linux-kernel - Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer

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Date:	Mon, 06 Apr 2009 10:53:40 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Pekka Paalanen <pq@....fi>
CC:	Masami Hiramatsu <mhiramat@...hat.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Jim Keniston <jkenisto@...ibm.com>, kvm@...r.kernel.org,
	systemtap-ml <systemtap@...rces.redhat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip 0/6 V4] tracing: kprobe-based event tracer

Pekka Paalanen wrote:
> Not just emulation but address diversion, i.e. modifying the operation
> (not the text) before executing it. Mmiotrace could do something like
> this:
> 1. a blob calls ioremap
> 2. mmiotrace maps the MMIO area privately
> 3. the blob receives a dummy map from ioremap, that will generate
> page fault
> 4. the blob accesses the dummy map and raises a page fault
> 5. pf handler detects the dummy map
> 6. mmiotrace pf handler emulates the instruction and replaces the
> dummy address with the real MMIO address.
> 7. mmiotrace records the operation and the datum
> 8. go to step 4, or whatever
>
> This means mmiotrace would not have to fiddle with the page
> tables and page presence bits like it does now. As said, this
> would make mmiotrace SMP-proof, and also eliminate the die notifier
> (used for the instruction single stepping trap).
>
> IMO a big step from a hack to a tool. Getting rid of the custom
> instruction parser in mmiotrace would be a good step in itself.
>
> Avi Kivity noted, that the KVM emulator does almost everything. Does
> it allow also address diversion?
>   

Operand access is by means of a callback, so yes.  In kvm's use, it's 
used to access guest memory, so it modified the addresses before reading 
or writing.

-- 
error compiling committee.c: too many arguments to function

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