From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Date: Wed, 8 Aug 2018 16:14:45 +0100 From: Catalin Marinas To: "Richard Earnshaw (lists)" Subject: Re: framebuffer corruption due to overlapping stp instructions on arm64 Message-ID: <20180808151444.GF24736@iMac.local> References: <20180803094129.GB17798@arm.com> <20180808113927.GA24736@iMac.local> MIME-Version: 1.0 In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Thomas Petazzoni , Joao Pinto , libc-alpha@sourceware.org, Ard Biesheuvel , Jingoo Han , Will Deacon , Russell King , Linux Kernel Mailing List , Mikulas Patocka , Matt Sealey , linux-pci@vger.kernel.org, linux-arm-kernel Content-Type: text/plain; charset="us-ascii" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+bjorn=helgaas.com@lists.infradead.org List-ID: On Wed, Aug 08, 2018 at 04:01:12PM +0100, Richard Earnshaw wrote: > On 08/08/18 15:12, 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. > > I don't think you've told us what form the corruption takes. Does it > lose some bytes? Modify values beyond the copy range? Write completely > arbitrary values? >>From this message: https://lore.kernel.org/lkml/alpine.LRH.2.02.1808060553130.30832@file01.intranet.prod.int.rdu2.redhat.com/ - failing to write a few bytes - writing a few bytes that were written 16 bytes before - writing a few bytes that were written 16 bytes after > The overlapping writes in memcpy never write different values to the > same location, so I still feel this must be some sort of HW issue, not a > SW one. So do I (my interpretation is that it combines or rather skips some of the writes to the same 16-byte address as it ignores the data strobes). -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel