On Wed, Jul 02, 2025 at 04:58 PM +02, Jesper Dangaard Brouer wrote:
> From: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
>
> 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 <lorenzo@xxxxxxxxxx>
> Signed-off-by: Jesper Dangaard Brouer <hawk@xxxxxxxxxx>
> ---
> include/net/xdp.h | 57 +++++++++++++++++++++++++++++++++++------------
> net/core/xdp.c | 1 +
> net/xdp/xsk_buff_pool.c | 4 ++-
> 3 files changed, 47 insertions(+), 15 deletions(-)
>
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index b40f1f96cb11..f52742a25212 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -71,11 +71,31 @@ struct xdp_txq_info {
> struct net_device *dev;
> };
>
> +struct xdp_rx_meta {
> + struct xdp_rx_meta_hash {
> + u32 val;
> + u32 type; /* enum xdp_rss_hash_type */
> + } hash;
> + struct xdp_rx_meta_vlan {
> + __be16 proto;
> + u16 tci;
> + } vlan;
> +};
> +
> +/* Storage area for HW RX metadata only available with reasonable headroom
> + * available. Less than XDP_PACKET_HEADROOM due to Intel drivers.
> + */
> +#define XDP_MIN_HEADROOM 192
> +
> enum xdp_buff_flags {
> XDP_FLAGS_HAS_FRAGS = BIT(0), /* non-linear xdp buff */
> XDP_FLAGS_FRAGS_PF_MEMALLOC = BIT(1), /* xdp paged memory is under
> * pressure
> */
> + XDP_FLAGS_META_AREA = BIT(2), /* storage area available */
Idea: Perhaps this could be called *HW*_META_AREA to differentiate from
the existing custom metadata area:
https://docs.kernel.org/networking/xdp-rx-metadata.html#af-xdp
> + XDP_FLAGS_META_RX_HASH = BIT(3), /* hw rx hash */
> + XDP_FLAGS_META_RX_VLAN = BIT(4), /* hw rx vlan */
> + XDP_FLAGS_META_RX_TS = BIT(5), /* hw rx timestamp */
> };
>
[...]
