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Date: Mon, 9 Jul 2001 10:42:25 -0700 (PDT)
From: Linus Torvalds <torvalds@transmeta.com>
To: Hugh Dickins <hugh@veritas.com>
cc: Andrea Arcangeli <andrea@suse.de>, Andrew Morton <andrewm@uow.edu.au>,
        Abraham vd Merwe <abraham@2d3d.co.za>,
        Linux Kernel Development <linux-kernel@vger.kernel.org>
Subject: Re: msync() bug
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On Mon, 9 Jul 2001, Hugh Dickins wrote:
> >
> > that cannot happen, remap_pte_range only maps invalid pages or reserved
> > pages.
>
> Anyone know why mmap() of /dev/mem behaves in this way - solves the
> problem Andrew raises, but surely that could be solved in a better way?
> Seems strange that mmap() cannot give you what read() and write() can.

Simple: we MUST NOT muck around with the page counts of random pages.

And if the pages aren't marked Reserved, the page counts _would_ get
corrupted by the VM page handling.

Ergo: you can only mmap Reserved pages (or you have to create a nice
mapping and allocate the pages properly, which in the case of /dev/mem is
obviously not a possibility)

		Linus

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