From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Date: Wed, 8 Aug 2018 15:28:53 +0100 From: Catalin Marinas To: Mikulas Patocka 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 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 , 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 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel