Re: [Xen-devel] Notes on stubdoms and latency on ARM

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Mon, 2017-06-19 at 11:26 -0700, Volodymyr Babchuk wrote:
> On 19 June 2017 at 02:37, George Dunlap <george.dunlap@xxxxxxxxxx>
> wrote:
> > If you want this "EL0 app" thing to be able to provide extra
> > security
> > over just running the code inside of Xen, then the code must not be
> > able
> > to DoS the host by spinning forever instead of returning.
> 
> Right. This is a problem. Fortunately, it is running with interrupts
> enabled, so next timer tick will switch back to XEN. There you can
> terminate app which is running too long.
> 
What timer tick? Xen does not have one. A scheduler may setup one, if
it's necessary for its own purposes, but that's entirely optional. For
example, Credit does have one; Credit2, RTDS and null do not.

Basically, (one of the) main purposes of this new "EL0 app mechanism"
is playing behind the scheduler back. Well, fine, but then you're not
allowed to assume that the scheduler will rescue you if something goes
wrong.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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