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

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Date:   Wed, 6 Dec 2017 09:54:30 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     John Hubbard <jhubbard@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Cyril Hrubis <chrubis@...e.cz>, Michal Hocko <mhocko@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        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>,
        Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
        Joel Stanley <joel@....id.au>
Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE

On 12/06/2017 09:06 AM, John Hubbard wrote:
> On 12/05/2017 11:35 PM, Florian Weimer wrote:
>> On 12/06/2017 08:33 AM, John Hubbard wrote:
>>> In that case, maybe:
>>>
>>>       MAP_EXACT
>>>
>>> ? ...because that's the characteristic behavior.
>>
>> Is that true?  mmap still silently rounding up the length to the page size, I assume, so even that name is misleading.
> 
> Hi Florian,
> 
> Not as far as I can tell, it's not doing that.
> 
> For both MAP_FIXED, and this new flag, the documented (and actual)
> behavior is *not* to do any such rounding. Instead, the requested
> input address is required to be page-aligned itself, and mmap()
> should be honoring the exact addr.

I meant the length, not the address.

Florian