[PATCH 3.2 179/199] netvsc: reduce maximum GSO size

[Ben Hutchings]

3.2.87-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: stephen hemminger <step...@networkplumber.org>

[ Upstream commit a50af86dd49ee1851d1ccf06dd0019c05b95e297 ]

Hyper-V (and Azure) support using NVGRE which requires some extra space
for encapsulation headers. Because of this the largest allowed TSO
packet is reduced.

For older releases, hard code a fixed reduced value.  For next release,
there is a better solution which uses result of host offload
negotiation.

Signed-off-by: Stephen Hemminger <sthem...@microsoft.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 drivers/staging/hv/netvsc_drv.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/staging/hv/netvsc_drv.c
+++ b/drivers/staging/hv/netvsc_drv.c
@@ -52,6 +52,9 @@ struct net_device_context {
 /* Need this many pages to handle worst case fragmented packet */
 #define PACKET_PAGES_HIWATER  (MAX_SKB_FRAGS + 2)
 
+/* Restrict GSO size to account for NVGRE */
+#define NETVSC_GSO_MAX_SIZE    62768
+
 static int ring_size = 128;
 module_param(ring_size, int, S_IRUGO);
 MODULE_PARM_DESC(ring_size, "Ring buffer size (# of pages)");
@@ -363,6 +366,7 @@ static int netvsc_probe(struct hv_device
 
        SET_ETHTOOL_OPS(net, &ethtool_ops);
        SET_NETDEV_DEV(net, &dev->device);
+       netif_set_gso_max_size(net, NETVSC_GSO_MAX_SIZE);
 
        ret = register_netdev(net);
        if (ret != 0) {