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

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.

Anthony Liguori

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