linux-kernel - [PATCH 4.19 073/346] vxlan: Add needed

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Date:   Mon, 28 Dec 2020 13:46:32 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Annika Wickert <annika.wickert@...ring.de>,
        Sven Eckelmann <sven@...fation.org>,
        Annika Wickert <aw@...nx.space>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 073/346] vxlan: Add needed_headroom for lower device

From: Sven Eckelmann <sven@...fation.org>

[ Upstream commit 0a35dc41fea67ac4495ce7584406bf9557a6e7d0 ]

It was observed that sending data via batadv over vxlan (on top of
wireguard) reduced the performance massively compared to raw ethernet or
batadv on raw ethernet. A check of perf data showed that the
vxlan_build_skb was calling all the time pskb_expand_head to allocate
enough headroom for:

  min_headroom = LL_RESERVED_SPACE(dst->dev) + dst->header_len
  		+ VXLAN_HLEN + iphdr_len;

But the vxlan_config_apply only requested needed headroom for:

  lowerdev->hard_header_len + VXLAN6_HEADROOM or VXLAN_HEADROOM

So it completely ignored the needed_headroom of the lower device. The first
caller of net_dev_xmit could therefore never make sure that enough headroom
was allocated for the rest of the transmit path.

Cc: Annika Wickert <annika.wickert@...ring.de>
Signed-off-by: Sven Eckelmann <sven@...fation.org>
Tested-by: Annika Wickert <aw@...nx.space>
Link: https://lore.kernel.org/r/20201126125247.1047977-1-sven@narfation.org
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/vxlan.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index abf85f0ab72fc..8481a21fe7afb 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -3180,6 +3180,7 @@ static void vxlan_config_apply(struct net_device *dev,
 		dev->gso_max_segs = lowerdev->gso_max_segs;
 
 		needed_headroom = lowerdev->hard_header_len;
+		needed_headroom += lowerdev->needed_headroom;
 
 		max_mtu = lowerdev->mtu - (use_ipv6 ? VXLAN6_HEADROOM :
 					   VXLAN_HEADROOM);
-- 
2.27.0