linux-kernel - Re: [PATCH 0/2] mm: introduce MAP_FIXED

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Message-ID: <c427dc00-2835-a475-1ef5-f5550c4113a0@nvidia.com>
Date:   Wed, 6 Dec 2017 17:08:19 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        Michael Kerrisk <mtk.manpages@...il.com>
CC:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Michael Ellerman <mpe@...erman.id.au>,
        Linux API <linux-api@...r.kernel.org>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
        Joel Stanley <joel@....id.au>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE

On 12/06/2017 04:19 PM, Kees Cook wrote:
> On Wed, Dec 6, 2017 at 1:08 AM, Michal Hocko <mhocko@...nel.org> wrote:
>> On Wed 06-12-17 08:33:37, Rasmus Villemoes wrote:
>>> On 2017-12-06 05:50, Michael Ellerman wrote:
>>>> Michal Hocko <mhocko@...nel.org> writes:
>>>>
>>>>> On Wed 29-11-17 14:25:36, Kees Cook wrote:
>>>>> It is safe in a sense it doesn't perform any address space dangerous
>>>>> operations. mmap is _inherently_ about the address space so the context
>>>>> should be kind of clear.
>>>>
>>>> So now you have to define what "dangerous" means.
>>>>
>>>>>> MAP_FIXED_UNIQUE
>>>>>> MAP_FIXED_ONCE
>>>>>> MAP_FIXED_FRESH
>>>>>
>>>>> Well, I can open a poll for the best name, but none of those you are
>>>>> proposing sound much better to me. Yeah, naming sucks...
>>>
>>> I also don't like the _SAFE name - MAP_FIXED in itself isn't unsafe [1],
>>> but I do agree that having a way to avoid clobbering (parts of) an
>>> existing mapping is quite useful. Since we're bikeshedding names, how
>>> about MAP_FIXED_EXCL, in analogy with the O_ flag.
>>
>> I really give up on the name discussion. I will take whatever the
>> majority comes up with. I just do not want this (useful) funtionality
>> get bikeched to death.
> 
> Yup, I really want this to land too. What do people think of Matthew
> Wilcox's MAP_REQUIRED ? MAP_EXACT isn't exact, and dropping "FIXED"
> out of the middle seems sensible to me.

+1, MAP_REQUIRED does sound like the best one so far, yes. Sorry if I contributed
to any excessive bikeshedding. :)

thanks,
john h

> 
> MIchael, any suggestions with your API hat on?
> 
> -Kees
>