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From: David Laight <David.Laight@ACULAB.COM>
Subject: RE: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE
Date: Fri, 8 Dec 2017 14:33:35 +0000
Message-ID: <0b0bd6862e3a47728c8f658c8a6b3dea@AcuMS.aculab.com>
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To: 'Michael Ellerman' <mpe@ellerman.id.au>, Matthew Wilcox <willy@infradead.org>, Kees Cook <keescook@chromium.org>
Cc: Cyril Hrubis <chrubis@suse.cz>, Michal Hocko <mhocko@kernel.org>, Linux
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From: Michael Ellerman
> Sent: 08 December 2017 11:08
...
> If we had a time machine, the right set of flags would be:
>=20
>   - 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)
>=20
> 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.
>=20
> ie: MAP_FIXED_NOREPLACE

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

	David

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