linux-kernel - Re: Forbid deletion of memory mappings

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Message-Id: <200708302341.09459.clemens.kol@gmx.at>
Date:	Thu, 30 Aug 2007 23:41:09 +0200
From:	Clemens Kolbitsch <clemens.kol@....at>
To:	linux-kernel@...r.kernel.org
Subject: Re: Forbid deletion of memory mappings

On Thursday 30 August 2007 23:34:52 you wrote:
> On Thu, 30 Aug 2007, Clemens Kolbitsch wrote:
> > is there no way to tell the kernel, that a certain mapping must not be
> > removed, no matter what (except of course an explicit call to sys_unmap,
> > of course)?
>
> I don't seem to get what is the issue here. Your mapping is not removed,
> only the VMAs are merged together into one larger VMA if they have
> neighbouring address ranges and compatible protection bits. See
> vma_merge().

the thing is that they are not. the kernel chooses to REPLACE my mapping.

consider the user-space code:

mmap(0xaaaa0000, 0x3000, MAP_FIXED, ...);
mmap(0xaaaa1000, 0x4000, MAP_FIXED, ...);

here, the second call to mmap will shorten the first mapping to 0x1000 bytes 
and create one big vma with size 0x5000 bytes.

is there a way to tell it that the second mmap MUST fail?


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