From patchwork Thu Oct 13 11:11:29 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Maryam Tahhan X-Patchwork-Id: 13005843 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2345FC4332F for ; Thu, 13 Oct 2022 10:16:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229469AbiJMKQH (ORCPT ); Thu, 13 Oct 2022 06:16:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40322 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229618AbiJMKQF (ORCPT ); Thu, 13 Oct 2022 06:16:05 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0B1DFEA6AE for ; Thu, 13 Oct 2022 03:16:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1665656163; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ZyOh5IE5da6lzhgTjUAARlUOlXyArSrFTePf4CQIznI=; b=Ifr5pASYLzJC1Bf4y251ZB/Dzg+N/Hn1NLY2xQ2bOlx2VXfgbb+Ndb5ptxk4b798O5nOa8 y5Yf1Fwdykb3XtrZCszzVXtRF2b5dRxFzpJk11wwme9Gqna/QFk5xe1MB/+Z7ovtD38pIk B8UKiUjO4amMO1azRCI9U97J1N5CP3k= Received: from mail-oa1-f69.google.com (mail-oa1-f69.google.com [209.85.160.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-564-LH9Mkv9gMXG3ILoebfX_Bg-1; Thu, 13 Oct 2022 06:16:02 -0400 X-MC-Unique: LH9Mkv9gMXG3ILoebfX_Bg-1 Received: by mail-oa1-f69.google.com with SMTP id 586e51a60fabf-132e28ef8faso907203fac.0 for ; Thu, 13 Oct 2022 03:16:02 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=ZyOh5IE5da6lzhgTjUAARlUOlXyArSrFTePf4CQIznI=; b=HhKeZSjvWQs6OX7/gcU80hdDU4MxGbqtWvyy011OtZgZu0bHRy/Z+HhETbQGVGkOp2 9nWNm+x+Lb/MNf9tWx5/daH7yoAsu0SXJAyh1axa9Kz99k5eTEZezqCjBz4L+FASeRn0 ut5Hb2SiCNPjqRCbtzD6lEwnMO6Nmt+sKpZ0HcI2EoPyI1d6N3jVqAjyGUoyXHqKF0zr 1DnSoF2m0oUsoyDWjTkPaL8+8H3WP9a0E87LA/h2xZiIJltoxWe7QLNsayj+RWf3JwVH bF6RxOWgwASjiSRS/B/Pv8NGdwcIF4zsfp+M7mY8r8d+IXtqPn/+xfGEhSkrVUjTrqVe Hiyg== X-Gm-Message-State: ACrzQf1Y1KfYfKZReme6qP1DXZKWP58LOyfGqBfCHImyMP4kD4cCkw8A Ob0ik533mOhcMBkFC/WpdwwkW243q4x53VAeBiQCbQc1EUcNZDoQ0/LI4hDiVWDZMsWurbRa6km V7uHjr9d1iptNQrS6Kpicyupeodj8/9t1RlMc1HiA/LEg+BWPvCkWl3EzkAdQvc4= X-Received: by 2002:a05:6808:e90:b0:345:49f2:a112 with SMTP id k16-20020a0568080e9000b0034549f2a112mr4282889oil.7.1665656161267; Thu, 13 Oct 2022 03:16:01 -0700 (PDT) X-Google-Smtp-Source: AMsMyM787W3E+iseBE3MbhxdvuNVMEUfi7cpcQQ0u01921AkDHI0tmAn8dW8UjlKa99DEMdM+oLd4Q== X-Received: by 2002:a05:6808:e90:b0:345:49f2:a112 with SMTP id k16-20020a0568080e9000b0034549f2a112mr4282871oil.7.1665656160834; Thu, 13 Oct 2022 03:16:00 -0700 (PDT) Received: from nfvsdn-06.testing.baremetal.edge-sites.net (nat-pool-232-132.redhat.com. [66.187.232.132]) by smtp.gmail.com with ESMTPSA id f187-20020aca38c4000000b00354732338desm5034605oia.17.2022.10.13.03.16.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Oct 2022 03:16:00 -0700 (PDT) From: mtahhan@redhat.com To: bpf@vger.kernel.org, linux-doc@vger.kernel.org Cc: Maryam Tahhan Subject: [PATCH bpf-next v2 1/1] doc: DEVMAPs and XDP_REDIRECT Date: Thu, 13 Oct 2022 07:11:29 -0400 Message-Id: <20221013111129.401325-2-mtahhan@redhat.com> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20221013111129.401325-1-mtahhan@redhat.com> References: <20221013111129.401325-1-mtahhan@redhat.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net From: Maryam Tahhan Add documentation for BPF_MAP_TYPE_DEVMAP and BPF_MAP_TYPE_DEVMAP_HASH including kernel version introduced, usage and examples. Add documentation that describes XDP_REDIRECT. Signed-off-by: Maryam Tahhan --- Documentation/bpf/index.rst | 1 + Documentation/bpf/map_devmap.rst | 192 +++++++++++++++++++++++++++++++ Documentation/bpf/redirect.rst | 46 ++++++++ 3 files changed, 239 insertions(+) create mode 100644 Documentation/bpf/map_devmap.rst create mode 100644 Documentation/bpf/redirect.rst diff --git a/Documentation/bpf/index.rst b/Documentation/bpf/index.rst index 1b50de1983ee..1088d44634d6 100644 --- a/Documentation/bpf/index.rst +++ b/Documentation/bpf/index.rst @@ -29,6 +29,7 @@ that goes into great technical depth about the BPF Architecture. clang-notes linux-notes other + redirect .. only:: subproject and html diff --git a/Documentation/bpf/map_devmap.rst b/Documentation/bpf/map_devmap.rst new file mode 100644 index 000000000000..bdba55640f4c --- /dev/null +++ b/Documentation/bpf/map_devmap.rst @@ -0,0 +1,192 