linux-kernel - Re: [RFC PATCH] x86: mmiotrace

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Date:	Thu, 31 Jan 2008 00:39:01 +0200
From:	Pekka Paalanen <pq@....fi>
To:	tglx@...utronix.de
Cc:	Pekka Paalanen <pq@....fi>, mingo@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] x86: mmiotrace - trace memory mapped IO

On Sun, 27 Jan 2008 19:55:36 +0200
Pekka Paalanen <pq@....fi> wrote:

> The following is a copy of the patch description:
...
> Mmiotrace works by wrapping the ioremap family of kernel functions and
> marking the returned pages as not present. Access to the IO memory
> triggers a page fault, which will be handled by mmiotrace's custom page
> fault handler. This will single-step the faulted instruction with the
> MMIO page marked as present. Access logs are directed to user space via
> relay and debug_fs.

Hi,

a test user found a problem with mmiotrace (ported to x86/mm git tree).
The symbol 'init_mm' is undefined, but required when building the 32-bit
mmiotrace kernel module.

commit 3abf024d2abb79614d8c4cb25a70d5596f77d0ad
Author: Thomas Gleixner <tglx@...utronix.de>
Date:   Wed Jan 30 13:30:28 2008 +0100

    x86: nuke a ton of unused exports

This commit removes EXPORT_SYMBOL(init_mm). Apparently mmiotrace requires
this symbol, but I do not know why. I do not use init_mm myself, so
apparently some function I call is inlined and requires it. Page table or
attribute handling stuff maybe?

Is it possible to simply put back this export or should I dig deeper into
why it seems to be required?
I can provide the simple patch to put it back in my next patch set, if
this is the right solution.

I will post the patch set after this issue is solved. In the mean time,
for the interested, the current patches are here:
http://jumi.lut.fi/~paalanen/scratch/mmio25/

Ps. I tested x86/mm version of mmiotrace on my 64-bit system and it seems
to work ok. I had to write a simple test module because I did not have any
drivers that a) called ioremap, b) were not broken on x86/mm, and c) I
had the hardware to actually use it. So this testing is very light.

-- 
Pekka Paalanen
http://www.iki.fi/pq/
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