svn commit: r361698 - head/sys/dev/netmap

[Vincenzo Maffione]

Author: vmaffione
Date: Mon Jun  1 16:14:29 2020
New Revision: 361698
URL: https://svnweb.freebsd.org/changeset/base/361698

Log:
  netmap: if_vtnet: avoid netmap ring wraparound
  
  netmap assumes the one "slot" is left unused to distinguish
  the empty ring and full ring conditions. This assumption was
  violated by vtnet_netmap_rxq_populate().
  
  MFC after:	1 week

Modified:
  head/sys/dev/netmap/if_vtnet_netmap.h

Modified: head/sys/dev/netmap/if_vtnet_netmap.h
==============================================================================
--- head/sys/dev/netmap/if_vtnet_netmap.h	Mon Jun  1 16:12:09 2020	(r361697)
+++ head/sys/dev/netmap/if_vtnet_netmap.h	Mon Jun  1 16:14:29 2020	(r361698)
@@ -275,8 +275,8 @@ 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. */
-	error = vtnet_netmap_kring_refill(kring, na->num_rx_desc);
+	 * accommodate (minus 1 to avoid netmap ring wraparound). */
+	error = vtnet_netmap_kring_refill(kring, na->num_rx_desc - 1);
 	virtqueue_notify(rxq->vtnrx_vq);
 
 	return error < 0 ? ENXIO : 0;