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. Copyright (C) 2022 Red Hat, Inc. + +================================================= +BPF_MAP_TYPE_DEVMAP and BPF_MAP_TYPE_DEVMAP_HASH +================================================= + +.. note:: + - ``BPF_MAP_TYPE_DEVMAP`` was introduced in kernel version 4.14 + - ``BPF_MAP_TYPE_DEVMAP_HASH`` was introduced in kernel version 5.4 + +``BPF_MAP_TYPE_DEVMAP`` and ``BPF_MAP_TYPE_DEVMAP_HASH`` are BPF maps primarily +used as backend maps for the XDP BPF helper call ``bpf_redirect_map()``. +``BPF_MAP_TYPE_DEVMAP`` is backed by an array that uses the key as +the index to lookup a reference to a net device. While ``BPF_MAP_TYPE_DEVMAP_HASH`` +is backed by a hash table that uses the ``ifindex`` as the key to lookup a reference +to a net device. The user provides either <``key``/ ``ifindex``> or +<``key``/ ``struct bpf_devmap_val``> pairs to update the maps with new net devices. + +.. note:: + While ``BPF_MAP_TYPE_DEVMAP_HASH`` allows for densely packing the net devices + it comes at the cost of a hash of the key when performing a look up. + +The setup and packet enqueue/send code is shared between the two types of +devmap; only the lookup and insertion is different. + +Usage +===== + +.. c:function:: + long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags) + + Net device entries can be added or updated using the ``bpf_map_update_elem()`` + helper. This helper replaces existing elements atomically. The ``value`` parameter + can be ``struct bpf_devmap_val`` or a simple ``int ifindex`` for backwards + compatibility. + +.. note:: + The maps can only be updated from user space and not from a BPF program. + + .. code-block:: c + + struct bpf_devmap_val { + __u32 ifindex; /* device index */ + union { + int fd; /* prog fd on map write */ + __u32 id; /* prog id on map read */ + } bpf_prog; + }; + + DEVMAPs can associate a program with a device entry by adding a ``bpf_prog.fd`` + to ``struct bpf_devmap_val``. Programs are run after ``XDP_REDIRECT`` and have + access to both Rx device and Tx device. The program associated with the ``fd`` + must have type XDP with expected attach type ``xdp_devmap``. + When a program is associated with a device index, the program is run on an + ``XDP_REDIRECT`` and before the buffer is added to the per-cpu queue. Examples + of how to attach/use xdp_devmap progs can be found in the kernel selftests: + + - test_xdp_with_devmap_helpers_ + - xdp_devmap_attach_ + +.. _xdp_devmap_attach: https://github.com/torvalds/linux/blob/master/tools/testing/selftests/bpf/prog_tests/xdp_devmap_attach.c +.. _test_xdp_with_devmap_helpers: https://github.com/torvalds/linux/blob/master/tools/testing/selftests/bpf/progs/test_xdp_with_devmap_helpers.c + +.. c:function:: + void *bpf_map_lookup_elem(struct bpf_map *map, const void *key) + + net device entries can be retrieved using the ``bpf_map_lookup_elem()`` + helper. + +.. c:function:: + long bpf_map_delete_elem(struct bpf_map *map, const void *key) + + net device entries can be deleted using the ``bpf_map_delete_elem()`` + helper. This helper will return 0 on success, or negative error in case of + failure. + +.. c:function:: + long bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags) + + Redirect the packet to the endpoint referenced by ``map`` at index ``key``. + For ``BPF_MAP_TYPE_DEVMAP`` and ``BPF_MAP_TYPE_DEVMAP_HASH`` this map contains + references to net devices (for forwarding packets through other ports). + + The lower two bits of *flags* are used as the return code if the map lookup + fails. This is so that the return value can be one of the XDP program return + codes up to ``XDP_TX``, as chosen by the caller. The higher bits of ``flags`` + can be set to ``BPF_F_BROADCAST`` or ``BPF_F_EXCLUDE_INGRESS`` as defined + below. + + With ``BPF_F_BROADCAST`` the packet will be broadcast to all the interfaces + in the map, with ``BPF_F_EXCLUDE_INGRESS`` the ingress interface will be excluded + from the broadcast. + + This helper will return ``XDP_REDIRECT`` on success, or the value of the two + lower bits of the *flags* argument if the map lookup fails. + + More information about redirection can be found :doc:`redirect` + +Examples +======== + +Kernel BPF +---------- + +The following code snippet shows how to declare a ``BPF_MAP_TYPE_DEVMAP`` +called tx_port. + +.. code-block:: c + + struct { + __uint(type, BPF_MAP_TYPE_DEVMAP); + __type(key, __u32); + __type(value, __u32); + __uint(max_entries, 256); + } tx_port SEC(".maps"); + +The following code snippet shows how to declare a ``BPF_MAP_TYPE_DEVMAP_HASH`` +called forward_map. + +.. code-block:: c + + struct { + __uint(type, BPF_MAP_TYPE_DEVMAP_HASH); + __type(key, __u32); + __type(value, struct bpf_devmap_val); + __uint(max_entries, 32); + } forward_map SEC(".maps"); + +.. note:: + + The value type in the DEVMAP above is a ``struct bpf_devmap_val`` + +The following code snippet shows a simple xdp_redirect_map program. This program +would work with a user space program that populates the devmap ``tx_port`` based +on ingress ifindexes. The BPF program (below) is redirecting packets using the +ingress ifindex as the ``key``. + +.. code-block:: c + + SEC("xdp") + int xdp_redirect_map_func(struct xdp_md *ctx) + { + int index = ctx->ingress_ifindex; + + return bpf_redirect_map(&tx_port, index, BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS); + } + + +User space +---------- + +The following code snippet shows how to update a devmap called ``tx_port``. + +.. code-block:: c + + int update_devmap(int ifindex, int redirect_ifindex) + { + int ret = -1; + + ret = bpf_map_update_elem(bpf_map__fd(tx_port), &ifindex, &redirect_ifindex, 0); + if (ret < 0) { + fprintf(stderr, "Failed to update devmap_ value: %s\n", + strerror(errno)); + } + + return ret; + } + +The following code snippet shows how to update a hash_devmap called ``forward_map``. + +.. code-block:: c + + int update_devmap(int ifindex, int redirect_ifindex) + { + struct bpf_devmap_val devmap_val = { .ifindex = redirect_ifindex }; + int ret = -1; + + ret = bpf_map_update_elem(bpf_map__fd(forward_map), &ifindex, &devmap_val, 0); + if (ret < 0) { + fprintf(stderr, "Failed to update devmap_ value: %s\n", + strerror(errno)); + } + return ret; + } + +References +=========== + +- https://lwn.net/Articles/728146/ +- https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=6f9d451ab1a33728adb72d7ff66a7b374d665176 +- https://elixir.bootlin.com/linux/latest/source/net/core/filter.c#L4106 diff --git a/Documentation/bpf/redirect.rst b/Documentation/bpf/redirect.rst new file mode 100644 index 000000000000..5a0377a67ff0 --- /dev/null +++ b/Documentation/bpf/redirect.rst @@ -0,0 +1,46 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. Copyright (C) 2022 Red Hat, Inc. + +============ +XDP_REDIRECT +============ + +XDP_REDIRECT works by a three-step process, implemented as follows: + +1. The ``bpf_redirect()`` and ``bpf_redirect_map()`` helpers will lookup the + target of the redirect and store it (along with some other metadata) in a + per-CPU ``struct bpf_redirect_info``. This is where the maps above come into + play. + +2. When the program returns the ``XDP_REDIRECT`` return code, the driver will + call ``xdp_do_redirect()`` which will use the information in ``struct + bpf_redirect_info`` to actually enqueue the frame into a map type-specific + bulk queue structure. + +3. Before exiting its NAPI poll loop, the driver will call ``xdp_do_flush()``, + which will flush all the different bulk queues, thus completing the + redirect. + +Pointers to the map entries will be kept around for this whole sequence of +steps, protected by RCU. However, there is no top-level ``rcu_read_lock()`` in +the core code; instead, the RCU protection relies on everything happening +inside a single NAPI poll sequence. + +.. note:: + Not all drivers support transmitting frames after a redirect, and for + those that do, not all of them support non-linear frames. Non-linear xdp + bufs/frames are bufs/frames that contain more than one fragment. + +XDP_REDIRECT works with the following map types: + +- BPF_MAP_TYPE_DEVMAP +- BPF_MAP_TYPE_DEVMAP_HASH +- BPF_MAP_TYPE_CPUMAP +- BPF_MAP_TYPE_XSKMAP + +For more information on these maps, please see the specific map documentation. + +References +=========== + +- https://elixir.bootlin.com/linux/latest/source/net/core/filter.c#L4106