netdev - [PATCH bpf-next v8 09/12] bpf: support SCM_TSTAMP_ACK of SO

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Message-Id: <20250204183024.87508-10-kerneljasonxing@gmail.com>
Date: Wed,  5 Feb 2025 02:30:21 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	dsahern@...nel.org,
	willemdebruijn.kernel@...il.com,
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Cc: bpf@...r.kernel.org,
	netdev@...r.kernel.org,
	Jason Xing <kerneljasonxing@...il.com>
Subject: [PATCH bpf-next v8 09/12] bpf: support SCM_TSTAMP_ACK of SO_TIMESTAMPING

Handle the ACK timestamp case. Actually testing SKBTX_BPF flag
can work, but Introducing a new txstamp_ack_bpf to avoid cache
line misses in tcp_ack_tstamp() is needed. To be more specific,
in most cases, normal flows would not access skb_shinfo as
txstamp_ack is zero, so that this function won't appear in the
hot spot lists. Introducing a new member txstamp_ack_bpf works
similarly.

Signed-off-by: Jason Xing <kerneljasonxing@...il.com>
---
 include/net/tcp.h              | 3 ++-
 include/uapi/linux/bpf.h       | 5 +++++
 net/core/skbuff.c              | 3 +++
 net/ipv4/tcp_input.c           | 3 ++-
 net/ipv4/tcp_output.c          | 5 +++++
 tools/include/uapi/linux/bpf.h | 5 +++++
 6 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 293047694710..88429e422301 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -959,9 +959,10 @@ struct tcp_skb_cb {
 	__u8		sacked;		/* State flags for SACK.	*/
 	__u8		ip_dsfield;	/* IPv4 tos or IPv6 dsfield	*/
 	__u8		txstamp_ack:1,	/* Record TX timestamp for ack? */
+			txstamp_ack_bpf:1,	/* ack timestamp for bpf use */
 			eor:1,		/* Is skb MSG_EOR marked? */
 			has_rxtstamp:1,	/* SKB has a RX timestamp	*/
-			unused:5;
+			unused:4;
 	__u32		ack_seq;	/* Sequence number ACK'd	*/
 	union {
 		struct {
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 4c3566f623c2..800122a8abe5 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7047,6 +7047,11 @@ enum {
 					 * timestamp that hardware just
 					 * generates.
 					 */
+	BPF_SOCK_OPS_TS_ACK_OPT_CB,	/* Called when all the skbs in the
+					 * same sendmsg call are acked
+					 * when SK_BPF_CB_TX_TIMESTAMPING
+					 * feature is on.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 264435f989ad..a8463fef574a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5579,6 +5579,9 @@ static void skb_tstamp_tx_bpf(struct sk_buff *skb, struct sock *sk,
 		if (!sw && hwtstamps)
 			*skb_hwtstamps(skb) = *hwtstamps;
 		break;
+	case SCM_TSTAMP_ACK:
+		op = BPF_SOCK_OPS_TS_ACK_OPT_CB;
+		break;
 	default:
 		return;
 	}
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 62252702929d..c8945f5be31b 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3323,7 +3323,8 @@ static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
 	const struct skb_shared_info *shinfo;
 
 	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
-	if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
+	if (likely(!TCP_SKB_CB(skb)->txstamp_ack &&
+		   !TCP_SKB_CB(skb)->txstamp_ack_bpf))
 		return;
 
 	shinfo = skb_shinfo(skb);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 695749807c09..fc84ca669b76 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1556,6 +1556,7 @@ static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int de
 static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
 {
 	return TCP_SKB_CB(skb)->txstamp_ack ||
+	       TCP_SKB_CB(skb)->txstamp_ack_bpf ||
 		(skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
 }
 
@@ -1572,7 +1573,9 @@ static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
 		shinfo2->tx_flags |= tsflags;
 		swap(shinfo->tskey, shinfo2->tskey);
 		TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
+		TCP_SKB_CB(skb2)->txstamp_ack_bpf = TCP_SKB_CB(skb)->txstamp_ack_bpf;
 		TCP_SKB_CB(skb)->txstamp_ack = 0;
+		TCP_SKB_CB(skb)->txstamp_ack_bpf = 0;
 	}
 }
 
@@ -3213,6 +3216,8 @@ void tcp_skb_collapse_tstamp(struct sk_buff *skb,
 		shinfo->tskey = next_shinfo->tskey;
 		TCP_SKB_CB(skb)->txstamp_ack |=
 			TCP_SKB_CB(next_skb)->txstamp_ack;
+		TCP_SKB_CB(skb)->txstamp_ack_bpf |=
+			TCP_SKB_CB(next_skb)->txstamp_ack_bpf;
 	}
 }
 
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 974b7f61d11f..06e68d772989 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7040,6 +7040,11 @@ enum {
 					 * timestamp that hardware just
 					 * generates.
 					 */
+	BPF_SOCK_OPS_TS_ACK_OPT_CB,	/* Called when all the skbs in the
+					 * same sendmsg call are acked
+					 * when SK_BPF_CB_TX_TIMESTAMPING
+					 * feature is on.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
-- 
2.43.5