From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9C8241BC3F; Tue, 3 Jun 2025 17:46:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748972800; cv=none; b=tnGmOn+IdPNP0mcxM8VVCTUWjrXGk1r9IJq7dhho0ThGQQ9E/uBxC5WwnX3SwNb3FYYYMK2E7KOhbj6PSlFGAzalVjlwhng1HywKOV3Nnj4HL93Sj2Tm/mWg1otR6OIHlEF8Nn72aPmPOmtE0sKP5KznAtkDLGOdH3R+lvYo7dw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748972800; c=relaxed/simple; bh=qHI5lmVU9Uhwmq5FhfYhc3yzSOkYxipHvNmhX2wCH8I=; h=Subject:From:To:Cc:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=M2YCXkJVWVmziSW/tdxOLkSetWai/0m4plVcAvoDRVJyBY7IUsnj2kUh1ktpDlCtyrZP3kR+gPKDWrJs818ybPHTvb5l/oaRt7uKgbDmBRTpbQ3K0Vp/81+WymOS8CjuzXSwtWOiSWcl2mD0yjVtgdG2fhHrNVQWV6ulkTWjGSE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=o0zGgVA+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="o0zGgVA+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 050A6C4CEED; Tue, 3 Jun 2025 17:46:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748972800; bh=qHI5lmVU9Uhwmq5FhfYhc3yzSOkYxipHvNmhX2wCH8I=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=o0zGgVA+T9oSLzVwOGQIc19Flu1KlhQGv0n3cQBNhiFbC3UpX0pWRgoD5Z9KkNwvZ PcH374ZDBYzCNRtzD/GHqDk70X+Zdyr90ISdExR7wRzUPb4rWLryAG/8Rfu3ptFZhA qQaG2CcqI3X5oJNv06Kzo32GxxyAeVNNXxpSU4fo6EqSRW91wQxgDNjM8FrdkYj8Ri wG7X/3riKrcXHb/ke0Dy5SA/vnAUDYAe0tyzvRxZS4FHHHEN63+Dy1wpwHNVxisiBZ ogbcc8rwnXP9ppK2el9S4hHoGMQnPuIv7hwED4u//SShvlz+PsRslkRv5ja9/2ZrQj KVlBFpU7i8rZw== Subject: [PATCH bpf-next V1 7/7] net: xdp: update documentation for xdp-rx-metadata.rst From: Jesper Dangaard Brouer To: bpf@vger.kernel.org, netdev@vger.kernel.org, Jakub Kicinski , lorenzo@kernel.org Cc: Jesper Dangaard Brouer , Alexei Starovoitov , Daniel Borkmann , Eric Dumazet , "David S. Miller" , Paolo Abeni , sdf@fomichev.me, kernel-team@cloudflare.com, arthur@arthurfabre.com, jakub@cloudflare.com Date: Tue, 03 Jun 2025 19:46:35 +0200 Message-ID: <174897279518.1677018.5982630277641723936.stgit@firesoul> In-Reply-To: <174897271826.1677018.9096866882347745168.stgit@firesoul> References: <174897271826.1677018.9096866882347745168.stgit@firesoul> User-Agent: StGit/1.5 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit 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 --- Documentation/networking/xdp-rx-metadata.rst | 74 ++++++++++++++++++++------ net/core/xdp.c | 32 +++++++++++ 2 files changed, 90 insertions(+), 16 deletions(-) diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst index a6e0ece18be5..2c54208e4f7e 100644 --- a/Documentation/networking/xdp-rx-metadata.rst +++ b/Documentation/networking/xdp-rx-metadata.rst @@ -90,22 +90,64 @@ the ``data_meta`` pointer. In the future, we'd like to support a case where an XDP program can override some of the metadata used for building ``skbs``. -bpf_redirect_map -================ - -``bpf_redirect_map`` can redirect the frame to a different device. -Some devices (like virtual ethernet links) support running a second XDP -program after the redirect. However, the final consumer doesn't have -access to the original hardware descriptor and can't access any of -the original metadata. The same applies to XDP programs installed -into devmaps and cpumaps. - -This means that for redirected packets only custom metadata is -currently supported, which has to be prepared by the initial XDP program -before redirect. If the frame is eventually passed to the kernel, the -``skb`` created from such a frame won't have any hardware metadata populated -in its ``skb``. If such a packet is later redirected into an ``XSK``, -that will also only have access to the custom metadata. +XDP_REDIRECT +============ + +The ``XDP_REDIRECT`` action forwards an XDP frame to another net device or a CPU +(via cpumap/devmap) for further processing. It is invoked using BPF helpers like +``bpf_redirect_map()`` or ``bpf_redirect()``. When an XDP frame is redirected, +the recipient (e.g., an XDP program on a veth device, or the kernel stack via +cpumap) loses direct access to the original NIC's hardware descriptor and thus +its hardware metadata + +By default, this loss of access means that if an ``xdp_frame`` is redirected and +then