Re: [Qemu-devel] cpuid problem in upstream qemu with kvm

[Gleb Natapov]

On Sun, Dec 20, 2009 at 07:06:03PM +0100, Alexander Graf wrote:
> 
> On 20.12.2009, at 18:59, Anthony Liguori wrote:
> 
> > Gleb Natapov wrote:
> >> Windows is a mystery box, so we can speculate as much as we want about it.
> >> If you don't like something just say "it may break Windows" :) Losing
> >> activation does sound like an issue too.
> >>  
> > 
> > Downgrading seems more likely to cause problems.  Considering running 
> > mplayer in a guest.  If it detects SSE3 in one host and migrate to another 
> > host that doesn't have SSE3, you'll be running an instruction stream that 
> > uses instructions the processor doesn't support resulting in the 
> > application faulting due to an illegal operation.
> 
> Yeah, migration with -cpu host doesn't sound like a sane thing to do.
> 
> > KVM's cpuid filter doesn't help here because it won't attempt to mask 
> > things like sse3.  It would be insane to emulate sse3 too.
> 
> Well, I wouldn't be too sure on that one. Software may use SSE3 instructions 
> to access MMIO in which case we do have to emulate it.
Unfortunately this is already a reality. Look here:
http://groups.google.com/group/linux.kernel/browse_thread/thread/ada9fa2d2574a8af


--
                        Gleb.