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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 8E09AC28CF6 for ; Sat, 4 Aug 2018 00:58:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3757420895 for ; Sat, 4 Aug 2018 00:58:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3757420895 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732229AbeHDC47 (ORCPT ); Fri, 3 Aug 2018 22:56:59 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:34994 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1731959AbeHDC47 (ORCPT ); Fri, 3 Aug 2018 22:56:59 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 291F24067720; Sat, 4 Aug 2018 00:58:20 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (file01.intranet.prod.int.rdu2.redhat.com [10.11.5.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B8BC81DB47; Sat, 4 Aug 2018 00:58:19 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (localhost [127.0.0.1]) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4) with ESMTP id w740wJEA026593; Fri, 3 Aug 2018 20:58:19 -0400 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id w740wI0n026589; Fri, 3 Aug 2018 20:58:18 -0400 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Fri, 3 Aug 2018 20:58:18 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: "Richard Earnshaw (lists)" cc: Ard Biesheuvel , Ramana Radhakrishnan , Florian Weimer , Thomas Petazzoni , GNU C Library , Andrew Pinski , Catalin Marinas , Will Deacon , Russell King , LKML , linux-arm-kernel Subject: Re: framebuffer corruption due to overlapping stp instructions on arm64 In-Reply-To: <11f9185a-7f71-83df-3a57-0a0ae9c1f934@arm.com> Message-ID: References: <9acdacdb-3bd5-b71a-3003-e48132ee1371@redhat.com> <11f9185a-7f71-83df-3a57-0a0ae9c1f934@arm.com> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.7]); Sat, 04 Aug 2018 00:58:20 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.7]); Sat, 04 Aug 2018 00:58:20 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'mpatocka@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 3 Aug 2018, Richard Earnshaw (lists) wrote: > Whoa, hold on. > > Memcpy should never be used on device memory. Period. Memcpy doesn't > know anything about what size of access is needed for accessing a device. > > But why is the buffer in device memory rather than some other form of > uncached memory? > > If you change memcpy to deal with an aspect of the system hardware, > you'll end up hosing performance EVERYWHERE. DON'T DO IT! memcpy in glibc uses ifunc selection and it already has optimized variants for Falkor and Thunder-X. You can add just another variant for Armada-8040 that works around this bug and you won't be harming anyone but users of Armada-8040. Furthermore, you can detect in the kernel that the PCI bus has some device with prefetchable BAR and activate the workaround only if there is videocard plugged in the PCIe slot. > If you must, create a new API with tighter semantics, but don't change > memcpy to accommodate this. > > Anyway, back to the original report. What memory mapping is being used? > In detail? It is PCI prefetchable BAR. It is mapped using pgprot_writecombine, which results in MT_NORMAL_NC page attributes. (the MT_DEVICE_nGnRE can't be used because it results in crashes due to unaligned accesses to videoram). > R. Mikulas