netdev - [PATCH net 4/4] bpf, cpumap: Flush xdp after cpu_map_bpf_prog_run

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Date: Fri,  8 Sep 2023 15:57:48 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: netdev@...r.kernel.org,
	bpf@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Andrii Nakryiko <andrii@...nel.org>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	KP Singh <kpsingh@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Yonghong Song <yonghong.song@...ux.dev>
Subject: [PATCH net 4/4] bpf, cpumap: Flush xdp after cpu_map_bpf_prog_run_skb().

xdp_do_flush() should be invoked before leaving the NAPI poll function
if XDP-redirect has been performed.

There are two possible XDP invocations in cpu_map_bpf_prog_run():
- cpu_map_bpf_prog_run_xdp()
- cpu_map_bpf_prog_run_skb()

Both functions update stats->redirect if a redirect is performed but
xdp_do_flush() is only invoked after the former.

Invoke xdp_do_flush() after both functions run and a redirect was
performed.

Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Hao Luo <haoluo@...gle.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: KP Singh <kpsingh@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: Song Liu <song@...nel.org>
Cc: Stanislav Fomichev <sdf@...gle.com>
Cc: Yonghong Song <yonghong.song@...ux.dev>
Fixes: 11941f8a85362 ("bpf: cpumap: Implement generic cpumap")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 kernel/bpf/cpumap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index e42a1bdb7f536..f3ba11b4a732b 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -248,12 +248,12 @@ static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
 
 	nframes = cpu_map_bpf_prog_run_xdp(rcpu, frames, xdp_n, stats);
 
-	if (stats->redirect)
-		xdp_do_flush();
-
 	if (unlikely(!list_empty(list)))
 		cpu_map_bpf_prog_run_skb(rcpu, list, stats);
 
+	if (stats->redirect)
+		xdp_do_flush();
+
 	rcu_read_unlock_bh(); /* resched point, may call do_softirq() */
 
 	return nframes;
-- 
2.40.1