Re: [Xen-devel] Diff between std, xen0 and xenU kernel

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

> > And is the xen0 instance different from the xenU instances? Or is it
> > just another xenU instance in fact?
>
> A little bit.  It mostly has to do with the initrd setup code. 

Is it not the same for both?  What's different?

> However, 
> I think there was a thread on a list where someone said you could in
> fact use a xen0 kernel within xenU if you had the right drivers enabled.

Xen0 kernels will run in an unprivileged domain so long as you have built in 
the frontend drivers (this happens by default in -testing and -stable, I 
think).

> Really, the biggest difference is that xen0 domain has backend device
> drivers and the xenU kernel has the front-end version of those drivers.

The Xen0 kernel also has drivers for "real" hardware, whereas the xenU kernel 
contains only "virtual" drivers.  The xenU kernel is smaller as a result, 
which is the reason we provided.  You don't strictly *need* the xenU kernel 
at all.

> > And if I run programs in the xen0 instance, will it degrade perf of
> > xenU instances? Or render them less secure (in term of isolation)?

It won't matter to performance any more than running applications in the 
unprivileged instances would.

Regarding security you need to keep in mind that an attacker who gains root 
privileges in domain 0 will be able to get root privileges in every domain on 
the machine.  Thus if you're running an internet-facing machine you should 
make sure that domain 0 exposes as few services to the internet as possible.

Cheers,
Mark


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