On 03/21/2013 07:43 AM, Michael S. Tsirkin wrote:
>>
>> The reason to support this is that a guest written to only handle one or
>> the other doesn't prevent the hypervisor from offering the other to
>> guests. We probably want to specify that if the guest doesn't care, it
>> should use the first one offered by the host.
>>
>
> What are the configurations where having many ways is helpful?
> Any examples?
>
In BIOS (e.g. SeaBIOS), using MMIO is very difficult, so your boot ROM
probably wants to use I/O space even if MMIO is available.
If you are preferring I/O space because it is faster (vmexit), then you
still want to allow MMIO if the resource is not available.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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