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xdp: Allow BPF to set RX hints for XDP_REDIRECTed packets #9245

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Pull request for series with
subject: xdp: Allow BPF to set RX hints for XDP_REDIRECTed packets
version: 2
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=978263

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Upstream branch: 621af19
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=978263
version: 2

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Upstream branch: 564606f
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=978263
version: 2

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Upstream branch: 38d95be
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=978263
version: 2

LorenzoBianconi and others added 6 commits July 2, 2025 14:15
Introduce the `xdp_rx_meta` structure to serve as a container for XDP RX
hardware hints within XDP packet buffers. Initially, this structure will
accommodate `rx_hash` and `rx_vlan` metadata. (The `rx_timestamp` hint will
get stored in `skb_shared_info`).

A key design aspect is making this metadata accessible both during BPF
program execution (via `struct xdp_buff`) and later if an `struct
xdp_frame` is materialized (e.g., for XDP_REDIRECT).
To achieve this:
  - The `struct xdp_frame` embeds an `xdp_rx_meta` field directly for
    storage.
  - The `struct xdp_buff` includes an `xdp_rx_meta` pointer. This pointer
    is initialized (in `xdp_prepare_buff`) to point to the memory location
    within the packet buffer's headroom where the `xdp_frame`'s embedded
    `rx_meta` field would reside.

This setup allows BPF kfuncs, operating on `xdp_buff`, to populate the
metadata in the precise location where it will be found if an `xdp_frame`
is subsequently created.

The availability of this metadata storage area within the buffer is
indicated by the `XDP_FLAGS_META_AREA` flag in `xdp_buff->flags` (and
propagated to `xdp_frame->flags`). This flag is only set if sufficient
headroom (at least `XDP_MIN_HEADROOM`, currently 192 bytes) is present.
Specific hints like `XDP_FLAGS_META_RX_HASH` and `XDP_FLAGS_META_RX_VLAN`
will then denote which types of metadata have been populated into the
`xdp_rx_meta` structure.

This patch is a step for enabling the preservation and use of XDP RX
hints across operations like XDP_REDIRECT.

Signed-off-by: Lorenzo Bianconi <[email protected]>
Signed-off-by: Jesper Dangaard Brouer <[email protected]>
Patchset increased xdp_buff with a pointer 8 bytes, and the bpf/test_run
struct xdp_page_head have two xdp_buff's.  Thus adjust test with 16 bytes.

Signed-off-by: Jesper Dangaard Brouer <[email protected]>
Introduce the following kfuncs to store hw metadata provided by the NIC
into the xdp_buff struct:

- rx-hash: bpf_xdp_store_rx_hash
- rx-vlan: bpf_xdp_store_rx_vlan
- rx-hw-ts: bpf_xdp_store_rx_ts

Signed-off-by: Lorenzo Bianconi <[email protected]>
Signed-off-by: Jesper Dangaard Brouer <[email protected]>
Update the following hw metadata provided by the NIC building the skb
from a xdp_frame.
- rx hash
- rx vlan
- rx hw-ts

Signed-off-by: Lorenzo Bianconi <[email protected]>
Report xdp_rx_meta info if available in xdp_buff struct in
xdp_metadata_ops callbacks for veth driver

Signed-off-by: Lorenzo Bianconi <[email protected]>
Introduce bpf selftests for the XDP rx_meta store kfuncs.

Signed-off-by: Lorenzo Bianconi <[email protected]>
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Upstream branch: 38d95be
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=978263
version: 2

Update the documentation[1] based on the changes in this patchset.

[1] https://docs.kernel.org/networking/xdp-rx-metadata.html

Signed-off-by: Jesper Dangaard Brouer <[email protected]>
@kernel-patches-daemon-bpf kernel-patches-daemon-bpf bot force-pushed the series/978263=>bpf-next branch from ca4dc27 to e8e6878 Compare July 2, 2025 21:15
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=978263 expired. Closing PR.

@kernel-patches-daemon-bpf kernel-patches-daemon-bpf bot deleted the series/978263=>bpf-next branch July 5, 2025 22:35
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