linux-kernel - RE: framebuffer corruption due to overlapping stp instructions on arm64

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Date:   Wed, 8 Aug 2018 14:26:11 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Mikulas Patocka' <mpatocka@...hat.com>
CC:     'Catalin Marinas' <catalin.marinas@....com>,
        Matt Sealey <neko@...uhatsu.net>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        "Jingoo Han" <jingoohan1@...il.com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: RE: framebuffer corruption due to overlapping stp instructions on
 arm64

From: Mikulas Patocka
> Sent: 08 August 2018 14:47
...
> The problem on ARM is that I see data corruption when the overlapping
> unaligned writes are done just by a single core.

Is this a sequence of unaligned writes (that shouldn't modify the
same physical locations) or an aligned write followed by an
unaligned one that updates part of the earlier write.
(Or the opposite order?)

It might be that the unaligned writes are bypassing the write-combining
buffer (without flushing it) - so overtake the aligned write.

Alternatively the unaligned writes go through the write-combining
buffer but the byte-enables aren't handled in the expected way.

It ought to be possible to work out which sequence is actually broken.

	David

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