Re: Linux in VirtualPC in KVM fails

Avi Kivity
2009-01-09T19:32:23Z

Anthony Liguori wrote:
> Alexander Graf wrote:
>>
>> Shouldn't it be ok to push patches to linux-stable to use the CPUID
>> and MSR information and simply not expose the CPUID identification in
>> newer KVM versions? That way older guests on newer KVM don't use KVM
>> paravirt (which should still be ok), but everything else runs as
>> smoothly as possible.
>
> I'd say that VirtualPC is broken and leave it at that.
>
> All modern hypervisors use CPUID to expose themselves to the guests.
> VirtualPC is totally capable of rewriting CPUID instructions.

Apparently it isn't. I know of one other fullvirt product that does not
jit kernel code. Or maybe they wanted to preserve consistency between
kernel cpuid and host cpuid.

> Shame on it for not doing so. I don't think we should change anything.

PC hardware and software are full of examples of such brokenness. One
of the most painful examples is Linux using the tsc for time of day
despite the fact that the tsc was explicitly advertised not to be fit
for that role.

If there's an easy and backwards compatible way to support Virtual PC,
we should implement it.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.