Re: [RFC] CPUID usage for interaction between Hypervisors and Linux.

[Jeremy Fitzhardinge <jeremy@goop.org>]

Nakajima, Jun wrote:
> On 10/3/2008 5:35:39 PM, H. Peter Anvin wrote:
>   
>> Nakajima, Jun wrote:
>>     
>>> What's the significance of supporting multiple interfaces to the
>>> same guest simultaneously, i.e. _runtime_? We don't want the guests
>>> to run on such a literarily Frankenstein machine. And practically,
>>> such testing/debugging would be good only for Halloween :-).
>>>
>>>       
>> By that notion, EVERY CPU currently shipped is a "Frankenstein" CPU,
>> since at very least they export Intel-derived and AMD-derived interfaces.
>>  This is in other words, a ridiculous claim.
>>     
>
> The big difference here is that you could create a VM at runtime (by combining the existing interfaces) that did not exist before (or was not tested before). For example, a hypervisor could show hyper-v, osx-v (if any), linux-v, etc., and a guest could create a VM with hyper-v MMU, osx-v interrupt handling, Linux-v timer, etc. And such combinations/variations can grow exponentially.
>   

That would be crazy.

> Or are you suggesting that multiple interfaces be _available_ to guests at runtime but the guest chooses one of them?
>   

Right, that's what I've been suggesting.    I think hypervisors should 
be able to offer multiple ABIs to guests, but a guest has to commit to 
using one exclusively (ie, once they start to use one then the others 
turn themselves off, kill the domain, etc).

    J