Re: [RFC PATCH 0/3] generic hypercall support

Avi Kivity
2009-05-10T10:02:06Z

Gregory Haskins wrote:
>>
>> That only works if the device exposes a pio port, and the hypervisor
>> exposes HC_PIO. If the device exposes the hypercall, things break
>> once you assign it.
>>
>
> Well, true. But normally I would think you would resurface the device
> from G1 to G2 anyway, so any relevant transform would also be reflected
> in the resurfaced device config.

We do, but the G1 hypervisor cannot be expected to understand the config
option that exposes the hypercall.

> I suppose if you had a hard
> requirement that, say, even the pci-config space was pass-through, this
> would be a problem. I am not sure if that is a realistic environment,
> though.
>

You must pass through the config space, as some of it is device
specific. The hypervisor will trap config space accesses, but unless it
understands them, it cannot modify them.

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