Re: [Xen-devel] [RFC] Hypercalls from HVM guests

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 9 Apr 2006, at 14:56, Nakajima, Jun wrote:

> This is a different question, and I think detecting a virtual device
> (i.e. virtual block device, NIC) or chipset would be a cleaner way at
> this point. And that would be proper for the patch that Steve mentioned
> (we wrote it). The fact that it's running on a hypervisor does not
> necessarily guarantee presence of such virtual devices (in fact they
> don't exist today ;-).
>
> If we really need to tell if we are running on a hypervisor at a very
> early point or even in user-mode, I think CPUID with "an unused index"
> would be the simplest, but so far I haven't seen any usage models that
> really require that. If we want to add virtualization hints for
> processor architectures (e.g. MMU) in guests, it would be needed.
Executing hypercalls via an indirection page as we do for 
paravirtualised guests is an attractive idea. That would require more 
than just 'are we AMD or Intel' and it would be nice to have that 
future-proofing level of indirection in the initial implementation. We 
could do that via the PCI device too (e.g., use a BAR) though that 
doesn't seem so clean to me.
 -- Keir


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