From patchwork Tue Jan 12 15:42:35 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Brendan Jackman X-Patchwork-Id: 12013835 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 93BEAC43333 for ; Tue, 12 Jan 2021 15:44:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5F13923131 for ; Tue, 12 Jan 2021 15:44:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390744AbhALPor (ORCPT ); Tue, 12 Jan 2021 10:44:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53090 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405332AbhALPom (ORCPT ); Tue, 12 Jan 2021 10:44:42 -0500 Received: from mail-wm1-x349.google.com (mail-wm1-x349.google.com [IPv6:2a00:1450:4864:20::349]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A5244C061382 for ; Tue, 12 Jan 2021 07:43:04 -0800 (PST) Received: by mail-wm1-x349.google.com with SMTP id g82so634551wmg.6 for ; Tue, 12 Jan 2021 07:43:04 -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=pp1KxffCDPqB9jIy9tx75GpgmaQQZyM9ktvJ18nRXiTSgY7iOlYcn/aLrbZzWn9QhQ J/ttqRDHk0CFmqUEVoF/OXmko556O047ZO0EVK9glyXSWKTuMLlQorx/q78jwJ26WHz5 a7jiDA1y0IMP/vKZh3ImwFFrYjN6o0PMJNeb8vxYLINl4WR9fhirFJVJGDDNgxeup7e6 HVVxQtkxslABlElQVoeaJ1axZjXe/0P/VA9WuMgcEdzcWAkcSmy4OFclaKppnT6Ai+CT YVbBl66fxFfNzgLvWFVTaGDa32TvibyRjWcgAK7xh5hWThS5AFcwo53DS0PmFOExlBUJ Hclw== 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=mmF7e6PV4DQ6WxG/w3b3vqgg+yxdUbWdT8nfYyPv+5DGypbsOTdvm5Yp/oH9V63H2u zO+rCvdOCL38hauR0uZHPUO33iJUhjUP+g8UqS8AhAe2dNNuiBelhLx6iAdpAluk11D/ mMF1wWvD7i3TBeNzdHLdlR5xRVTztbvC7DRsOOYG+ezf6jestHYyYA2tFp3IuTWa4TG8 j0V6AR9YcTqeQ5S/BlsfgueQOjrMQz0pgwIbtAwhF3aChWShpjXAKZbs4Mdmw3yelRsX J6DHiXzg754KUOtI7hnS5UUXsHwdIGfdcZSnznhhYckXFtAdJzRVKx0bgcrTKx3z4NWy LsgA== X-Gm-Message-State: AOAM532d+Xs3uSw+8lhsbr7kw+5BpfxyZ3DfnnzXVT8MMdlJiY+egJmU kG0HnUmw+SugwL2PJGe6gwmiEeyTFP+4qIX3ceAncTeGhOGN64zUhvQDJRPMhuKsRXiariWFzNb jBg9BJyAAYLlTjwQS6MG3Arm8Ncg4mRWbcuXO60eVvHu3Q18BuDoerMrdm81aDO8= X-Google-Smtp-Source: ABdhPJxKXRDMn4Swgqsq5vJ++TLfR8yTk5ESZ6D3Nee36eQ5/bT/AD1pIEtCXDfHqc3vQ2hiyXTwFrwdGi08yw== 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:e4c5:: with SMTP id b188mr3649502wmh.78.1610466183095; Tue, 12 Jan 2021 07:43:03 -0800 (PST) Date: Tue, 12 Jan 2021 15:42:35 +0000 In-Reply-To: <20210112154235.2192781-1-jackmanb@google.com> Message-Id: <20210112154235.2192781-12-jackmanb@google.com> Mime-Version: 1.0 References: <20210112154235.2192781-1-jackmanb@google.com> X-Mailer: git-send-email 2.30.0.284.gd98b1dd5eaa7-goog Subject: [PATCH bpf-next v6 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.