netvsc: reduce maximum GSO size

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 <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index f6382150b16a..c9140c3aeb67 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -47,6 +47,10 @@
                                  NETIF_F_TSO | \
                                  NETIF_F_TSO6 | \
                                  NETIF_F_HW_CSUM)
+
+/* 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)");
@@ -1400,6 +1404,7 @@ static int netvsc_probe(struct hv_device *dev,
         nvdev = net_device_ctx->nvdev;
         netif_set_real_num_tx_queues(net, nvdev->num_chn);
         netif_set_real_num_rx_queues(net, nvdev->num_chn);
+        netif_set_gso_max_size(net, NETVSC_GSO_MAX_SIZE);
 
         ret = register_netdev(net);
         if (ret != 0) {