[Qemu-devel] Re: [PATCH] introduce kvm64 CPU

[Jamie Lokier]

Avi Kivity wrote:
> On 08/22/2009 12:59 AM, Andre Przywara wrote:
> >>Typically users will want more specialized greatest common denomiator 
> >>cpu types; if a site has standardized on recent hardware they will 
> >>want the features of that hardware exposed.
> >Sure, but this was not the purpose of this patch. Currently KVM guests 
> >see a CPU type which is TCG dependent, so I just wanted to get rid of 
> >this. Features of TCG and features of the host processor are totally 
> >uncorrelated. This new type should be KVM's default, leaving -cpu host 
> >as the alternative for the non-migration case.
> 
> That does make sense.  Note we can call it '-cpu kvm' since qemu will 
> strip away long mode if it is not supported by the cpu or by the kernel.

I thought the point was to provide a "lowest common denominator" for
migration, while acknowledging that 64-bit is too useful to exclude?

So if you start running on a 64-bit host, but know you have 32-bit
hosts in your pool, you'll need '-cpu kvm32'.

And if you start on a 32-bit host, but want to migrate to a 64-bit
host, will that work if the destination has different cpuid than the
source?

-- Jamie