Re: [Xen-users] How to get dom0 configuration when running in domU?

[Hannes Kuehnemund <hannes.kuehnemund@xxxxxxx>]

Petersson, Mats wrote:
> > -----Original Message-----
> > Hi,
> >
> > is there any chance to get the dom0 configuration information 
> > (which is 
> > available in dom0 by 'xm list --long Domain-0' or 'xm vcpu-list' in 
> > general) being in a domU?
> > The background is, only having access to domU I'd like to know the 
> > mapping of my virtual CPU's. How can I figure out if my 4 
> > virtual CPU's 
> > aren't assigned to one single physical CPU. This information 
> > is needed 
> > for sizing matters.
> This information SHOULDN'T be available to the guest for security
> reasons - guest shouldn't even be able to tell that it's not a physical
> machine [although this is probably not to hard to do with "uname -a" or
> by measuring the timing of certain operations]. I'm not sure if you can
> trick around and for example read CPUID to find the APICID of the
> VCPU's, for example [probably not, because that would break SMP in
> guest, I think]. 
>
> Some possible option(s) for checking this are:
> 1. use some sort of network protocol to get back to Dom0 (or a client
> supported by Dom0). Most trivial is "ssh <dom0> xm ...".
>
> 2. Try to determine it by running variable loads on the guest - such as
> run one thread, then two threads, then three, then four (etc).  If you
> have fewer physical CPU's than VCPU's, then there will be a proportional
> slow-down per thread when you get above the number of physical CPU's.
> [That is, of course, if you don't have any other competing tasks on the
> same physical CPU(s), but then on the other hand, if you have four
> physical CPU's, but share them with another guest, that would amount to
> the same thing as not having a "full" set of CPUs in the first place,
> right?]. 
Thanks for your comments so far. I agree, that this information 
shouldn't be available by DEFAULT. But if I want this information, and I 
 have control over dom0, there must be a way to get it. I agree, that a 
domU should not get any information if this feature is not enabled in 
dom0 (which should be the default)!
Of course one can install some remote management software in every domU 
which queries a configured dom0, but after a migration this will not 
work, as the dom0 the domU is running on changed.
This feature is already available on zOS and VMWare (through the VMWare 
SDK), thus it should also be available on Xen.
But taken from your answer, this feature is sadly not yet available. 
Anyway, does anyone know where to ask for new features of Xen?
> --
> Mats
Thanks,
  Hannes

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