linux-kernel - [PATCH bpf-next,v2 2/2] selftests/bpf: Enhance XDP Rx Metadata Handling

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Message-Id: <20250702030349.3275368-3-yoong.siang.song@intel.com>
Date: Wed,  2 Jul 2025 11:03:49 +0800
From: Song Yoong Siang <yoong.siang.song@...el.com>
To: "David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Mykola Lysenko <mykolal@...com>,
	Shuah Khan <shuah@...nel.org>
Cc: netdev@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next,v2 2/2] selftests/bpf: Enhance XDP Rx Metadata Handling

Introduce the XDP_METADATA_SIZE macro to ensure that user applications can
consistently retrieve the correct location of struct xdp_meta.

Prior to this commit, the XDP program adjusted the data_meta backward by
the size of struct xdp_meta, while the user application retrieved the data
by calculating backward from the data pointer. This approach only worked if
xdp_buff->data_meta was equal to xdp_buff->data before calling
bpf_xdp_adjust_meta.

With the introduction of XDP_METADATA_SIZE, both the XDP program and user
application now calculate and identify the location of struct xdp_meta from
the data pointer. This ensures the implementation remains functional even
when there is device-reserved metadata, making the tests more portable
across different NICs.

Signed-off-by: Song Yoong Siang <yoong.siang.song@...el.com>
---
 tools/testing/selftests/bpf/prog_tests/xdp_metadata.c | 2 +-
 tools/testing/selftests/bpf/progs/xdp_hw_metadata.c   | 2 +-
 tools/testing/selftests/bpf/progs/xdp_metadata.c      | 2 +-
 tools/testing/selftests/bpf/xdp_hw_metadata.c         | 2 +-
 tools/testing/selftests/bpf/xdp_metadata.h            | 7 +++++++
 5 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
index 19f92affc2da..8d6c2633698b 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
@@ -302,7 +302,7 @@ static int verify_xsk_metadata(struct xsk *xsk, bool sent_from_af_xdp)
 
 	/* custom metadata */
 
-	meta = data - sizeof(struct xdp_meta);
+	meta = data - XDP_METADATA_SIZE;
 
 	if (!ASSERT_NEQ(meta->rx_timestamp, 0, "rx_timestamp"))
 		return -1;
diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
index 330ece2eabdb..3766f58d3486 100644
--- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
+++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c
@@ -72,7 +72,7 @@ int rx(struct xdp_md *ctx)
 		return XDP_PASS;
 	}
 
-	err = bpf_xdp_adjust_meta(ctx, -(int)sizeof(struct xdp_meta));
+	err = bpf_xdp_adjust_meta(ctx, -(int)XDP_METADATA_SIZE);
 	if (err) {
 		__sync_add_and_fetch(&pkts_fail, 1);
 		return XDP_PASS;
diff --git a/tools/testing/selftests/bpf/progs/xdp_metadata.c b/tools/testing/selftests/bpf/progs/xdp_metadata.c
index 09bb8a038d52..5cada85fe0f4 100644
--- a/tools/testing/selftests/bpf/progs/xdp_metadata.c
+++ b/tools/testing/selftests/bpf/progs/xdp_metadata.c
@@ -73,7 +73,7 @@ int rx(struct xdp_md *ctx)
 
 	/* Reserve enough for all custom metadata. */
 
-	ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(struct xdp_meta));
+	ret = bpf_xdp_adjust_meta(ctx, -(int)XDP_METADATA_SIZE);
 	if (ret != 0)
 		return XDP_DROP;
 
diff --git a/tools/testing/selftests/bpf/xdp_hw_metadata.c b/tools/testing/selftests/bpf/xdp_hw_metadata.c
index 3d8de0d4c96a..a529d55d4ff4 100644
--- a/tools/testing/selftests/bpf/xdp_hw_metadata.c
+++ b/tools/testing/selftests/bpf/xdp_hw_metadata.c
@@ -223,7 +223,7 @@ static void verify_xdp_metadata(void *data, clockid_t clock_id)
 {
 	struct xdp_meta *meta;
 
-	meta = data - sizeof(*meta);
+	meta = data - XDP_METADATA_SIZE;
 
 	if (meta->hint_valid & XDP_META_FIELD_RSS)
 		printf("rx_hash: 0x%X with RSS type:0x%X\n",
diff --git a/tools/testing/selftests/bpf/xdp_metadata.h b/tools/testing/selftests/bpf/xdp_metadata.h
index 87318ad1117a..2dfd3bf5e7bb 100644
--- a/tools/testing/selftests/bpf/xdp_metadata.h
+++ b/tools/testing/selftests/bpf/xdp_metadata.h
@@ -50,3 +50,10 @@ struct xdp_meta {
 	};
 	enum xdp_meta_field hint_valid;
 };
+
+/* XDP_METADATA_SIZE must be at least the size of struct xdp_meta. An additional
+ * 32 bytes of padding is included as a conservative measure to accommodate any
+ * metadata areas reserved by Ethernet devices. If the device-reserved metadata
+ * exceeds 32 bytes, this value will need adjustment.
+ */
+#define XDP_METADATA_SIZE	(sizeof(struct xdp_meta) + 32)
-- 
2.34.1