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 909CDC46471 for ; Mon, 6 Aug 2018 12:42:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 49C9F21A0B for ; Mon, 6 Aug 2018 12:42:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 49C9F21A0B 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 S1730266AbeHFOvV (ORCPT ); Mon, 6 Aug 2018 10:51:21 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:38100 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726988AbeHFOvV (ORCPT ); Mon, 6 Aug 2018 10:51:21 -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 6852580D; Mon, 6 Aug 2018 05:42:24 -0700 (PDT) Received: from [10.4.12.131] (e110467-lin.emea.arm.com [10.4.12.131]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 751CD3F2EA; Mon, 6 Aug 2018 05:42:22 -0700 (PDT) Subject: Re: framebuffer corruption due to overlapping stp instructions on arm64 To: Mikulas Patocka , Ard Biesheuvel Cc: Thomas Petazzoni , Joao Pinto , linux-pci , Jingoo Han , Will Deacon , Russell King , Linux Kernel Mailing List , Matt Sealey , Catalin Marinas , linux-arm-kernel References: <20180803094129.GB17798@arm.com> From: Robin Murphy Message-ID: <99fff4fe-afa9-f12f-a518-472a9dd1c530@arm.com> Date: Mon, 6 Aug 2018 13:42:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/08/18 11:25, Mikulas Patocka wrote: [...] >> None of this explains why some transactions fail to make it across >> entirely. The overlapping writes in question write the same data to >> the memory locations that are covered by both, and so the ordering in >> which the transactions are received should not affect the outcome. > > You're right that the corruption couldn't be explained just by reordering > writes. My hypothesis is that the PCIe controller tries to disambiguate > the overlapping writes, but the disambiguation logic was not tested and it > is buggy. If there's a barrier between the overlapping writes, the PCIe > controller won't see any overlapping writes, so it won't trigger the > faulty disambiguation logic and it works. > > Could the ARM engineers look if there's some chicken bit in Cortex-A72 > that could insert barriers between non-cached writes automatically? I don't think there is, and even if there was I imagine it would have a pretty hideous effect on non-coherent DMA buffers and the various other places in which we have Normal-NC mappings of actual system RAM. > I observe these kinds of corruptions: > - failing to write a few bytes That could potentially be explained by the reordering/atomicity issues Matt mentioned, i.e. the load is observing part of the store, before the store has fully completed. > - writing a few bytes that were written 16 bytes before > - writing a few bytes that were written 16 bytes after Those sound more like the interconnect or root complex ignoring the byte strobes on an unaligned burst, of which I think the simplistic view would be "it's broken". FWIW I stuck my old Nvidia 7600GT card in my Arm Juno r2 board (2x Cortex-A72), built your test program natively with GCC 8.1.1 at -O2, and it's still happily flickering pixels in the corner of the console after nearly an hour (in parallel with some iperf3 just to ensure plenty of PCIe traffic). I would strongly suspect this issue is particular to Armada 8k, so its' probably one for the Marvell folks to take a closer look at - I believe some previous interconnect issues on those SoCs were actually fixable in firmware. Robin.