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    SubjectRe: [RFC] CPUID usage for interaction between Hypervisors and Linux.
    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.
    >
    > Or are you suggesting that multiple interfaces be _available_ to guests at runtime but the guest chooses one of them?
    >

    The guest chooses what it wants to use. We already do this: for
    example, we use CPUID leaf 0x80000006 preferentially to CPUID leaf 2,
    simply because it is a better interface.

    And you're absolutely right that the guest may end up picking and
    choosing different parts of the interfaces. That's how it is supposed
    to work.

    -hpa


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