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

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Jean-Eric wrote:

> I have a question:
> What is the difference between a std Linux kernel and an xen0 one? 
> Except that we can run xenU instances in the xen0 one...
A standard Linux kernel expects to manage it's own memory, hardware, 
etc.  A xen kernel knows that it's in a hypervisor so it makes 
hypercalls when it needs to deal with those sorts of things.  That's a 
pretty gross simplification but you can check out any number of the 
papers referenced on the Xen homepage for whatever level of detail you want.
> 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.  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.
Really, the biggest difference is that xen0 domain has backend device 
drivers and the xenU kernel has the front-end version of those drivers.
> 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 shouldn't decrease performance.  Currently, xen0 is pretty much a 
single point of failure though.  If you had a remote comprimise in xen0 
then an attack could bring down every other domain.
Regards,
Anthony Liguori


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