From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-x44a.google.com (mail-pf1-x44a.google.com [IPv6:2607:f8b0:4864:20::44a]) by mail.toke.dk (Postfix) with ESMTPS id 0EE1C9C4541 for ; Mon, 21 Nov 2022 19:25:57 +0100 (CET) Authentication-Results: mail.toke.dk; dkim=pass (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20210112 header.b=CSFHoG6g Received: by mail-pf1-x44a.google.com with SMTP id f189-20020a6238c6000000b0056e3400fdc0so7950238pfa.10 for ; Mon, 21 Nov 2022 10:25:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=HOzG/5dEM9DkbawI2NlOgkggkIO8cF5opRTpWfNApEg=; b=CSFHoG6gVZh4SBZCczWClLOJPtmruLeP1CVP4tX94SUl4kZuItSp3nkuM9V+pa4dUC Gim9gX92dMmq4n0R3k7w2ucPQQTGI9MUeok2ruJWffbwNRWCAfnXw+3hlYkyt1GmCDj1 DiDsj46t4OZ1/sEuKpRr+j/nt27flowaV+qpaLje5Q2coskhopWg40G2QmnNWED3gWaU 89LQ5MSr0YqpSrvlDXQsQJXhBZA0IvR01S7XWpQEgAPZBtcqy+KfIFBnI3oquvknnxzO 8F9StkDvJo9iX40ZMZT3K74lAMyJUgngpvaen+Svsqd/pLkdfwWnK+lokaY/uI11XWjf wMvw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=HOzG/5dEM9DkbawI2NlOgkggkIO8cF5opRTpWfNApEg=; b=0U81nPcmZKUxLDcca8ulPruore5B0nK+kr0P3gVuBWo7Gqn6T9kuHnsc5UsNb82mKE lAhmW7UA2cbqdn7bGSVdHdJcPZyqwxWdiS5BhaIFyQ5/11OsQ1/PMp5toevU21PATTwL xxUp7FRCAGjvFsQIMoII51B+AvISmDtlPuhByLhTOfbbthV6ZC39stcq1hTvW8drRv4G +FOVNLGHU9TIr5B+uykIpm9ZriVs9Ttn7qSooRQLp/jP9JrPckzwKCl5tWgkV003qIit n0eUdKjuENfLbWPZAvRvdZKv9Ty3zOaQwAnryeTCOxRer8+5pDWK5Yuf+TcuEBstLxYi KCqA== X-Gm-Message-State: ANoB5plA1as9m0I3xOWB0jfF5wUHWDqKwGIQGr+dYXGZI1OvrioW3Rw3 AGrACSTdeMown4b1EUMUkdKWfWQ= X-Google-Smtp-Source: AA0mqf4MB+oLIG61MneSZIxhA4uojAGlFL2tQV0bErJVWZ3UtpqMf1lMDnr+HVx2A3R6bARGixRNhjA= X-Received: from sdf.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5935]) (user=sdf job=sendgmr) by 2002:a17:90a:df8c:b0:20a:fee1:8f69 with SMTP id p12-20020a17090adf8c00b0020afee18f69mr1872407pjv.0.1669055155656; Mon, 21 Nov 2022 10:25:55 -0800 (PST) Date: Mon, 21 Nov 2022 10:25:45 -0800 In-Reply-To: <20221121182552.2152891-1-sdf@google.com> Mime-Version: 1.0 References: <20221121182552.2152891-1-sdf@google.com> X-Mailer: git-send-email 2.38.1.584.g0f3c55d4c2-goog Message-ID: <20221121182552.2152891-2-sdf@google.com> From: Stanislav Fomichev To: bpf@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Message-ID-Hash: 4M2XONOQVXKAL364OFZLT75OGIAQ4EGI X-Message-ID-Hash: 4M2XONOQVXKAL364OFZLT75OGIAQ4EGI X-MailFrom: 3s8J7YwMKCUo4prs00sxq.o0y9p1-tuz549p1-130vqo5.zq5@flex--sdf.bounces.google.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, David Ahern , Jakub Kicinski , Willem de Bruijn , Jesper Dangaard Brouer , Anatoly Burakov , Alexander Lobakin , Magnus Karlsson , Maryam Tahhan , xdp-hints@xdp-project.net, netdev@vger.kernel.org X-Mailman-Version: 3.3.7 Precedence: list Subject: [xdp-hints] [PATCH bpf-next v2 1/8] bpf: Document XDP RX metadata List-Id: XDP hardware hints design discussion Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: Document all current use-cases and assumptions. Cc: John Fastabend Cc: David Ahern Cc: Martin KaFai Lau Cc: Jakub Kicinski Cc: Willem de Bruijn Cc: Jesper Dangaard Brouer Cc: Anatoly Burakov Cc: Alexander Lobakin Cc: Magnus Karlsson Cc: Maryam Tahhan Cc: xdp-hints@xdp-project.net Cc: netdev@vger.kernel.org Signed-off-by: Stanislav Fomichev --- Documentation/bpf/xdp-rx-metadata.rst | 90 +++++++++++++++++++++++++++ 1 file changed, 90 insertions(+) create mode 100644 Documentation/bpf/xdp-rx-metadata.rst diff --git a/Documentation/bpf/xdp-rx-metadata.rst b/Documentation/bpf/xdp-rx-metadata.rst