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

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Message-ID: <alpine.LRH.2.02.1808071010240.11209@file01.intranet.prod.int.rdu2.redhat.com>
Date:   Tue, 7 Aug 2018 10:14:13 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
cc:     Florian Weimer <fweimer@...hat.com>,
        Andrew Pinski <pinskia@...il.com>,
        Richard Earnshaw <Richard.Earnshaw@....com>,
        Ramana Radhakrishnan <ramana.gcc@...glemail.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        GNU C Library <libc-alpha@...rceware.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        LKML <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



On Mon, 6 Aug 2018, Ard Biesheuvel wrote:

> No that works fine for me. VDPAU acceleration works as well, but it
> depends on your chromium build whether it can actually use it, I
> think? In any case, mplayer can use vdpau to play 1080p h264 without
> breaking a sweat on this system.
> 
> Note that the VDPAU driver also relies on memory semantics, i.e., it
> may use DC ZVA (zero cacheline) instructions which are not permitted
> on device mappings. This is probably just glibc's memset() being
> invoked, but I remember hitting this on another PCIe-impaired arm64
> system with Synopsys PCIe IP

DC ZVA can be disabled with the SCTRL_EL1.DZE bit, so that neither kernel 
nor userspace will use it. If the mapping didn't support unaligned writes, 
it would be worse.

Mikulas