svn commit: r361758 - in head/sys/dev: netmap virtio/network

[Vincenzo Maffione]

Author: vmaffione
Date: Wed Jun  3 17:42:17 2020
New Revision: 361758
URL: https://svnweb.freebsd.org/changeset/base/361758

Log:
  netmap: vtnet: add vtnrx_nm_refill index to receive queues
  
  The new index tracks the next netmap slot that is going
  to be enqueued into the virtqueue. The index is necessary
  to prevent the receive VQ and the netmap rx ring from going
  out of sync, considering that we never enqueue N slots, but
  at most N-1. This change fixes a bug that causes the VQ
  and the netmap ring to go out of sync after N-1 packets
  have been received.
  
  MFC after:	1 week

Modified:
  head/sys/dev/netmap/if_vtnet_netmap.h
  head/sys/dev/virtio/network/if_vtnetvar.h

Modified: head/sys/dev/netmap/if_vtnet_netmap.h
==============================================================================
--- head/sys/dev/netmap/if_vtnet_netmap.h	Wed Jun  3 17:26:00 2020	(r361757)
+++ head/sys/dev/netmap/if_vtnet_netmap.h	Wed Jun  3 17:42:17 2020	(r361758)
@@ -196,9 +196,11 @@ vtnet_netmap_txsync(struct netmap_kring *kring, int fl
 }
 
 /*
- * Publish (up to) num netmap receive buffers to the host,
- * starting from the first one that the user made available
- * (kring->nr_hwcur).
+ * Publish 'num 'netmap receive buffers to the host, starting
+ * from the next available one (rx->vtnrx_nm_refill).
+ * Return a positive error code on error, and 0 on success.
+ * If we could not publish all of the buffers that's an error,
+ * since the netmap ring and the virtqueue would go out of sync.
  */
 static int
 vtnet_netmap_kring_refill(struct netmap_kring *kring, u_int num)
@@ -208,7 +210,7 @@ vtnet_netmap_kring_refill(struct netmap_kring *kring, 
 	struct netmap_ring *ring = kring->ring;
 	u_int ring_nr = kring->ring_id;
 	u_int const lim = kring->nkr_num_slots - 1;
-	u_int nm_i = kring->nr_hwcur;
+	u_int nm_i;
 
 	/* device-specific */
 	struct vtnet_softc *sc = ifp->if_softc;
@@ -219,7 +221,8 @@ vtnet_netmap_kring_refill(struct netmap_kring *kring, 
 	struct sglist_seg ss[2];
 	struct sglist sg = { ss, 0, 0, 2 };
 
-	for (; num > 0; nm_i = nm_next(nm_i, lim), num--) {
+	for (nm_i = rxq->vtnrx_nm_refill; num > 0;
+	    nm_i = nm_next(nm_i, lim), num--) {
 		struct netmap_slot *slot = &ring->slot[nm_i];
 		uint64_t paddr;
 		void *addr = PNMB(na, slot, &paddr);
@@ -227,7 +230,7 @@ vtnet_netmap_kring_refill(struct netmap_kring *kring, 
 
 		if (addr == NETMAP_BUF_BASE(na)) { /* bad buf */
 			if (netmap_ring_reinit(kring))
-				return -1;
+				return EFAULT;
 		}
 
 		slot->flags &= ~NS_BUF_CHANGED;
@@ -240,14 +243,14 @@ vtnet_netmap_kring_refill(struct netmap_kring *kring, 
 		err = virtqueue_enqueue(vq, /*cookie=*/rxq, &sg,
 				/*readable=*/0, /*writeable=*/sg.sg_nseg);
 		if (unlikely(err)) {
-			if (err != ENOSPC)
-				nm_prerr("virtqueue_enqueue(%s) failed: %d",
-					kring->name, err);
+			nm_prerr("virtqueue_enqueue(%s) failed: %d",
+				kring->name, err);
 			break;
 		}
 	}
+	rxq->vtnrx_nm_refill = nm_i;
 
-	return nm_i;
+	return num == 0 ? 0 : ENOSPC;
 }
 
 /*
@@ -274,11 +277,14 @@ vtnet_netmap_rxq_populate(struct vtnet_rxq *rxq)
 	/* Expose all the RX netmap buffers we can. In case of no indirect
 	 * buffers, the number of netmap slots in the RX ring matches the
 	 * maximum number of 2-elements sglist that the RX virtqueue can
-	 * accommodate (minus 1 to avoid netmap ring wraparound). */
+	 * accommodate. We need to start from kring->nr_hwcur, which is 0
+	 * on netmap register and may be different from 0 if a virtio
+	 * re-init happens while the device is in use by netmap. */
+	rxq->vtnrx_nm_refill = kring->nr_hwcur;
 	error = vtnet_netmap_kring_refill(kring, na->num_rx_desc - 1);
 	virtqueue_notify(rxq->vtnrx_vq);
 
-	return error < 0 ? ENXIO : 0;
+	return error;
 }
 
 /* Reconcile kernel and user view of the receive ring. */
@@ -350,15 +356,19 @@ vtnet_netmap_rxsync(struct netmap_kring *kring, int fl
 	 */
 	nm_i = kring->nr_hwcur; /* netmap ring index */
 	if (nm_i != head) {
-		int howmany = head - nm_i;
-		int nm_j;
+		int released;
+		int error;
 
-		if (howmany < 0)
-			howmany += kring->nkr_num_slots;
-		nm_j = vtnet_netmap_kring_refill(kring, howmany);
-		if (nm_j < 0)
-			return nm_j;
-		kring->nr_hwcur = nm_j;
+		released = head - nm_i;
+		if (released < 0)
+			released += kring->nkr_num_slots;
+		error = vtnet_netmap_kring_refill(kring, released);
+		if (error) {
+			nm_prerr("Failed to replenish RX VQ with %u sgs",
+			    released);
+			return error;
+		}
+		kring->nr_hwcur = head;
 		virtqueue_notify(vq);
 	}
 

Modified: head/sys/dev/virtio/network/if_vtnetvar.h
==============================================================================
--- head/sys/dev/virtio/network/if_vtnetvar.h	Wed Jun  3 17:26:00 2020	(r361757)
+++ head/sys/dev/virtio/network/if_vtnetvar.h	Wed Jun  3 17:42:17 2020	(r361758)
@@ -80,6 +80,7 @@ struct vtnet_rxq {
 	struct taskqueue	*vtnrx_tq;
 	struct task		 vtnrx_intrtask;
 #ifdef DEV_NETMAP
+	uint32_t		 vtnrx_nm_refill;
 	struct virtio_net_hdr_mrg_rxbuf vtnrx_shrhdr;
 #endif  /* DEV_NETMAP */
 	char			 vtnrx_name[16];