[RFC PATCH bpf-next v1 3/7] xdp: add bpf_xdp_metadata_rx_csum() RX metadata kfunc
From: Vladimir Vdovin <hidden>
Date: 2026-06-30 19:18:02
Also in:
bpf
Subsystem:
networking drivers, networking [general], the rest, xdp (express data path), yaml netlink (ynl) · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Alexei Starovoitov, Daniel Borkmann, David S. Miller, Jesper Dangaard Brouer, John Fastabend, Donald Hunter
Add a device-bound RX-metadata kfunc that reports the hardware checksum verdict (enum xdp_csum_status: XDP_CSUM_NONE / XDP_CSUM_VERIFIED) through a new xmo_rx_csum operation, so an XDP program can make an informed decision (e.g. call bpf_xdp_assert_rx_csum()) instead of trusting blindly. Wire it into the XDP_METADATA_KFUNC machinery and advertise it via NETDEV_XDP_RX_METADATA_CSUM. Signed-off-by: Vladimir Vdovin <redacted> --- Documentation/netlink/specs/netdev.yaml | 5 +++++ include/net/xdp.h | 12 ++++++++++++ include/uapi/linux/netdev.h | 3 +++ net/core/xdp.c | 23 +++++++++++++++++++++++ tools/include/uapi/linux/netdev.h | 3 +++ 5 files changed, 46 insertions(+)
diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
index 5f143da7458c..86017f7402d9 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: csum + doc: | + Device is capable of exposing receive packet checksum status via + bpf_xdp_metadata_rx_csum(). - type: flags name: xsk-flags
diff --git a/include/net/xdp.h b/include/net/xdp.h
index 5a1e2cc9c312..40f6fba41962 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h@@ -597,6 +597,10 @@ 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_CSUM, \ + NETDEV_XDP_RX_METADATA_CSUM, \ + bpf_xdp_metadata_rx_csum, \ + xmo_rx_csum) \ enum xdp_rx_metadata { #define XDP_METADATA_KFUNC(name, _, __, ___) name,
@@ -654,12 +658,20 @@ enum xdp_rss_hash_type { XDP_RSS_TYPE_L4_IPV6_SCTP_EX = XDP_RSS_TYPE_L4_IPV6_SCTP | XDP_RSS_L3_DYNHDR, }; +/* Checksum status reported by bpf_xdp_metadata_rx_csum(). */ +enum xdp_csum_status { + XDP_CSUM_NONE = 0, /* HW did not validate the checksum */ + XDP_CSUM_VERIFIED, /* HW validated the L4 checksum; it is correct */ +}; + 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_csum)(const struct xdp_md *ctx, + enum xdp_csum_status *csum_status); }; #ifdef CONFIG_NET
diff --git a/include/uapi/linux/netdev.h b/include/uapi/linux/netdev.h
index 2f3ab75e8cc0..99cda716f0ee 100644
--- a/include/uapi/linux/netdev.h
+++ b/include/uapi/linux/netdev.h@@ -47,11 +47,14 @@ enum netdev_xdp_act { * hash via bpf_xdp_metadata_rx_hash(). * @NETDEV_XDP_RX_METADATA_VLAN_TAG: Device is capable of exposing receive * packet VLAN tag via bpf_xdp_metadata_rx_vlan_tag(). + * @NETDEV_XDP_RX_METADATA_CSUM: Device is capable of exposing receive packet + * checksum status via bpf_xdp_metadata_rx_csum(). */ enum netdev_xdp_rx_metadata { NETDEV_XDP_RX_METADATA_TIMESTAMP = 1, NETDEV_XDP_RX_METADATA_HASH = 2, NETDEV_XDP_RX_METADATA_VLAN_TAG = 4, + NETDEV_XDP_RX_METADATA_CSUM = 8, }; /**
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 63ee36ec93de..7f4b5c6f7c87 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c@@ -964,6 +964,29 @@ __bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx, return -EOPNOTSUPP; } +/** + * bpf_xdp_metadata_rx_csum - Read the device's RX checksum verdict. + * @ctx: XDP context pointer. + * @csum_status: Destination pointer for the checksum status. + * + * Report what the hardware concluded about the packet's checksum, so the + * program can decide whether to assert it (e.g. via bpf_xdp_assert_rx_csum() + * before a cpumap redirect) instead of having the stack validate it again. + * + * On ``XDP_CSUM_VERIFIED`` the device has checked the L4 checksum and it is + * correct. ``XDP_CSUM_NONE`` means the device did not validate it. + * + * Return: + * * Returns 0 on success or ``-errno`` on error. + * * ``-EOPNOTSUPP`` : device driver doesn't implement kfunc + * * ``-ENODATA`` : checksum information is not available + */ +__bpf_kfunc int bpf_xdp_metadata_rx_csum(const struct xdp_md *ctx, + enum xdp_csum_status *csum_status) +{ + return -EOPNOTSUPP; +} + /** * bpf_xdp_assert_rx_csum - Assert the packet's L4 checksum is correct. * @ctx: XDP context pointer.
diff --git a/tools/include/uapi/linux/netdev.h b/tools/include/uapi/linux/netdev.h
index 2f3ab75e8cc0..99cda716f0ee 100644
--- a/tools/include/uapi/linux/netdev.h
+++ b/tools/include/uapi/linux/netdev.h@@ -47,11 +47,14 @@ enum netdev_xdp_act { * hash via bpf_xdp_metadata_rx_hash(). * @NETDEV_XDP_RX_METADATA_VLAN_TAG: Device is capable of exposing receive * packet VLAN tag via bpf_xdp_metadata_rx_vlan_tag(). + * @NETDEV_XDP_RX_METADATA_CSUM: Device is capable of exposing receive packet + * checksum status via bpf_xdp_metadata_rx_csum(). */ enum netdev_xdp_rx_metadata { NETDEV_XDP_RX_METADATA_TIMESTAMP = 1, NETDEV_XDP_RX_METADATA_HASH = 2, NETDEV_XDP_RX_METADATA_VLAN_TAG = 4, + NETDEV_XDP_RX_METADATA_CSUM = 8, }; /**
--
2.47.0