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.
next prev parent reply other threads:[~2014-08-07 17:24 UTC|newest]
Thread overview: 15+ 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 ` [PATCH 1/7] arm: use generic fixmap.h Kees Cook
2014-08-07 2:24 ` Laura Abbott
2014-08-07 14:35 ` Kees Cook
2014-08-07 15:15 ` Max Filippov
2014-08-07 15:22 ` Rob Herring
2014-08-07 15:32 ` Nicolas Pitre
2014-08-07 15:42 ` Max Filippov
2014-08-07 17:23 ` Mark Salter [this message]
2014-08-06 19:32 ` [PATCH 2/7] arm: fixmap: implement __set_fixmap() 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 ` [PATCH 4/7] arm: use fixmap for text patching when text is RO 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 ` [PATCH 6/7] ARM: mm: allow non-text sections to be non-executable Kees Cook
2014-08-06 19:32 ` [PATCH 7/7] ARM: mm: allow text and rodata sections to be read-only Kees Cook
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