RE: [Xen-devel] Xen-aware kernel module

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> Hello,
> 
> (I'm not sure if this is an appropriate place to ask this question. I
> apologize, if it's not)
> 
> I'm trying to write a kernel module, that's sort of Xen-aware (or
> virtualisation-aware). I say "sort of", because what I actually need
> is checking the ring. Specifically, in my kernel module, I want to
> check which ring the code is running on (ring0, ring1, or even ring
> 3!), and behave differently. Does Xen provide any interface to do it?
> or is there any way to do it in a kernel module? Thanks for any help.

There may or may not be a CPU instruction to tell you what RING you are
running in.

As for telling if you are running under Xen, have a look at
/unmodified_drivers/linux-2.6/platform-pci/platform-pci.c in the
function init_hypercall_stubs. The first thing it does is execute a
CPUID instruction. If Xen is running, a signature will be encoded into
EBX, ECX, and EDX. You might be able to make use of that?

James

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