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From: Mark Salter <msalter@redhat.com>
To: Max Filippov <jcmvbkbc@gmail.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>,
	Rob Herring <robh@kernel.org>, Kees Cook <keescook@chromium.org>,
	LKML <linux-kernel@vger.kernel.org>, Liu hua <sdu.liu@huawei.com>,
	Rabin Vincent <rabin@rab.in>,
	Nikolay Borisov <Nikolay.Borisov@arm.com>,
	Leif Lindholm <leif.lindholm@linaro.org>,
	Tomasz Figa <t.figa@samsung.com>,
	Doug Anderson <dianders@google.com>,
	Will Deacon <will.deacon@arm.com>,
	Laura Abbott <lauraa@codeaurora.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Russell King - ARM Linux <linux@arm.linux.org.uk>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/7] arm: use generic fixmap.h
Date: Thu, 07 Aug 2014 13:23:14 -0400	[thread overview]
Message-ID: <1407432194.599.13.camel@deneb.redhat.com> (raw)
In-Reply-To: <CAMo8Bf+DP-xZGnnFFvwc1XDEGUGkj1KkYQ_x+2i_hE0a9t7NKw@mail.gmail.com>

On Thu, 2014-08-07 at 19:42 +0400, Max Filippov wrote:
> On Thu, Aug 7, 2014 at 7:32 PM, Nicolas Pitre <nicolas.pitre@linaro.org> wrote:
> > On Thu, 7 Aug 2014, Rob Herring wrote:
> >
> >> 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.
> >
> > Why not switching everybody to positive offsets then?
> 
> I can cook a patch if people agree that that'd be good.
> 

I think that would be fine. I think x86 was first and used a negative
negative offset. Others that followed just copied that. When I did the
generic fixmap patch, using a negative offset was the natural thing to
do. Arm was only arch doing it differently.



WARNING: multiple messages have this Message-ID (diff)
From: msalter@redhat.com (Mark Salter)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 1/7] arm: use generic fixmap.h
Date: Thu, 07 Aug 2014 13:23:14 -0400	[thread overview]
Message-ID: <1407432194.599.13.camel@deneb.redhat.com> (raw)
In-Reply-To: <CAMo8Bf+DP-xZGnnFFvwc1XDEGUGkj1KkYQ_x+2i_hE0a9t7NKw@mail.gmail.com>

On Thu, 2014-08-07 at 19:42 +0400, Max Filippov wrote:
> On Thu, Aug 7, 2014 at 7:32 PM, Nicolas Pitre <nicolas.pitre@linaro.org> wrote:
> > On Thu, 7 Aug 2014, Rob Herring wrote:
> >
> >> 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.
> >
> > Why not switching everybody to positive offsets then?
> 
> I can cook a patch if people agree that that'd be good.
> 

I think that would be fine. I think x86 was first and used a negative
negative offset. Others that followed just copied that. When I did the
generic fixmap patch, using a negative offset was the natural thing to
do. Arm was only arch doing it differently.

  reply	other threads:[~2014-08-07 17:24 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-08-06 19:32 [PATCH 0/7] arm: support CONFIG_RODATA Kees Cook
2014-08-06 19:32 ` Kees Cook
2014-08-06 19:32 ` [PATCH 1/7] arm: use generic fixmap.h Kees Cook
2014-08-06 19:32   ` Kees Cook
2014-08-07  2:24   ` Laura Abbott
2014-08-07  2:24     ` Laura Abbott
2014-08-07 14:35     ` Kees Cook
2014-08-07 14:35       ` Kees Cook
2014-08-07 15:15   ` Max Filippov
2014-08-07 15:15     ` Max Filippov
2014-08-07 15:22     ` Rob Herring
2014-08-07 15:22       ` Rob Herring
2014-08-07 15:32       ` Nicolas Pitre
2014-08-07 15:32         ` Nicolas Pitre
2014-08-07 15:42         ` Max Filippov
2014-08-07 15:42           ` Max Filippov
2014-08-07 17:23           ` Mark Salter [this message]
2014-08-07 17:23             ` Mark Salter
2014-08-06 19:32 ` [PATCH 2/7] arm: fixmap: implement __set_fixmap() Kees Cook
2014-08-06 19:32   ` Kees Cook
2014-08-06 19:32 ` [PATCH 3/7] arm: mm: reduce fixmap kmap from 32 to 16 CPUS Kees Cook
2014-08-06 19:32   ` Kees Cook
2014-08-06 19:32 ` [PATCH 4/7] arm: use fixmap for text patching when text is RO Kees Cook
2014-08-06 19:32   ` Kees Cook
2014-08-06 19:32 ` [PATCH 5/7] ARM: kexec: Make .text R/W in machine_kexec Kees Cook
2014-08-06 19:32   ` Kees Cook
2014-08-06 19:32 ` [PATCH 6/7] ARM: mm: allow non-text sections to be non-executable Kees Cook
2014-08-06 19:32   ` Kees Cook
2014-08-06 19:32 ` [PATCH 7/7] ARM: mm: allow text and rodata sections to be read-only Kees Cook
2014-08-06 19:32   ` Kees Cook

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