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SubjectRe: disabling group leader perf_event

* Avi Kivity <> 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

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


> 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.



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