netdev - [PATCH RFC bpf-next v2 1/5] netlink: specs: Add XDP RX checksum capability to XDP metadata specs

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Message-Id: <20250925-bpf-xdp-meta-rxcksum-v2-1-6b3fe987ce91@kernel.org>
Date: Thu, 25 Sep 2025 11:30:33 +0200
From: Lorenzo Bianconi <lorenzo@...nel.org>
To: Donald Hunter <donald.hunter@...il.com>, 
 Jakub Kicinski <kuba@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>, 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>, Andrew Lunn <andrew+netdev@...n.ch>, 
 Tony Nguyen <anthony.l.nguyen@...el.com>, 
 Przemek Kitszel <przemyslaw.kitszel@...el.com>, 
 Alexander Lobakin <aleksander.lobakin@...el.com>, 
 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>, 
 Shuah Khan <shuah@...nel.org>, 
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, 
 intel-wired-lan@...ts.osuosl.org, linux-kselftest@...r.kernel.org, 
 Lorenzo Bianconi <lorenzo@...nel.org>
Subject: [PATCH RFC bpf-next v2 1/5] netlink: specs: Add XDP RX checksum
 capability to XDP metadata specs

Introduce XDP RX checksum capability to XDP metadata specs. XDP RX
checksum will be use by devices capable of exposing receive checksum
result via bpf_xdp_metadata_rx_checksum().
Moreover, introduce xmo_rx_checksum netdev callback in order allow the
eBPF program bounded to the device to retrieve the RX checksum result
computed by the hw NIC.

Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
---
 Documentation/netlink/specs/netdev.yaml |  5 +++++
 include/net/xdp.h                       | 14 ++++++++++++++
 net/core/xdp.c                          | 29 +++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
index e00d3fa1c152d7165e9485d6d383a2cc9cef7cfd..00699bf4a7fdb67c6b9ee3548098b0c933fd39a4 100644
--- a/Documentation/netlink/specs/netdev.yaml
+++ b/Documentation/netlink/specs/netdev.yaml
@@ -61,6 +61,11 @@ definitions:
         doc: |
           Device is capable of exposing receive packet VLAN tag via
           bpf_xdp_metadata_rx_vlan_tag().
+      -
+        name: checksum
+        doc: |
+          Device is capable of exposing receive checksum result via
+          bpf_xdp_metadata_rx_checksum().
   -
     type: flags
     name: xsk-flags
diff --git a/include/net/xdp.h b/include/net/xdp.h
index aa742f413c358575396530879af4570dc3fc18de..9ab9ac10ae2074b70618a9d4f32544d8b9a30b63 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -586,6 +586,10 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
 			   NETDEV_XDP_RX_METADATA_VLAN_TAG, \
 			   bpf_xdp_metadata_rx_vlan_tag, \
 			   xmo_rx_vlan_tag) \
+	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_CHECKSUM, \
+			   NETDEV_XDP_RX_METADATA_CHECKSUM, \
+			   bpf_xdp_metadata_rx_checksum, \
+			   xmo_rx_checksum)
 
 enum xdp_rx_metadata {
 #define XDP_METADATA_KFUNC(name, _, __, ___) name,
@@ -643,12 +647,22 @@ enum xdp_rss_hash_type {
 	XDP_RSS_TYPE_L4_IPV6_SCTP_EX = XDP_RSS_TYPE_L4_IPV6_SCTP | XDP_RSS_L3_DYNHDR,
 };
 
+enum xdp_checksum {
+	XDP_CHECKSUM_NONE		= CHECKSUM_NONE,
+	XDP_CHECKSUM_UNNECESSARY	= CHECKSUM_UNNECESSARY,
+	XDP_CHECKSUM_COMPLETE		= CHECKSUM_COMPLETE,
+	XDP_CHECKSUM_PARTIAL		= CHECKSUM_PARTIAL,
+};
+
 struct xdp_metadata_ops {
 	int	(*xmo_rx_timestamp)(const struct xdp_md *ctx, u64 *timestamp);
 	int	(*xmo_rx_hash)(const struct xdp_md *ctx, u32 *hash,
 			       enum xdp_rss_hash_type *rss_type);
 	int	(*xmo_rx_vlan_tag)(const struct xdp_md *ctx, __be16 *vlan_proto,
 				   u16 *vlan_tci);
+	int	(*xmo_rx_checksum)(const struct xdp_md *ctx,
+				   enum xdp_checksum *ip_summed,
+				   u32 *cksum_meta);
 };
 
 #ifdef CONFIG_NET
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 9100e160113a9a1e2cb88e7602e85c5f36a9f3b9..4362a5d294c9117ab69dab00deefbd8fcd62d6cd 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -961,6 +961,35 @@ __bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx,
 	return -EOPNOTSUPP;
 }
 
+/**
+ * bpf_xdp_metadata_rx_checksum - Read XDP frame RX checksum.
+ * @ctx: XDP context pointer.
+ * @ip_summed: Return value pointer indicating checksum result.
+ * @cksum_meta: Return value pointer indicating checksum result metadata.
+ *
+ * In case of success, ``ip_summed`` is set to the RX checksum result. Possible
+ * values are:
+ * ``XDP_CHECKSUM_NONE``
+ * ``XDP_CHECKSUM_UNNECESSARY``
+ * ``XDP_CHECKSUM_COMPLETE``
+ * ``XDP_CHECKSUM_PARTIAL``
+ *
+ * In case of success, ``cksum_meta`` contains the hw computed checksum value
+ * for ``XDP_CHECKSUM_COMPLETE`` or the ``csum_level`` for
+ * ``XDP_CHECKSUM_UNNECESSARY``. It is set to 0 for ``XDP_CHECKSUM_NONE`` and
+ * ``XDP_CHECKSUM_PARTIAL``.
+ *
+ * Return:
+ * * Returns 0 on success or ``-errno`` on error.
+ * * ``-EOPNOTSUPP`` : means device driver does not implement kfunc
+ * * ``-ENODATA``    : means no RX-timestamp available for this frame
+ */
+__bpf_kfunc int bpf_xdp_metadata_rx_checksum(const struct xdp_md *ctx,
+					     u8 *ip_summed, u32 *cksum_meta)
+{
+	return -EOPNOTSUPP;
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(xdp_metadata_kfunc_ids)

-- 
2.51.0