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

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Date:	Wed, 9 Jan 2008 21:08:26 +0100
From:	Andi Kleen <ak@...e.de>
To:	Pekka Paalanen <pq@....fi>
Cc:	Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>,
	hch@....de, airlied@...ux.ie, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, 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"


> 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?

Probes are generally not designed to change the flow of the 
underlying code.

While it's in theory possible it will be always unreliable.

For checks that result in logic changes you'll always need
some kind of explicit hook.

-Andi



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