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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 B699DC4646D for ; Wed, 8 Aug 2018 14:29:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 615B8219E6 for ; Wed, 8 Aug 2018 14:29:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 615B8219E6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.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 S1727408AbeHHQsx (ORCPT ); Wed, 8 Aug 2018 12:48:53 -0400 Received: from foss.arm.com ([217.140.101.70]:39662 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727069AbeHHQsw (ORCPT ); Wed, 8 Aug 2018 12:48:52 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E188C7A9; Wed, 8 Aug 2018 07:28:57 -0700 (PDT) Received: from iMac.local (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CDB563F5D4; Wed, 8 Aug 2018 07:28:55 -0700 (PDT) Date: Wed, 8 Aug 2018 15:28:53 +0100 From: Catalin Marinas To: Mikulas Patocka Cc: Thomas Petazzoni , Joao Pinto , libc-alpha@sourceware.org, Ard Biesheuvel , Jingoo Han , Will Deacon , Russell King , Linux Kernel Mailing List , Matt Sealey , linux-pci@vger.kernel.org, linux-arm-kernel Subject: Re: framebuffer corruption due to overlapping stp instructions on arm64 Message-ID: <20180808142852.GD24736@iMac.local> References: <20180803094129.GB17798@arm.com> <20180808113927.GA24736@iMac.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 08, 2018 at 10:12:27AM -0400, Mikulas Patocka wrote: > On Wed, 8 Aug 2018, Catalin Marinas wrote: > > On Fri, Aug 03, 2018 at 01:09:02PM -0400, Mikulas Patocka wrote: > > > while (1) { > > > start = (unsigned)random() % (LEN + 1); > > > end = (unsigned)random() % (LEN + 1); > > > if (start > end) > > > continue; > > > for (i = start; i < end; i++) > > > data[i] = val++; > > > memcpy(map + start, data + start, end - start); > > > if (memcmp(map, data, LEN)) { > > > > It may be worth trying to do a memcmp(map+start, data+start, end-start) > > here to see whether the hazard logic fails when the writes are unaligned > > but the reads are not. > > > > This problem may as well appear if you do byte writes and read longs > > back (and I consider this a hardware problem on this specific board). > > I triad to insert usleep(10000) between the memcpy and memcmp, but the > same corruption occurs. So, it can't be read-after-write hazard. It is > caused by the improper handling of hazard between the overlapping writes > inside memcpy. It could get it wrong between subsequent writes to the same 64-bit range (e.g. the address & ~63 is the same but the data strobes for which bytes to write are different). If it somehow thinks that it's a write-after-write hazard even though the strobes are different, it could cancel one of the writes. It may be worth trying with a byte-only memcpy() function while keeping the default memcmp(). -- Catalin