENT_FLAGS_DISABLE) {
-		virtio_wmb();
+		virtio_wmb(vq->hw->weak_barriers);
 		vq->event_flags_shadow = RING_EVENT_FLAGS_ENABLE;
 		*event_flags = vq->event_flags_shadow;
 	}
@@ -391,7 +416,7 @@ 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;
 }
 
@@ -419,7 +444,7 @@ virtqueue_kick_prepare(struct virtqueue *vq)
 	 * Ensure updated avail->idx is visible to vhost before reading
 	 * the used->flags.
 	 */
-	virtio_mb();
+	virtio_mb(vq->hw->weak_barriers);
 	return !(vq->vq_ring.used->flags & VRING_USED_F_NO_NOTIFY);
 }
 
@@ -431,7 +456,7 @@ virtqueue_kick_prepare_packed(struct virtqueue *vq)
 	/*
 	 * Ensure updated data is visible to vhost before reading the flags.
 	 */
-	virtio_mb();
+	virtio_mb(vq->hw->weak_barriers);
 	flags = vq->ring_packed.device_event->desc_event_flags;
 
 	return flags != RING_EVENT_FLAGS_DISABLE;
-- 
2.17.1