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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 BDD19C4338F for ; Tue, 17 Aug 2021 13:27:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9B4D660F39 for ; Tue, 17 Aug 2021 13:27:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239706AbhHQN2L (ORCPT ); Tue, 17 Aug 2021 09:28:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41962 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236398AbhHQN2J (ORCPT ); Tue, 17 Aug 2021 09:28:09 -0400 Received: from mail-ot1-x330.google.com (mail-ot1-x330.google.com [IPv6:2607:f8b0:4864:20::330]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4439BC061764 for ; Tue, 17 Aug 2021 06:27:36 -0700 (PDT) Received: by mail-ot1-x330.google.com with SMTP id h63-20020a9d14450000b02904ce97efee36so24911726oth.7 for ; Tue, 17 Aug 2021 06:27:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=zWHDjIJawTHtbmwaJcKwdk8W++TJIaWlzkrKoGu1IaU=; b=dg9OG94AdzJ4ptbnkm6zajAKdgcwQc2B/9ce5oIk4e+K8FFePWxsBRUsqCRBg9ObwY 8eEBGk31gtAelYKTmqn7zwdMLiPyFJlTIEWhicjSVfQPCJ1vujuAckMuR9ySstax8RmT 29499/yQ/kxDGEsOii0jh5PqYOf2tuA6HMva16Uc1LMweHD1+zN4U5sZo/6ftqFpx4Mf 64HpgzLfqpZQtKnwLUJ5BfPSF+jDLsiXO9iB2gr0FVUMk/PqYKcc8c6manWMdq+7mTap LAVNHWRoKN55cZ5ZZM4qUfh/h5Y6SM/QbYPnOf26JQJwxYOmYQ+3LN5k2d4ljEKVjTOu fVCg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=zWHDjIJawTHtbmwaJcKwdk8W++TJIaWlzkrKoGu1IaU=; b=jIIEIwvskjE/0k+wIXq/lwSQ17IPmi7xeDpCD2Ay+n7bsRhox2qnvt8BOoUFcnkH9N wT6tn14wyXAh0KZ4tGCiGGEmk36kPObQKygwaNTc+9Xzu9Sfgx/cwZvaO2jmBIp4SPD+ 1fR45U4I4dqjCc61U548LMDTn1fdhbeg/940z8Tgl32F0k1+duaTRL2rC7C74N80OAhb 2ZSCNni0SGmXJz2J3XSonm1C8OmDDG+bxSqHJC+lh0IdRaM9xSLmh6dkNq4GaCNNHR2E dyg3gEmG30mymKzMSenB+DOc1WLLAqU3OV4agrM3XRmnj/ewwjf5eLkjC1KqJ1hRUWJP v5pA== X-Gm-Message-State: AOAM530RmERgaMeyHmWr3LJTQnfIw4E7gHuazOzs/WRMdVu64eDGhIuD rW/ACfaaXQ5pHFfdt5zJUHiv7iJMnuCBT8uHJPQFNA== X-Google-Smtp-Source: ABdhPJzz5g18ioI6eWHzPZd89cVcbC2pdeXSEWQCiJC21pT2iy9zZifvMdhmcEKvVH0zmPV5E982UyIcLPqeIs00+Ag= X-Received: by 2002:a9d:d04:: with SMTP id 4mr2775588oti.251.1629206855297; Tue, 17 Aug 2021 06:27:35 -0700 (PDT) MIME-Version: 1.0 References: <20210816145945.GB121345@rowland.harvard.edu> <20210816192109.GC121345@rowland.harvard.edu> <20210816205057.GN4126399@paulmck-ThinkPad-P17-Gen-1> <20210817122816.GA12746@willie-the-truck> In-Reply-To: <20210817122816.GA12746@willie-the-truck> From: Marco Elver Date: Tue, 17 Aug 2021 15:27:23 +0200 Message-ID: Subject: Re: LKMM: Read dependencies of writes ordered by dma_wmb()? To: Will Deacon Cc: "Paul E. McKenney" , Alan Stern , Boqun Feng , Andrea Parri , Mark Rutland , Dmitry Vyukov , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 17 Aug 2021 at 14:28, Will Deacon wrote: > Just on this bit... > > On Mon, Aug 16, 2021 at 01:50:57PM -0700, Paul E. McKenney wrote: > > 5. The dma_mb(), dma_rmb(), and dma_wmb() appear to be specific > > to ARMv8. > > These are useful on other architectures too! IIRC, they were added by x86 in > the first place. They're designed to be used with dma_alloc_coherent() > allocations where you're sharing something like a ring buffer with a device > and they guarantee accesses won't be reordered before they become visible > to the device. They _also_ provide the same ordering to other CPUs. Ah, good you pointed it out again. Re-reading memory-barriers.txt and it does also say these provide order for other CPUs... > I gave a talk at LPC about some of this, which might help (or might make > things worse...): > > https://www.youtube.com/watch?v=i6DayghhA8Q Nice, thank you! > Ignore the bits about mmiowb() as we got rid of that. > > Will