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

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Message-ID: <20180805215150.GB1862@amd>
Date:   Sun, 5 Aug 2018 23:51:50 +0200
From:   Pavel Machek <pavel@....cz>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Andrew Pinski <pinskia@...il.com>,
        Richard Earnshaw <Richard.Earnshaw@....com>,
        ard.biesheuvel@...aro.org,
        Ramana Radhakrishnan <ramana.gcc@...glemail.com>,
        Florian Weimer <fweimer@...hat.com>,
        thomas.petazzoni@...e-electrons.com,
        GNU C Library <libc-alpha@...rceware.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, linux@...linux.org.uk,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: framebuffer corruption due to overlapping stp instructions on
 arm64

Hi!

> > Can you run the test program on x86 using the similar framebuffer
> > setup?  Does doing two writes (one aligned and one unaligned but
> > overlapping with previous one) cause the same issue?  I suspect it
> > does, then using memcpy for frame buffers is wrong.

I'm pretty sure it will work ok on x86.

> Overlapping unaligned writes work on x86 - they have to, because of 
> backward compatibility.

It is not that easy. 8086s (and similar) did not have MTRRs and PATs
either. Overlapping unaligned writes _on main memory_, _with normal
MTRR settings_ certainly work ok on x86.

Chances is memory type can be configured to work similar way on your
ARM/PCIe case?

> 8086, 80286 and 80386 didn't have any cache at all.

386s had cache (but not on die).
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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