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Subject: Re: [PATCH 3/6] bitmap_parselist: rework input string parser
To:     Yuri Norov <ynorov@marvell.com>,
        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>
References: <20190325210748.6571-1-ynorov@marvell.com>
 <20190325210748.6571-4-ynorov@marvell.com>
 <20190326101045.GT9224@smile.fi.intel.com>
 <MN2PR18MB30862D49744CFC6FEAD78177CB5F0@MN2PR18MB3086.namprd18.prod.outlook.com>
From:   Mike Travis <mike.travis@hpe.com>
Message-ID: <ae8abbbe-108d-93bd-99d6-251e0d1f36ac@hpe.com>
Date:   Tue, 26 Mar 2019 14:58:45 -0700
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On 3/26/2019 2:09 PM, Yuri Norov wrote:
> + Mike Travis <travis@sgi.com>
> + Thomas Gleixner <tglx@linutronix.de>
> 
> ----------------------------------------------------------------------
> On Tue, Mar 26, 2019 at 12:07:45AM +0300, Yury Norov wrote:
>>> The requirement for this rework is to keep the __bitmap_parselist()
>>> copy-less and single-pass but make it more readable and maintainable by
>>> splitting into logical parts and removing explicit nested cycles and
>>> opaque local variables.
>>>
>>> __bitmap_parselist() can parse userspace inputs and therefore we cannot
>>> use simple_strtoul() to parse numbers.
> 
>> So, all above depends to what memory we access kernel / user space.
>> Perhaps we can get copy of memory of a given size and then parse it in kernel space always?
> 
>> --
>> With Best Regards,
>> Andy Shevchenko
> 
> What I missed during rework is that we have only one caller of *parselist_user? -
> it's write_irq_affinity() introduced by Mike Travis in kernel/irq/proc.c. It doesn't look
> like a hot path as it's file operations handler. If no objections from Mike or Thomas,

No objections from me as long as you can still change irq affinity using 
a cpulist instead of a cpumask.

Thanks,
Mike Travis


> I think it would make sense to copy_from_user() the userspace data at the beginning
> in sake of simplicity of __bitmap_parselist(), as you suggested above.
> 
> Yury
>