converted to an ``skb``, its ``skb`` fields for hardware-derived metadata +(like ``skb->hash`` or VLAN info) are not populated from the original +packet. This can impact features like Generic Receive Offload (GRO). While XDP +programs can manually save custom data (e.g., using ``bpf_xdp_adjust_meta()``), +propagating specific *hardware* RX hints to ``skb`` creation requires using the +kfuncs described below. + +To enable propagating selected hardware RX hints, store BPF kfuncs allow an +XDP program on the initial NIC to read these hints and then explicitly +*store* them. The kfuncs place this metadata in locations associated with +the XDP packet buffer, making it available if an ``skb`` is later built or +the frame is otherwise processed. For instance, RX hash and VLAN tags are +stored within the XDP frame's addressable headroom, while RX timestamps are +typically written to an area corresponding to ``skb_shared_info``. + +**Crucially, the BPF programmer must call these "store" kfuncs to save the +desired hardware hints for propagation.** The system does not do this +automatically. The NIC driver is responsible for ensuring sufficient headroom is +available; kfuncs may return ``-ENOSPC`` if space is inadequate for storing +these hints. + +When these kfuncs are used to store hints before redirection: + +* If the ``xdp_frame`` is converted to an ``skb``, the networking stack can use + the stored hints to populate ``skb`` fields (e.g., ``skb->hash``, + ``skb->vlan_tci``, timestamps), aiding netstack features like GRO. +* When running a second XDP-program after the redirect. The veth driver supports + access to the previous stored metadata is accessed though the normal reader + kfuncs. + +Kfuncs are available for storing RX hash (``bpf_xdp_store_rx_hash()``), +VLAN information (``bpf_xdp_store_rx_vlan()``), and hardware timestamps +(``bpf_xdp_store_rx_ts()``). Consult the kfunc API documentation for usage +details, expected data, return codes, and relevant XDP flags that may +indicate success or metadata availability. + +Kfuncs for **store** operations: + +.. kernel-doc:: net/core/xdp.c + :identifiers: bpf_xdp_store_rx_timestamp + +.. kernel-doc:: net/core/xdp.c + :identifiers: bpf_xdp_store_rx_hash + +.. kernel-doc:: net/core/xdp.c + :identifiers: bpf_xdp_store_rx_vlan_tag + bpf_tail_call ============= diff --git a/net/core/xdp.c b/net/core/xdp.c index 69077cf4c541..1c0f5f980394 100644 --- a/net/core/xdp.c +++ b/net/core/xdp.c @@ -984,6 +984,18 @@ __bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx, return -EOPNOTSUPP; } +/** + * bpf_xdp_store_rx_hash - Store XDP frame RX hash. + * @ctx: XDP context pointer. + * @hash: 32-bit hash value. + * @rss_type: RSS hash type. + * + * The RSS hash type (@rss_type) is as descibed in bpf_xdp_metadata_rx_hash. + * + * Return: + * * Returns 0 on success or ``-errno`` on error. + * * ``-NOSPC`` : means device driver doesn't provide enough headroom for storing + */ __bpf_kfunc int bpf_xdp_store_rx_hash(struct xdp_md *ctx, u32 hash, enum xdp_rss_hash_type rss_type) { @@ -999,6 +1011,18 @@ __bpf_kfunc int bpf_xdp_store_rx_hash(struct xdp_md *ctx, u32 hash, return 0; } +/** + * bpf_xdp_store_rx_vlan_tag - Store XDP packet outermost VLAN tag + * @ctx: XDP context pointer. + * @vlan_proto: VLAN protocol stored in **network byte order (BE)** + * @vlan_tci: VLAN TCI (VID + DEI + PCP) stored in **host byte order** + * + * See bpf_xdp_metadata_rx_vlan_tag() for byte order reasoning. + * + * Return: + * * Returns 0 on success or ``-errno`` on error. + * * ``-NOSPC`` : means device driver doesn't provide enough headroom for storing + */ __bpf_kfunc int bpf_xdp_store_rx_vlan(struct xdp_md *ctx, __be16 vlan_proto, u16 vlan_tci) { @@ -1014,6 +1038,14 @@ __bpf_kfunc int bpf_xdp_store_rx_vlan(struct xdp_md *ctx, __be16 vlan_proto, return 0; } +/** + * bpf_xdp_metadata_rx_timestamp - Store XDP frame RX timestamp. + * @ctx: XDP context pointer. + * @timestamp: Timestamp value. + * + * Return: + * * Returns 0 on success or ``-errno`` on error. + */ __bpf_kfunc int bpf_xdp_store_rx_ts(struct xdp_md *ctx, u64 ts) { struct xdp_buff *xdp = (struct xdp_buff *)ctx;