From patchwork Thu Jan 14 18:17:51 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Brendan Jackman X-Patchwork-Id: 12020593 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 X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 68EE0C43331 for ; Thu, 14 Jan 2021 18:20:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3896323B6C for ; Thu, 14 Jan 2021 18:20:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726288AbhANSTs (ORCPT ); Thu, 14 Jan 2021 13:19:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58266 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729704AbhANSTp (ORCPT ); Thu, 14 Jan 2021 13:19:45 -0500 Received: from mail-wr1-x449.google.com (mail-wr1-x449.google.com [IPv6:2a00:1450:4864:20::449]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 504AAC0617A4 for ; Thu, 14 Jan 2021 10:18:32 -0800 (PST) Received: by mail-wr1-x449.google.com with SMTP id u14so2963116wrr.15 for ; Thu, 14 Jan 2021 10:18:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:in-reply-to:message-id:mime-version:references:subject :from:to:cc; bh=oW3at7tYerofWpFJJa0IT/4f63HRcTZEokqKQUOM8Tc=; b=ejJx5SL1fxsjwfzzDNBu77jDzM3gbctXjuLEXIC3R0xMOGwoQYZOxS2JvSgYX0pkXg BXiXTH+qpyB2ubLuXMn8VO3P+2XHRd9MeE137iyXchQPCm847DnT3AJKSiy4uwQZ1UI8 /Oc42tfCquYcp6sSW1If1t/HCdJA7h3Gflnw6EUDdo7t143KiehHYxwe9nJFVVMHJXIh V+h2JlzkAPAv+oDLUuRfL8H5N0x6CITgrNe7LQHEkdrh2qnu3ClCFI1R9cWo03OVfRPi muOfMn91THVE3jIZYdDlfpEEhfp5VUSXNRxf71aaJC0BGfUQP/EREaKjqRXlydjOrFBP mGUQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=oW3at7tYerofWpFJJa0IT/4f63HRcTZEokqKQUOM8Tc=; b=VEI/rEo6/2GsPygy9Fo7Jw9IZNi+NNkgmuxPPyDgAtVezhxdoBict6Cv+kuhfgtTP1 NbtJqfGCf75MB+xY3jSHhp7eJ05KZ/k8mza5HqCpauzgFCd2RiiQarE7A3j/ZJ4ah07m 7WOITHVlSC2S7G72u1ubqKuDw74Lv+x/sc8RgEUkEKHEe4UzztHowlbiD8QBaV/8xxic GJ+1QGg5qMB8IjO6SsGSpn4/eUlocOek7zwPkLfdHbpsJdye1dMNCpoi9fWK9oVgz5uK 7NBltKFvbVEBBQVHO4bAYE5a4RkoaITvx42szAW0c83V+JRVbkvYMzUegzu64hbGjeqs BQzg== X-Gm-Message-State: AOAM533lD6h2S7lIFOACmJEan0J/K1ybAn8xi9rabKPlGZdbVjHP782a 2VPgHUaqlnURl46mwDAMKrsfRzwUbFMLhmx7d4vU6y+dCgL4rQ2ikTXXdxoM9u3Ik8eZ25yjMYP nxRLnoqMVc4QE5A9H2Rq4a0+RhwBaZXWTjJFfxx8f67wLiJ+pBU7EL5ZoDKABN08= X-Google-Smtp-Source: ABdhPJwIi3mz/1SY+6oE7+tGQR4TG4Ys8wjpCeHeJPoKZHE0TxLj8pwGF4emyEHgJecZi38QdAkxaELMDCwY1w== Sender: "jackmanb via sendgmr" X-Received: from beeg.c.googlers.com ([fda3:e722:ac3:10:28:9cb1:c0a8:11db]) (user=jackmanb job=sendgmr) by 2002:adf:decd:: with SMTP id i13mr4665456wrn.144.1610648310534; Thu, 14 Jan 2021 10:18:30 -0800 (PST) Date: Thu, 14 Jan 2021 18:17:51 +0000 In-Reply-To: <20210114181751.768687-1-jackmanb@google.com> Message-Id: <20210114181751.768687-12-jackmanb@google.com> Mime-Version: 1.0 References: <20210114181751.768687-1-jackmanb@google.com> X-Mailer: git-send-email 2.30.0.284.gd98b1dd5eaa7-goog Subject: [PATCH bpf-next v7 11/11] bpf: Document new atomic instructions From: Brendan Jackman To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , KP Singh , Florent Revest , linux-kernel@vger.kernel.org, " =?utf-8?b?QmrDtnJuIFTDtnBlbA==?= " , John Fastabend , Yonghong Song , Brendan Jackman Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Document new atomic instructions. Acked-by: Yonghong Song Signed-off-by: Brendan Jackman --- Documentation/networking/filter.rst | 31 +++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst index 1583d59d806d..f6d8f90e9a56 100644 --- a/Documentation/networking/filter.rst +++ b/Documentation/networking/filter.rst @@ -1053,8 +1053,39 @@ encoding. .imm = BPF_ADD, .code = BPF_ATOMIC | BPF_W | BPF_STX: lock xadd *(u32 *)(dst_reg + off16) += src_reg .imm = BPF_ADD, .code = BPF_ATOMIC | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg +The basic atomic operations supported are: + + BPF_ADD + BPF_AND + BPF_OR + BPF_XOR + +Each having equivalent semantics with the ``BPF_ADD`` example, that is: the +memory location addresed by ``dst_reg + off`` is atomically modified, with +``src_reg`` as the other operand. If the ``BPF_FETCH`` flag is set in the +immediate, then these operations also overwrite ``src_reg`` with the +value that was in memory before it was modified. + +The more special operations are: + + BPF_XCHG + +This atomically exchanges ``src_reg`` with the value addressed by ``dst_reg + +off``. + + BPF_CMPXCHG + +This atomically compares the value addressed by ``dst_reg + off`` with +``R0``. If they match it is replaced with ``src_reg``, The value that was there +before is loaded back to ``R0``. + Note that 1 and 2 byte atomic operations are not supported. +Except ``BPF_ADD`` _without_ ``BPF_FETCH`` (for legacy reasons), all 4 byte +atomic operations require alu32 mode. Clang enables this mode by default in +architecture v3 (``-mcpu=v3``). For older versions it can be enabled with +``-Xclang -target-feature -Xclang +alu32``. + You may encounter BPF_XADD - this is a legacy name for BPF_ATOMIC, referring to the exclusive-add operation encoded when the immediate field is zero.