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From: Pekka Paalanen <pq@iki.fi>
To: linux-kernel@vger.kernel.org
Cc: jbeulich@novell.com, proski@gnu.org
Subject: Replacement for page fault notifiers?
Date: Tue, 8 Jan 2008 21:06:38 +0200	[thread overview]
Message-ID: <20080108210638.5c9e093a@daedalus.pq.iki.fi> (raw)

Hello,

the commit "x86: optimize page faults like all other achitectures and
kill notifier cruft" by Christoph Hellwig removed the page fault
notifiers (e.g. register_page_fault_notifier()) completely in 2.6.24.
Mmio-trace [1] is using them for tracking memory mapped IO, and also
other people have mentioned they need it [2,3].

This is roughly how I understand mmio-trace is working. In a loadable
kernel module calls to __ioremap() are diverted to an mmio-trace
specific function. The function calls the real __ioremap() and marks
the returned pages as not present. Access to the mapped IO memory
causes a page fault. Mmio-trace's page fault handler marks the page
present, records the event, single-steps the faulting instruction, and
finally marks the page as not present again.

- Is there anything coming to replace register_page_fault_notifier()?
- Has someone found another way to accomplish the same without patching
the kernel?
- Should I start writing a patch to bring back the notifiers, based on
the commit that removed them?

People started to complain to me that mmio-trace does not compile for
2.6.24. At least the Nouveau project is a regular user of mmio-trace
for reverse-engineering, and the tool should be easy to use. Therefore
I would prefer not to force casual contributors to patch their kernels
as it might be too much for some. I am hoping that 2.6.25, if not
2.6.24, would contain a mechanism to accomplish what I need.

I am not a subscriber, so please keep me in CC. Also I CC'd the people
who wrote about the same issue in the past.

Thanks.


[1] http://nouveau.freedesktop.org/wiki/MmioTrace
[2] http://marc.info/?l=linux-kernel&m=119540769014745&w=2
[3] http://article.gmane.org/gmane.linux.kernel/609521

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

             reply	other threads:[~2008-01-08 19:51 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-08 19:06 Pekka Paalanen [this message]
2008-01-08 20:32 ` Christoph Hellwig
2008-01-08 22:13   ` Dave Airlie
2008-01-09  0:26     ` Benjamin Herrenschmidt
2008-01-09 18:18       ` Pavel Roskin
2008-01-09 18:21         ` Christoph Hellwig
2008-01-09 19:58           ` Benjamin Herrenschmidt
2008-01-09 20:22             ` Christoph Hellwig
2008-01-10  0:42               ` Arjan van de Ven
2008-01-10  0:47                 ` Andi Kleen
2008-01-10  0:55                   ` Arjan van de Ven
2008-01-10  0:58                     ` Benjamin Herrenschmidt
2008-01-10  1:01                     ` Andi Kleen
2008-01-10  0:56                 ` Benjamin Herrenschmidt
2008-01-10  2:03                 ` Matt Mackall
2008-01-10  2:21                   ` Pavel Roskin
2008-01-10  2:30                     ` Matt Mackall
2008-01-10 18:44               ` Pekka Paalanen
2008-01-09 20:24             ` Pavel Roskin
2008-01-09 20:26               ` Christoph Hellwig
2008-01-09 20:41                 ` Pavel Roskin
2008-01-09 20:44                 ` Valdis.Kletnieks

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