linux-kernel - Re: [PATCH] ARM: fix alignement of __bug

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Date:	Sun, 06 Sep 2015 00:12:59 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Dave Martin <Dave.Martin@....com>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: fix alignement of __bug_table section entries

Russell King - ARM Linux <linux@....linux.org.uk> writes:

>> Moreover, this is consistent with the fact that this commit is in linux-next but
>> not in v4.1 :
>>     a5e090acbf54 ("ARM: software-based priviledged-no-access support")
>> 
>> So the issue is around this SW_DOMAIN_PAN, at least on PXA.
>
> Is it only PXA which seems to be affected?
Sorry I don't know, I only own pxa platforms.

> If so, you may need to add:
>
> 	mrc p15, 0, \rd, c2, c0, 0
> 	mov \rd, \rd
> 	sub pc, pc, #4
>
> to the places we update the domain access register to ensure that the
> Xscale pipeline stalls to allow the CP15 DACR update to hit.
Okay, I'll try that.

By the way, the ARMv5 manual states in chapter "B4.5.1 MMU Fault" that for a
DACR update, a "PrefetchFlush" operation has to be done (chapter B2.6.3
PrefetchFlush CP15 register 7), quoting :
    Changes to the Domain Access Control register are synchronized by performing
    a PrefetchFlush operation (or as result of an exception or exception
    return). See Changes to CP15 registers and the memory order model on page
    B2-24 for details.

Cheers.

-- 
Robert
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