linux-kernel - Re: mapping of pages out of upper 128MB into kernel address space

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Message-ID: <20061122182914.360752ef@localhost.localdomain>
Date:	Wed, 22 Nov 2006 18:29:14 +0000
From:	Alan <alan@...rguk.ukuu.org.uk>
To:	<pledr@...nline.de>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: mapping of pages out of upper 128MB into kernel address space

On 22 Nov 2006 18:05 GMT
<pledr@...nline.de> wrote:

> Hi,
> in a kernel module I have to translate user addresses into kernel addresses. The user uses shared memory allocated with shm_open / ftruncate. This shared memory is allocated somewhere in the upmost 128MB of physical memory that is NOT permanently mapped into the kernel ( found in swapper_pg_dir ). How can I "smp_save" map this memory into the kernel address space ?

See how copy_highpage and friends are used by copy_to/from_user. The
kmaps are a limited resource so you can only really use them to briefly
map objects in this way.

Alan
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