On 17/07/2025 11.19, Jakub Sitnicki wrote:
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:
I agree, that calling it META_AREA can easily be misunderstood and
confused with metadata or data_meta.
What do you think about renaming this to "hints" ?
E.g. XDP_FLAGS_HINTS_AREA
or XDP_FLAGS_HINTS_AVAIL
And also renaming XDP_FLAGS_META_RX_* to
e.g XDP_FLAGS_META_RX_HASH -> XDP_FLAGS_HINT_RX_HASH
or XDP_FLAGS_HW_HINT_RX_HASH
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 */
};
[...]
