From: Xin Long <lucien.xin@gmail.com>
Date: Mon, 18 Dec 2017 14:20:56 +0800
Subject: vxlan: update skb dst pmtu on tx path
Patch-mainline: v4.15-rc5
Git-commit: a93bf0ff449064e6b7f44e58522e940f88c0d966
References: bsc#1123456

Unlike ip tunnels, now vxlan doesn't do any pmtu update for
upper dst pmtu, even if it doesn't match the lower dst pmtu
any more.

The problem can be reproduced when reducing the vxlan lower
dev's pmtu when running netperf. In jianlin's testing, the
performance went to 1/7 of the previous.

This patch is to update the upper dst pmtu to match the lower
dst pmtu on tx path so that packets can be sent out even when
lower dev's pmtu has been changed.

It also works for metadata dst.

Note that this patch doesn't process any pmtu icmp packet.
But even in the future, the support for pmtu icmp packets
process of udp tunnels will also needs this.

The same thing will be done for geneve in another patch.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 drivers/net/vxlan.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2181,6 +2181,13 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
 		}
 
 		ndst = &rt->dst;
+		if (skb_dst(skb)) {
+			int mtu = dst_mtu(ndst) - VXLAN_HEADROOM;
+
+			skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL,
+						       skb, mtu);
+		}
+
 		tos = ip_tunnel_ecn_encap(tos, old_iph, skb);
 		ttl = ttl ? : ip4_dst_hoplimit(&rt->dst);
 		err = vxlan_build_skb(skb, ndst, sizeof(struct iphdr),
@@ -2217,6 +2224,13 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
 				goto out_unlock;
 		}
 
+		if (skb_dst(skb)) {
+			int mtu = dst_mtu(ndst) - VXLAN6_HEADROOM;
+
+			skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL,
+						       skb, mtu);
+		}
+
 		tos = ip_tunnel_ecn_encap(tos, old_iph, skb);
 		ttl = ttl ? : ip6_dst_hoplimit(ndst);
 		skb_scrub_packet(skb, xnet);