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Re: framebuffer corruption due to overlapping stp instructions on arm64
- From: Catalin Marinas <catalin dot marinas at arm dot com>
- To: Mikulas Patocka <mpatocka at redhat dot com>
- Cc: Thomas Petazzoni <thomas dot petazzoni at free-electrons dot com>, Joao Pinto <Joao dot Pinto at synopsys dot com>, libc-alpha at sourceware dot org, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Jingoo Han <jingoohan1 at gmail dot com>, Will Deacon <will dot deacon at arm dot com>, Russell King <linux at armlinux dot org dot uk>, Linux Kernel Mailing List <linux-kernel at vger dot kernel dot org>, Matt Sealey <neko at bakuhatsu dot net>, linux-pci at vger dot kernel dot org, linux-arm-kernel <linux-arm-kernel at lists dot infradead dot org>
- Date: Wed, 8 Aug 2018 15:28:53 +0100
- Subject: Re: framebuffer corruption due to overlapping stp instructions on arm64
- References: <alpine.LRH.2.02.1808021242320.31834@file01.intranet.prod.int.rdu2.redhat.com> <CAHCPf3tFGqkYEcWNN4LaWThw_rVqT316pzLv6T7RfxwO-eZ0EA@mail.gmail.com> <alpine.LRH.2.02.1808030212340.17672@file01.intranet.prod.int.rdu2.redhat.com> <CAKv+Gu8DeuksZhk1g3q_msSKV_hSY_2e1uzVten9-oGO3j9Sqg@mail.gmail.com> <20180803094129.GB17798@arm.com> <alpine.LRH.2.02.1808031235410.31584@file01.intranet.prod.int.rdu2.redhat.com> <20180808113927.GA24736@iMac.local> <alpine.LRH.2.02.1808081011110.9997@file01.intranet.prod.int.rdu2.redhat.com>
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