From patchwork Mon Dec 7 16:07:34 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Brendan Jackman X-Patchwork-Id: 11956281 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=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 F3719C2D0E4 for ; Mon, 7 Dec 2020 16:09:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CFB8923741 for ; Mon, 7 Dec 2020 16:09:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727713AbgLGQJw (ORCPT ); Mon, 7 Dec 2020 11:09:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55768 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727687AbgLGQJv (ORCPT ); Mon, 7 Dec 2020 11:09:51 -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 CBCA7C0619DA for ; Mon, 7 Dec 2020 08:08:37 -0800 (PST) Received: by mail-wm1-x34a.google.com with SMTP id k23so5518475wmj.1 for ; Mon, 07 Dec 2020 08:08:37 -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=/lv6DrUY5wlxHYDqv4wuxYv1KAcmfbWk3hb5TBKA9OQ=; b=qrAzvndx/RfGimRH9rKkjCXl5R5vcp0lJ2luB3NAF1M0qm2i6C92p+0/ZdytUErKZ4 AeQ4lopdDG6WorylJp4LWT5Rv9Lz4cpcHvwZ6WsMtTB49032zXcDT2WI5pFmckzGKUPq 2AyIjpbjtG/r6lmJvHb4oQL5MWxVTTAXq+eKY8OiepizFdmsojaPbdkvZLDYTPfujo/e CgN4INGp/TCJVRnSDwgoH6Tfz6bX1O+6qTfyNwp0CG2G5KX+Sk6786JDajTfaLUBKzRb yPrL8w3uDWn/sNQ9MzknDV517kpssAZOCpY4HzttuLEsXHcgyEzzvjuqkdfMDnVP197o ffGw== 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=/lv6DrUY5wlxHYDqv4wuxYv1KAcmfbWk3hb5TBKA9OQ=; b=ibsQT5ElcQ9M5iScz2tGDiqiMb1BwVY9XUn7H1sd5qPnFZ+XbUkEsoiJA9A3IKwPyM 2z9l3KohNpo5U3aVAdFwzgnLNjtAmompximKiZT82uxlMYcGxTinHfIcwVJgfSLjcXVc HVoHeszgXksBWrYhG2phg+/llUpzaDLZf6Yu6rlu6ytydyZjvIiD0ICYoEZYkEmRjNdI iO6UY1lxUMtzGZwDODj6vPRn8GA66pmgyMm1k42rplkkxvAGn+LJrIgHwgOqb5Ugtk2B Xjj3a7QXRBuSyhBglqiou6DosRQlQBaKDu89qVPN0mXi+ALZzaBxAVLLibjlnv31EbjD EJ1A== X-Gm-Message-State: AOAM532ouSYoYKk33rUVk8LMVq84m9S6WD7Cogb0zgCHv0+jcHLO1ZAh gRaWWKi9rsJ/VerSzTFABedrJVcx/WWAxw7pu/vJ82humTH01PFAruPAi2s8S+UKYzVfFptbCyL 2mb7C1ujP5XEm6eP9I0pmC7zwSyRHB8gnrQPoqIcdupKrDDBrx0lPgBDU38zdhEc= X-Google-Smtp-Source: ABdhPJxzkxIq0ByuLG8V4MG6Y6ki3FwPpCc3rrTeLj6hrKEf2B7w308rHmXjLVsALm2O3c/Kego1U7170Hty2w== 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:5585:: with SMTP id j127mr19812912wmb.169.1607357316448; Mon, 07 Dec 2020 08:08:36 -0800 (PST) Date: Mon, 7 Dec 2020 16:07:34 +0000 In-Reply-To: <20201207160734.2345502-1-jackmanb@google.com> Message-Id: <20201207160734.2345502-12-jackmanb@google.com> Mime-Version: 1.0 References: <20201207160734.2345502-1-jackmanb@google.com> X-Mailer: git-send-email 2.29.2.576.ga3fc446d84-goog Subject: [PATCH bpf-next v4 11/11] 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 Document new atomic instructions. Signed-off-by: Brendan Jackman Acked-by: Yonghong Song --- 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