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From:   Yuri Norov <ynorov@marvell.com>
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Yury Norov <yury.norov@gmail.com>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Arnd Bergmann <arnd@arndb.de>,
        Kees Cook <keescook@chromium.org>,
        Matthew Wilcox <willy@infradead.org>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Mike Travis <travis@sgi.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 3/6] bitmap_parselist: rework input string parser
Thread-Topic: [PATCH 3/6] bitmap_parselist: rework input string parser
Thread-Index: AQHU5BgtSKN9Jh48vk6eUkQSxrS94Q==
Date:   Tue, 26 Mar 2019 21:09:18 +0000
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+ Mike Travis <travis@sgi.com>=0A=
+ Thomas Gleixner <tglx@linutronix.de>=0A=
=0A=
----------------------------------------------------------------------=0A=
On Tue, Mar 26, 2019 at 12:07:45AM +0300, Yury Norov wrote:=0A=
>> The requirement for this rework is to keep the __bitmap_parselist()=0A=
>> copy-less and single-pass but make it more readable and maintainable by=
=0A=
>> splitting into logical parts and removing explicit nested cycles and=0A=
>> opaque local variables.=0A=
>>=0A=
>> __bitmap_parselist() can parse userspace inputs and therefore we cannot=
=0A=
>> use simple_strtoul() to parse numbers.=0A=
=0A=
> So, all above depends to what memory we access kernel / user space.=0A=
> Perhaps we can get copy of memory of a given size and then parse it in ke=
rnel space always?=0A=
=0A=
> --=0A=
> With Best Regards,=0A=
> Andy Shevchenko=0A=
=0A=
What I missed during rework is that we have only one caller of *parselist_u=
ser=A0 -=0A=
it's write_irq_affinity() introduced by Mike Travis in kernel/irq/proc.c. I=
t doesn't look=0A=
like a hot path as it's file operations handler. If no objections from Mike=
 or Thomas,=0A=
I think it would make sense to copy_from_user() the userspace data at the b=
eginning=0A=
in sake of simplicity of __bitmap_parselist(), as you suggested above.=0A=
=0A=
Yury=0A=