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SubjectRe: [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driver objects
On 08/18/2009 01:28 PM, Michael S. Tsirkin wrote:
>
>> Suppose a nested guest has two devices. One a virtual device backed by
>> its host (our guest), and one a virtual device backed by us (the real
>> host), and assigned by the guest to the nested guest. If both devices
>> use hypercalls, there is no way to distinguish between them.
>>
> Not sure I understand. What I had in mind is that devices would have to
> either use different hypercalls and map hypercall to address during
> setup, or pass address with each hypercall. We get the hypercall,
> translate the address as if it was pio access, and know the destination?
>

There are no different hypercalls. There's just one hypercall
instruction, and there's no standard on how it's used. If a nested call
issues a hypercall instruction, you have no idea if it's calling a
Hyper-V hypercall or a vbus/virtio kick.

You could have a protocol where you register the hypercall instruction's
address with its recipient, but it quickly becomes a tangled mess. And
for what? pio and hypercalls have the same performance characteristics.

--
error compiling committee.c: too many arguments to function



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