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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 4DCBAC4360C for ; Tue, 2 Mar 2021 10:39:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 261F264F07 for ; Tue, 2 Mar 2021 10:39:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1578088AbhCBKfd (ORCPT ); Tue, 2 Mar 2021 05:35:33 -0500 Received: from mga11.intel.com ([192.55.52.93]:14012 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1838018AbhCBJRo (ORCPT ); Tue, 2 Mar 2021 04:17:44 -0500 IronPort-SDR: SWskgWMvj+YmA8TGkKwtfmd4krQsmTwrPtCn3hMaDjaf44hawMFFBYNSO/P1QDvl0s02xXL0ou bzQbj+UwKGNg== X-IronPort-AV: E=McAfee;i="6000,8403,9910"; a="183356978" X-IronPort-AV: E=Sophos;i="5.81,216,1610438400"; d="scan'208";a="183356978" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Mar 2021 01:17:01 -0800 IronPort-SDR: Bum09qkuPQg5WMxKjkqJJe/pqHMRPVGGG1Q17o2HOQU/Hwk239QOxFocuX+fIh4G/4Y+MFzQqV 5WmlFArNDznA== X-IronPort-AV: E=Sophos;i="5.81,216,1610438400"; d="scan'208";a="398777931" Received: from ilick-mobl1.ger.corp.intel.com (HELO btopel-mobl.ger.intel.com) ([10.249.41.237]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Mar 2021 01:16:57 -0800 Subject: Re: [PATCH bpf-next 2/2] libbpf, xsk: add libbpf_smp_store_release libbpf_smp_load_acquire To: Daniel Borkmann , =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , ast@kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Cc: magnus.karlsson@intel.com, jonathan.lemon@gmail.com, maximmi@nvidia.com, andrii@kernel.org, will@kernel.org References: <20210301104318.263262-1-bjorn.topel@gmail.com> <20210301104318.263262-3-bjorn.topel@gmail.com> <87k0qqx3be.fsf@toke.dk> <12f8969b-6780-f35f-62cd-ed67b1d8181a@iogearbox.net> From: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= Message-ID: <0121ca03-d806-8e50-aaac-0f97795d0fbe@intel.com> Date: Tue, 2 Mar 2021 10:16:52 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <12f8969b-6780-f35f-62cd-ed67b1d8181a@iogearbox.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 2021-03-02 10:13, Daniel Borkmann wrote: > On 3/2/21 9:05 AM, Björn Töpel wrote: >> On 2021-03-01 17:10, Toke Høiland-Jørgensen wrote: >>> Björn Töpel writes: >>>> From: Björn Töpel >>>> >>>> Now that the AF_XDP rings have load-acquire/store-release semantics, >>>> move libbpf to that as well. >>>> >>>> The library-internal libbpf_smp_{load_acquire,store_release} are only >>>> valid for 32-bit words on ARM64. >>>> >>>> Also, remove the barriers that are no longer in use. >>> >>> So what happens if an updated libbpf is paired with an older kernel (or >>> vice versa)? >> >> "This is fine." ;-) This was briefly discussed in [1], outlined by the >> previous commit! >> >> ...even on POWER. > > Could you put a summary or quote of that discussion on 'why it is okay > and does not > cause /forward or backward/ compat issues with user space' directly into > patch 1's > commit message? > > I feel just referring to a link is probably less suitable in this case > as it should > rather be part of the commit message that contains the justification on > why it is > waterproof - at least it feels that specific area may be a bit > under-documented, so > having it as direct part certainly doesn't hurt. > I agree; It's enough in the weed as it is already. I wonder if it's possible to cook a LKMM litmus test for this...? > Would also be great to get Will's ACK on that when you have a v2. :) > Yup! :-) Björn > Thanks, > Daniel > >> [1] https://lore.kernel.org/bpf/20200316184423.GA14143@willie-the-truck/