Subject: [PATCH 4/7] net: openvswitch: Reduce push_nsh stack usage

From: Nicholas Piggin <[email-masked]>
Date: Wed, 11 Oct 2023 13:43:41 +1000

Use percpu data to move the large temporary buffer off the push_nsh
stack. This reduces stack consumption from 336 bytes to 64 bytes.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 net/openvswitch/actions.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index be15ef693284..fa53e22f3ebe 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -349,12 +349,18 @@ static int push_eth(struct sk_buff *skb, struct sw_flow_key *key,
 	return 0;
 }
 
+struct tmp_nsh_hdr {
+	u8 data[NSH_HDR_MAX_LEN];
+};
+
+static DEFINE_PER_CPU(struct tmp_nsh_hdr, tmp_nsh_hdr);
+
 static noinline_for_stack int push_nsh(struct sk_buff *skb,
 				       struct sw_flow_key *key,
 				       const struct nlattr *a)
 {
-	u8 buffer[NSH_HDR_MAX_LEN];
-	struct nshhdr *nh = (struct nshhdr *)buffer;
+	struct tmp_nsh_hdr *hdr = this_cpu_ptr(&tmp_nsh_hdr);
+	struct nshhdr *nh = (struct nshhdr *)&hdr->data[0];
 	int err;
 
 	err = nsh_hdr_from_nlattr(a, nh, NSH_HDR_MAX_LEN);
-- 
2.42.0