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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 7877CC433E0 for ; Tue, 26 May 2020 13:07:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 53E2220899 for ; Tue, 26 May 2020 13:07:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728965AbgEZNHP (ORCPT ); Tue, 26 May 2020 09:07:15 -0400 Received: from elvis.franken.de ([193.175.24.41]:39889 "EHLO elvis.franken.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726437AbgEZNHP (ORCPT ); Tue, 26 May 2020 09:07:15 -0400 Received: from uucp (helo=alpha) by elvis.franken.de with local-bsmtp (Exim 3.36 #1) id 1jdZIW-00088o-00; Tue, 26 May 2020 15:07:12 +0200 Received: by alpha.franken.de (Postfix, from userid 1000) id 76711C0274; Tue, 26 May 2020 15:01:28 +0200 (CEST) Date: Tue, 26 May 2020 15:01:28 +0200 From: Thomas Bogendoerfer To: Lichao Liu Cc: Jiaxun Yang , Paul Burton , Robin Murphy , Geert Uytterhoeven , Max Filippov , yuanjunqing@loongson.cn, linux-mips@vger.kernel.org Subject: Re: [PATCH] MIPS: CPU_LOONGSON2EF need software to maintain cache consistency Message-ID: <20200526130128.GA8487@alpha.franken.de> References: <20200526111438.3788-1-liulichao@loongson.cn> <20200526193859.0adaea3b@halation.net.flygoat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Tue, May 26, 2020 at 08:40:28PM +0800, Lichao Liu wrote: > Loongson-2EF need software maintain cache consistency, So when using > streaming DMA, software needs to maintain consistency. > > dma_map_single() is correct, but dma_unmap_single is wrong. > > The function call path: > 'dma_unmap_single->dma_unmap_page_attrs->dma_direct_unmap_page-> > dma_direct_sync_single_for_cpu->arch_sync_dma_for_cpu-> > cpu_needs_post_dma_flush' > > In current version, 'cpu_needs_post_dma_flush' will return false > at Loongon-2EF platform, and dma_unmap_single will not invalidate cache, > driver may access wrong dma data. why should it ? CPU must not touch data while it's mapped for DMA. > I don't know what's the exact meaning of "fill random cachelines with > stale data at any time". I always think 'cpu_needs_post_dma_flush()' > means whether this platform needs software to maintain cache consistency. this will only happen, if cpu speculates creates dirty cache lines by speculation as R10k type of CPUs do. > I found this problem in 4.19.90 kernel's ethernet driver, > and this patch can fix this problem. if CPU isn't affected by the R10k speculation problem, it sounds more like wrong usage of DMA api. Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]