new file mode 100644 index 000000000000..498eae718275 --- /dev/null +++ b/Documentation/bpf/xdp-rx-metadata.rst @@ -0,0 +1,90 @@ +=============== +XDP RX Metadata +=============== + +XDP programs support creating and passing custom metadata via +``bpf_xdp_adjust_meta``. This metadata can be consumed by the following +entities: + +1. ``AF_XDP`` consumer. +2. Kernel core stack via ``XDP_PASS``. +3. Another device via ``bpf_redirect_map``. +4. Other BPF programs via ``bpf_tail_call``. + +General Design +============== + +XDP has access to a set of kfuncs to manipulate the metadata. Every +device driver implements these kfuncs. The set of kfuncs is +declared in ``include/net/xdp.h`` via ``XDP_METADATA_KFUNC_xxx``. + +Currently, the following kfuncs are supported. In the future, as more +metadata is supported, this set will grow: + +- ``bpf_xdp_metadata_rx_timestamp_supported`` returns true/false to + indicate whether the device supports RX timestamps +- ``bpf_xdp_metadata_rx_timestamp`` returns packet RX timestamp +- ``bpf_xdp_metadata_rx_hash_supported`` returns true/false to + indicate whether the device supports RX hash +- ``bpf_xdp_metadata_rx_hash`` returns packet RX hash + +Within the XDP frame, the metadata layout is as follows:: + + +----------+-----------------+------+ + | headroom | custom metadata | data | + +----------+-----------------+------+ + ^ ^ + | | + xdp_buff->data_meta xdp_buff->data + +AF_XDP +====== + +``AF_XDP`` use-case implies that there is a contract between the BPF program +that redirects XDP frames into the ``XSK`` and the final consumer. +Thus the BPF program manually allocates a fixed number of +bytes out of metadata via ``bpf_xdp_adjust_meta`` and calls a subset +of kfuncs to populate it. User-space ``XSK`` consumer, looks +at ``xsk_umem__get_data() - METADATA_SIZE`` to locate its metadata. + +Here is the ``AF_XDP`` consumer layout (note missing ``data_meta`` pointer):: + + +----------+-----------------+------+ + | headroom | custom metadata | data | + +----------+-----------------+------+ + ^ + | + rx_desc->address + +XDP_PASS +======== + +This is the path where the packets processed by the XDP program are passed +into the kernel. The kernel creates ``skb`` out of the ``xdp_buff`` contents. +Currently, every driver has a custom kernel code to parse the descriptors and +populate ``skb`` metadata when doing this ``xdp_buff->skb`` conversion. +In the future, we'd like to support a case where XDP program can override +some of that metadata. + +The plan of record is to make this path similar to ``bpf_redirect_map`` +so the program can control which metadata is passed to the skb layer. + +bpf_redirect_map +================ + +``bpf_redirect_map`` can redirect the frame to a different device. +In this case we don't know ahead of time whether that final consumer +will further redirect to an ``XSK`` or pass it to the kernel via ``XDP_PASS``. +Additionally, the final consumer doesn't have access to the original +hardware descriptor and can't access any of the original metadata. + +For this use-case, only custom metadata is currently supported. If +the frame is eventually passed to the kernel, the skb created from such +a frame won't have any skb metadata. The ``XSK`` consumer will only +have access to the custom metadata. + +bpf_tail_call +============= + +No special handling here. Tail-called program operates on the same context +as the original one. -- 2.38.1.584.g0f3c55d4c2-goog