[RFC PATCH 17/17] KVM: PPC: Add an ioctl for userspace to select which platform to emulate

[Avi Kivity]

On 06/29/2011 02:58 PM, Josh Boyer wrote:
> >>  This makes me wonder if a similar thing might eventually be usable for
> >>  running an i686 or x32 guest on an x86_64 KVM host.  I have no idea if
> >>  that is even theoretically possible, but if it is it might be better to
> >>  rename the ioctl to be architecture agnostic.
> >
> >On x86 this is not required unless we want to "virtualize" pre-CPUID CPUs. Everything as of Pentium has a full bitmap of feature capabilities that KVM gets from user space, including information such as "Can we do 64-bit mode?".
>
> Ah.  Thank you for the explanation.

To clarify a bit further, running an i686 guest on an x86_64 host is not 
only theoretically possible, but is done regularly.  First, x86_64 is 
backwards compatible with i686 (so you can install a 32-bit OS on 64-bit 
hardware), and second, you can impersonate 32-bit guest hardware on a 
64-bit host.

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