From mboxrd@z Thu Jan 1 00:00:00 1970 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, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham 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 A2453C169C2 for ; Wed, 20 Jan 2021 21:09:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 722F0235F7 for ; Wed, 20 Jan 2021 21:09:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2436638AbhATU73 (ORCPT ); Wed, 20 Jan 2021 15:59:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42514 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728821AbhATNlQ (ORCPT ); Wed, 20 Jan 2021 08:41:16 -0500 Received: from mail-wm1-x34a.google.com (mail-wm1-x34a.google.com [IPv6:2a00:1450:4864:20::34a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 92140C061794 for ; Wed, 20 Jan 2021 05:39:57 -0800 (PST) Received: by mail-wm1-x34a.google.com with SMTP id z188so1571115wme.1 for ; Wed, 20 Jan 2021 05:39:57 -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=6OdTPYEA2p5+e67drhVq+n88z8c6ioQj4MZmywIDAFM=; b=ANN34zi07ugZKnGspUDX8SGtW0gJFAepbGvNv79YXL+On+puhP5NhSPFqMbN8791sA +OpVHWkYimFLQYs5KnQaYv7MjAWS2Ul3AO2PWWUcbpB3s0mDPKyc6jmOhvURhuy9BCME 7kpqPpCOThFEQ5cUpS3oqyuDFVemFeDY5MopINLGdsmLvFRTquXUbYcHZqti718nZEHP VRFHQ/vZK/p00SHoUyQydfK8pTOND8ZEXE7zo4WTonNz09z3ICvSOQgDbHijvLOxpsDi r8cyrdeg6PviDgfUSKMZ1IrM0RZq83vxWevQNC5kHDZbU9VsdVIKMqJHihF82i8vSfQi agXg== 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=6OdTPYEA2p5+e67drhVq+n88z8c6ioQj4MZmywIDAFM=; b=V8gBn4llcul0sMVnMwAfTpSal/frA6g0Pyozb8kQ2Dv6T4OB7ObdxnEPM8+PKcuej4 0I6qphH092a0CUT030+3UoNIcGPMqGldRVR5+Pa+sqMuGbnwwzkur2wwLpFpOg8012Th wrH/s0M5euHg90+S8msDgD2b7/NwMdfHjGwWm8SUDsmOKHFLUi0eBB6VYHlrGLFGg+Tt OuNh6aYVW/UYaKbIBh+O1rOrMAg4phZ1pP+Qdtpt2j3a+wplfYrvdzSmNxuVfuSFUnZD xYSRoGVcZACDjogWwL3SJ20gixEk2x/NAVv0MJeeOsBVZnC+ur+OrDJrfc8QNtDb7XsK o2QA== X-Gm-Message-State: AOAM533VkSmrrzhWB4yN35dZgdMWsw0a7QMKthhUpO3WR7fqcxqFGskL tAhSkq3weacnd4kCrlqakdWgrUNg5ZQZ9A== X-Google-Smtp-Source: ABdhPJz+1pw/frS7iuoskUPl/0VZ5TsAWO9NiEYk8b+eCEfPZfzFbTli1vpPu9KhtHzz75ExuN5A1dfpBffEUg== Sender: "jackmanb via sendgmr" X-Received: from beeg.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:11db]) (user=jackmanb job=sendgmr) by 2002:a1c:81cc:: with SMTP id c195mr4398201wmd.70.1611149996346; Wed, 20 Jan 2021 05:39:56 -0800 (PST) Date: Wed, 20 Jan 2021 13:39:46 +0000 In-Reply-To: <20210120133946.2107897-1-jackmanb@google.com> Message-Id: <20210120133946.2107897-3-jackmanb@google.com> Mime-Version: 1.0 References: <20210120133946.2107897-1-jackmanb@google.com> X-Mailer: git-send-email 2.30.0.284.gd98b1dd5eaa7-goog Subject: [PATCH bpf-next v3 2/2] docs: bpf: Clarify -mcpu=v3 requirement for atomic ops From: Brendan Jackman To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , KP Singh , Florent Revest , Lukas Bulwahn , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Jonathan Corbet , Brendan Jackman Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alexei pointed out [1] that this wording is pretty confusing. Here's an attempt to be more explicit and clear. [1] https://lore.kernel.org/bpf/CAADnVQJVvwoZsE1K+6qRxzF7+6CvZNzygnoBW9tZNWJELk5c=Q@mail.gmail.com/T/#m07264fc18fdc43af02fc1320968afefcc73d96f4 Signed-off-by: Brendan Jackman --- Documentation/networking/filter.rst | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst index 4c2bb4c6364d..b3f457802836 100644 --- a/Documentation/networking/filter.rst +++ b/Documentation/networking/filter.rst @@ -1081,9 +1081,10 @@ 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 +Clang can generate atomic instructions by default when ``-mcpu=v3`` is +enabled. If a lower version for ``-mcpu`` is set, the only atomic instruction +Clang can generate is ``BPF_ADD`` *without* ``BPF_FETCH``. If you need to enable +the atomics features, while keeping a lower ``-mcpu`` version, you can use ``-Xclang -target-feature -Xclang +alu32``. You may encounter ``BPF_XADD`` - this is a legacy name for ``BPF_ATOMIC``, -- 2.30.0.284.gd98b1dd5eaa7-goog