Subject: [RFC PATCH 1/7] net: openvswitch: Move NSH buffer out of do_execute_actions

From: Nicholas Piggin <[email-masked]>
Date: Wed, 27 Sep 2023 10:13:02 +1000

This takes do_execute_actions stack use from 544 bytes to 288
bytes. execute_push_nsh uses 336 bytes, but it is a leaf call not
involved in recursion.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 net/openvswitch/actions.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index fd66014d8a76..8933caa92794 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -1286,6 +1286,21 @@ static int execute_dec_ttl(struct sk_buff *skb, struct sw_flow_key *key)
 	return 0;
 }
 
+static noinline_for_stack int execute_push_nsh(struct sk_buff *skb,
+					       struct sw_flow_key *key,
+					       const struct nlattr *attr)
+{
+	u8 buffer[NSH_HDR_MAX_LEN];
+	struct nshhdr *nh = (struct nshhdr *)buffer;
+	int err;
+
+	err = nsh_hdr_from_nlattr(attr, nh, NSH_HDR_MAX_LEN);
+	if (likely(!err))
+		err = push_nsh(skb, key, nh);
+
+	return err;
+}
+
 /* Execute a list of actions against 'skb'. */
 static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 			      struct sw_flow_key *key,
@@ -1439,17 +1454,9 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
 			err = pop_eth(skb, key);
 			break;
 
-		case OVS_ACTION_ATTR_PUSH_NSH: {
-			u8 buffer[NSH_HDR_MAX_LEN];
-			struct nshhdr *nh = (struct nshhdr *)buffer;
-
-			err = nsh_hdr_from_nlattr(nla_data(a), nh,
-						  NSH_HDR_MAX_LEN);
-			if (unlikely(err))
-				break;
-			err = push_nsh(skb, key, nh);
+		case OVS_ACTION_ATTR_PUSH_NSH:
+			err = execute_push_nsh(skb, key, nla_data(a));
 			break;
-		}
 
 		case OVS_ACTION_ATTR_POP_NSH:
 			err = pop_nsh(skb, key);
-- 
2.40.1