linux-kernel - Re: [PATCH] Revert "x86: optimize page faults like all other achitectures and kill notifier cruft"

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Message-ID: <20080109220148.5caebaf1@daedalus.pq.iki.fi>
Date:	Wed, 9 Jan 2008 22:01:48 +0200
From:	Pekka Paalanen <pq@....fi>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	David Miller <davem@...emloft.net>, hch@....de, airlied@...ux.ie,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	ak@...e.de, jbeulich@...ell.com, linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Masami Hiramatsu <mhiramat@...hat.com>
Subject: Re: [PATCH] Revert "x86: optimize page faults like all other
 achitectures and kill notifier cruft"

On Wed, 9 Jan 2008 11:41:49 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> i agree. There a few practical complication on x86: the
> do_page_fault() function is currently excluded from kprobe probing,
> for recursion reasons. handle_mm_fault() can be probed OTOH - but
> that does not catch vmalloc()-ed faults. The middle of
> do_page_fault() [line 348] should work better [the point after
> notify_page_fault()] - but it's usually more fragile to insert probes
> to such middle-of-the-function places.

I have been reading about kprobes and one thing particularly bothers me
in the case of mmio-trace. The probe will actually service the page
fault, therefore it should be able force do_page_fault() to return at
the probe point. I could not figure out a way to do that.

Is it possible to do reliably with kprobes or markers?


Thanks for the replies.

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