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

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Message-ID: <0b0bd6862e3a47728c8f658c8a6b3dea@AcuMS.aculab.com>
Date:   Fri, 8 Dec 2017 14:33:35 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Michael Ellerman' <mpe@...erman.id.au>,
        Matthew Wilcox <willy@...radead.org>,
        Kees Cook <keescook@...omium.org>
CC:     Cyril Hrubis <chrubis@...e.cz>, Michal Hocko <mhocko@...nel.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>,
        Florian Weimer <fweimer@...hat.com>,
        "John Hubbard" <jhubbard@...dia.com>,
        Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
        Joel Stanley <joel@....id.au>, Pavel Machek <pavel@....cz>
Subject: RE: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE

From: Michael Ellerman
> Sent: 08 December 2017 11:08
...
> If we had a time machine, the right set of flags would be:
> 
>   - MAP_FIXED:   don't treat addr as a hint, fail if addr is not free
>   - MAP_REPLACE: replace an existing mapping (or force or clobber)
> 
> But the two were conflated for some reason in the current MAP_FIXED.

Possibly because the original use was loading overlays?

> Given we can't go back and fix it, the closest we can get is to add a
> variant of MAP_FIXED which subtracts the "REPLACE" semantic.
> 
> ie: MAP_FIXED_NOREPLACE

Much better than _SAFE - which is always bad because it is usually
one 'safe' for one specific use case.

	David