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From: Rob Herring <robh@kernel.org>
Date: Thu, 7 Aug 2014 10:22:28 -0500
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Subject: Re: [PATCH 1/7] arm: use generic fixmap.h
To: Max Filippov <jcmvbkbc@gmail.com>
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On Thu, Aug 7, 2014 at 10:15 AM, Max Filippov <jcmvbkbc@gmail.com> wrote:
> Hi,
>
> On Wed, Aug 6, 2014 at 11:32 PM, Kees Cook <keescook@chromium.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

From mboxrd@z Thu Jan  1 00:00:00 1970
From: robh@kernel.org (Rob Herring)
Date: Thu, 7 Aug 2014 10:22:28 -0500
Subject: [PATCH 1/7] arm: use generic fixmap.h
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 <1407353564-21478-2-git-send-email-keescook@chromium.org>
 <CAMo8Bf+uq1vhqb7KxnNFHTZ53C1mtw_Do6dn09j7jjw_7MWF_Q@mail.gmail.com>
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To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Aug 7, 2014 at 10:15 AM, Max Filippov <jcmvbkbc@gmail.com> wrote:
> Hi,
>
> On Wed, Aug 6, 2014 at 11:32 PM, Kees Cook <keescook@chromium.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