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SubjectRe: [RFC] CPUID usage for interaction between Hypervisors and Linux.
Jeremy Fitzhardinge wrote:
>>
>> 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.
>

Not necessarily, although the example above is extreme. Redundant
interfaces is the norm in an evolving platform.

>> 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).

Not inherently. Of course, there may be interfaces which are interently
or by policy mutually exclusive, but a hypervisor should only export the
interfaces it wants a guest to be able to use.

This is particularly so with CPUID, which is a *data export* interface,
it doesn't perform any action.

-hpa


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