From patchwork Thu Dec 3 16:02:45 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Brendan Jackman X-Patchwork-Id: 11949079 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, 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 0DA90C0018C for ; Thu, 3 Dec 2020 16:05:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AC15A207AA for ; Thu, 3 Dec 2020 16:05:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731207AbgLCQFP (ORCPT ); Thu, 3 Dec 2020 11:05:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54948 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729272AbgLCQFO (ORCPT ); Thu, 3 Dec 2020 11:05:14 -0500 Received: from mail-qv1-xf49.google.com (mail-qv1-xf49.google.com [IPv6:2607:f8b0:4864:20::f49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7F3AEC094251 for ; Thu, 3 Dec 2020 08:03:43 -0800 (PST) Received: by mail-qv1-xf49.google.com with SMTP id y8so1959570qvu.22 for ; Thu, 03 Dec 2020 08:03:43 -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=+oJt4YN1vV8BikzJk8T4MnuRoPet/ONJM85/l1oaFsA=; b=fVN2tNQLNEwDBCS0z2Ugrc7Z322KowXofgwiQ9YEdeV/KCt2OGr2VBVa1EMDEa3wKz YpU4Ba+Cl9MxtT2dEJYg5FdMcHTjj+6fBROVSB/N+NSL0TiLW2mHwqpo8ifxLtEZdrD+ x6P66T34hNWOrJKcGHbv30mOOjKtNiOFoExyWjKuAxS5djB+RtMiBt7GhEBLLZmKKHfl Md5+jyELCFNLSaecee9i0NHD+EcOtPwqyRNlPsuXVZ3P88OJm/Zhyt6gjKgapTAQ/79f FBvvYqNEbTpfZY7SzjM3k9cEX9dCDVEtrwx1ftqs398vsjI90tGKgDpMAGHK1AY5ZvjS Vr+g== 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=+oJt4YN1vV8BikzJk8T4MnuRoPet/ONJM85/l1oaFsA=; b=mhQVvrg/F3Voh8sWudidP5bECbCq/+Fmk8srSR/2GSKQRMO1c0lMf5gC6PqJDssdnW rAvDWl7pFdXMSi2zr+0TIQdA7uqm0jnEb+VHMhZouuZns4PEqcfwwOHX2t9CZEOYdd/Z t5l5P9mqlqzQPxvcFlYNQQERmoqydG6IgQhyDGLhhbj85usiEnJae9tn0b7fiDiQ4l8l QwrwJfN6W3X7BZ2eOY+jwr8vtx8x5pGgjRRjbf5DhSBHcCFKqCt44sXAKDV66bbTE960 CjvrrbcOAEroIMci6Fyc/eHQr8QkDNUgkRi2a2OojnvVJzTkwp9QFelPVhe8pK4Lv/iL KtWg== X-Gm-Message-State: AOAM530rCPXP610iA5b/bF0q2qHJeSHbwbuQ05ZWjtxKK/kdV9JJzjXB 0pgo9xBxn4QS28qHkD9WvjBH66a1gbITdQV56vZFoXXejZUWpjtoN+TfGOqtQpW65xdoWlM4eEq aFhTc9xvdB0xZZHbJBuP1pV79p4/9UdNf2sY+mhuokjq9TLpYqA2HXXASZskI4WI= X-Google-Smtp-Source: ABdhPJzEd1nsztwyeAv0SEjKx8FK75ZZ+DgtqH3y1CX08lYeGnBAHDonB2nICe8xfwm8dnQc5SWESwtNDMWl4Q== 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:a0c:9d07:: with SMTP id m7mr4069974qvf.5.1607011422530; Thu, 03 Dec 2020 08:03:42 -0800 (PST) Date: Thu, 3 Dec 2020 16:02:45 +0000 In-Reply-To: <20201203160245.1014867-1-jackmanb@google.com> Message-Id: <20201203160245.1014867-15-jackmanb@google.com> Mime-Version: 1.0 References: <20201203160245.1014867-1-jackmanb@google.com> X-Mailer: git-send-email 2.29.2.454.gaff20da3a2-goog Subject: [PATCH bpf-next v3 14/14] bpf: Document new atomic instructions From: Brendan Jackman To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Yonghong Song , Daniel Borkmann , KP Singh , Florent Revest , linux-kernel@vger.kernel.org, Jann Horn , Brendan Jackman Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Change-Id: Ic70fe9e3cb4403df4eb3be2ea5ae5af53156559e Signed-off-by: Brendan Jackman --- Documentation/networking/filter.rst | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst index 1583d59d806d..26d508a5e038 100644 --- a/Documentation/networking/filter.rst +++ b/Documentation/networking/filter.rst @@ -1053,6 +1053,32 @@ 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 (from architecture v4 onwards) 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. You may encounter BPF_XADD - this is a legacy name for BPF_ATOMIC, referring to