Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE

From: John Hubbard <jhubbard@nvidia.com>
To: Kees Cook <keescook@chromium.org>,
	Michal Hocko <mhocko@kernel.org>,
	Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Linux API <linux-api@vger.kernel.org>,
	Khalid Aziz <khalid.aziz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Florian Weimer <fweimer@redhat.com>,
	Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
	Joel Stanley <joel@jms.id.au>,
	Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE
Date: Wed, 6 Dec 2017 17:08:19 -0800	[thread overview]
Message-ID: <c427dc00-2835-a475-1ef5-f5550c4113a0@nvidia.com> (raw)
In-Reply-To: <CAGXu5jKGsAjwF7nE_vjaWPnG0QJRx_qFeiSBLRg_g73iUJ-pwA@mail.gmail.com>

On 12/06/2017 04:19 PM, Kees Cook wrote:
> On Wed, Dec 6, 2017 at 1:08 AM, Michal Hocko <mhocko@kernel.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@kernel.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
> 

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