linux-kernel - Re: [PATCH 1/7] arm: use generic fixmap.h

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Date:	Thu, 7 Aug 2014 10:22:28 -0500
From:	Rob Herring <robh@...nel.org>
To:	Max Filippov <jcmvbkbc@...il.com>
Cc:	Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mark Salter <msalter@...hat.com>, Liu hua <sdu.liu@...wei.com>,
	Rabin Vincent <rabin@....in>,
	Nikolay Borisov <Nikolay.Borisov@....com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Tomasz Figa <t.figa@...sung.com>,
	Doug Anderson <dianders@...gle.com>,
	Will Deacon <will.deacon@....com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/7] arm: use generic fixmap.h

On Thu, Aug 7, 2014 at 10:15 AM, Max Filippov <jcmvbkbc@...il.com> wrote:
> Hi,
>
> On Wed, Aug 6, 2014 at 11:32 PM, Kees Cook <keescook@...omium.org> wrote:
>> ARM is different from other architectures in that fixmap pages are indexed
>> with a positive offset from FIXADDR_START.  Other architectures index with
>> a negative offset from FIXADDR_TOP.  In order to use the generic fixmap.h
>
> Does anybody know if there's any reason why generic fixmap.h uses negative
> offsets? It complicates things with no obvious benefit if you e.g. try to align
> virtual address in the fixmap region with physical page color (that's why I've
> switched xtensa to positive fixmap addressing in v3.17).

No, but each arch doing it differently is even more annoying.

Rob
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