From 54fec33582aa60a76902dbe24ac8c1b5650e8e63 Mon Sep 17 00:00:00 2001 From: Vladimir Oltean Date: Sat, 26 Sep 2020 22:32:08 +0300 Subject: [PATCH] net: flow_dissector: avoid indirect call to DSA .flow_dissect for generic case With the recent mitigations against speculative execution exploits, indirect function calls are more expensive and it would be good to avoid them where possible. In the case of DSA, most switch taggers will shift the EtherType and next headers by a fixed amount equal to that tag's length in bytes. So we can use a generic procedure to determine that, without calling into custom tagger code. However we still leave the flow_dissect method inside struct dsa_device_ops as an override for the generic function. Suggested-by: Andrew Lunn Signed-off-by: Vladimir Oltean Signed-off-by: David S. Miller --- net/core/flow_dissector.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index 13cc4c0a8863..e21950a2c897 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -932,8 +932,14 @@ bool __skb_flow_dissect(const struct net *net, int offset = 0; ops = skb->dev->dsa_ptr->tag_ops; - if (ops->flow_dissect) { - ops->flow_dissect(skb, &proto, &offset); + /* Tail taggers don't break flow dissection */ + if (!ops->tail_tag) { + if (ops->flow_dissect) + ops->flow_dissect(skb, &proto, &offset); + else + dsa_tag_generic_flow_dissect(skb, + &proto, + &offset); hlen -= offset; nhoff += offset; }