Introduce bpf_xdp_metadata_rx_checksum() kfunc in order to load the HW
RX checksum results in the eBPF program bound to the NIC.
Implement xmo_rx_checksum callback for veth and ice drivers.

If the hardware detects a wrong/failed checksum, it will report
CHECKSUM_NONE in the packet metadata. Moreover, CHECKSUM_NONE will be
returned even if the NIC can't parse the packet (e.g. if it does not
support a specific protocol). A possible use case for
bpf_xdp_metadata_rx_checksum() would be to implement a XDP DDoS
application [1] combining the info from bpf_xdp_metadata_rx_checksum()
and bpf_xdp_metadata_rx_hash() kfuncs in order to filter packets with a
wrong/failed checksum.

This is a repost of Lorenzo's series, rebased on top of net-next, with
a new drv-net selftest for the RX checksum metadata added on top of it,
as Lorenzo suggested [2].

A note on the new selftest semantics: for traffic with a correct
checksum the test requires a usable verdict (CHECKSUM_UNNECESSARY
and/or CHECKSUM_COMPLETE) but reports SKIP on CHECKSUM_NONE, since the
API allows devices that do not verify the packets (e.g. veth reports
NONE for locally generated CHECKSUM_PARTIAL traffic). For corrupted
packets it only asserts that CHECKSUM_UNNECESSARY is not set, as
CHECKSUM_COMPLETE legitimately carries the raw checksum of bad packets
too.

[1] https://blog.cloudflare.com/unimog-cloudflares-edge-load-balancer/
[2] https://lore.kernel.org/r/ak5ox296M46FAcWX@lore-desk (local)

---
Changes in v4:
- Report ip_summed as a bitmask of XDP_CHECKSUM_* values and return the
  hw checksum and the checksum level via dedicated
  bpf_xdp_metadata_rx_checksum() arguments
- Rebase on top of net-next
- Add a drv-net selftest for the XDP RX checksum metadata
- Link to v3: https://lore.kernel.org/r/20260217-bpf-xdp-meta-rxcksum-v3-0-30024c50ba71@kernel.org (local)

Changes in v3:
- Remove leftover assignment from v2 in veth_xdp_rx_checksum()
- Fix typos
- Fix commit logs
- Link to v2: https://lore.kernel.org/r/20260213-bpf-xdp-meta-rxcksum-v2-0-a82c4802afbe@kernel.org (local)

Changes in v2:
- Remove XDP_CHECKSUM_PARTIAL definition
- Improve veth_xdp_rx_checksum() callback
- Fix uninitialized case for cksum_meta in ice_get_rx_csum()
- Fix sparse warnings in ice driver
- Fix typos
- Link to v1: https://lore.kernel.org/r/20260210-bpf-xdp-meta-rxcksum-v1-0-e5d55caa0541@kernel.org (local)

Changes in v1:
- Rebase on top of bpf-next
- Test ice driver using xdp_hw_metadata tool available in the bpf
  kernel selftest
- Improve cover letter with an use-case for
  bpf_xdp_metadata_rx_checksum()
- Link to RFC v2: https://lore.kernel.org/r/20250925-bpf-xdp-meta-rxcksum-v2-0-6b3fe987ce91@kernel.org (local)

change-id: 20250925-bpf-xdp-meta-rxcksum-900685e2909d

Lorenzo Bianconi (5):
  netlink: specs: Add XDP RX checksum capability to XDP metadata specs
  net: veth: Add xmo_rx_checksum callback to veth driver
  net: ice: Add xmo_rx_checksum callback
  selftests/bpf: Add selftest support for bpf_xdp_metadata_rx_checksum
  selftests/bpf: Add bpf_xdp_metadata_rx_checksum support to
    xdp_hw_metadat prog

Vladimir Vdovin (1):
  selftests: drv-net: add XDP RX checksum metadata tests

 Documentation/netlink/specs/netdev.yaml       |   5 +
 drivers/net/ethernet/intel/ice/ice_txrx_lib.c | 123 ++++++++++++------
 drivers/net/veth.c                            |  32 +++++
 include/net/xdp.h                             |  18 +++
 include/uapi/linux/netdev.h                   |   3 +
 net/core/xdp.c                                |  32 +++++
 tools/include/uapi/linux/netdev.h             |   3 +
 .../selftests/bpf/prog_tests/xdp_metadata.c   |   9 ++
 .../selftests/bpf/progs/xdp_hw_metadata.c     |   7 +
 .../selftests/bpf/progs/xdp_metadata.c        |   2 +
 tools/testing/selftests/bpf/xdp_hw_metadata.c |  31 +++++
 tools/testing/selftests/bpf/xdp_metadata.h    |  13 ++
 .../selftests/drivers/net/hw/xdp_metadata.py  | 110 ++++++++++++++++
 .../selftests/net/lib/xdp_metadata.bpf.c      | 112 ++++++++++++++--
 14 files changed, 445 insertions(+), 55 deletions(-)


base-commit: 08030ddb87b4c6c6a2c03c82731b5e188f02f5b9
-- 
2.47.0