linux-kernel - Re: disabling group leader perf

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Date:	Mon, 6 Sep 2010 17:47:37 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Tom Zanussi <tzanussi@...il.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-perf-users@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: disabling group leader perf_event


* Avi Kivity <avi@...hat.com> wrote:

>  On 09/06/2010 03:59 PM, Ingo Molnar wrote:
> >
> >>Is this a roundabout way of saying "jit"?
> >Partly. I'm not sure we want to actually upload programs in bytecode
> >form. ASCII is just fine - just like a .gz Javascript is fine for web
> >apps. (and in most cases compresses down better than the bytecode
> >equivalent)
> >
> >So a clear language (the simpler initially the better) plus an in-kernel
> >compiler.
> >
> >This could be used for far more than just instrumentation: IMO security
> >policies could be expressed in such a way. (Simplified, they are quite
> >similar to filters installed on syscall entry/exit, with the ability of
> >the filter to influence whether the syscall is performed.)
> 
> For me the requirements are:
> - turing complete (more than just filters)

Yep. Filters are obviously just basically expressions.

Conditions and variables can be added. Maybe loops too in simpler forms 
- as long as we can prove halting - or maybe with a runtime abort 
mechanism.

> - easy interface to kernel APIs (like hrtimers)
> - safe to use by untrusted users

Yep.

> The actual language doesn't really matter.

There are 3 basic categories:

 1- Most (least abstract) specific code: a block of bytecode in the form 
    of a simplified, executable, kernel-checked x86 machine code block - 
    this is also the fastest form. [yes, this is actually possible.]

 2- Least specific (most abstract) code: A subset/sideset of C - as it's 
    the most kernel-developer-trustable/debuggable form.

 3- Everything else little more than a dot on the spectrum between the
    first two points.

I lean towards #2 - but #1 looks interesting too. #3 is distinctly 
uninteresting as it cannot be as fast as #1 and cannot be as convenient 
as #2.

Thanks,

	Ingo
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