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

[Gleb Natapov]

On Sun, Dec 20, 2009 at 07:18:22PM +0200, Michael S. Tsirkin wrote:
> On Sun, Dec 20, 2009 at 06:17:02PM +0100, Alexander Graf wrote:
> > 
> > On 20.12.2009, at 17:56, Michael S. Tsirkin wrote:
> > 
> > > On Sun, Dec 20, 2009 at 05:59:33PM +0200, Avi Kivity wrote:
> > >> On 12/20/2009 05:51 PM, Michael S. Tsirkin wrote:
> > >>> 
> > >>>> Maybe we should make -cpu host the default.  That will give the best
> > >>>> performance for casual users, more testing for newer features, and will
> > >>>> force management apps to treat migration much more seriously.  The
> > >>>> downside is that casual users upgrading their machines might experience
> > >>>> issues with Windows.  Feature compatibility is not just about 
> > >>>> migration.
> > >>>> 
> > >>> This seems very aggressive.  Can't we whitelist features that we know
> > >>> about?  Further, doesn't KVM already do this?
> > >>> 
> > >>> 
> > >> 
> > >> It does, but without -cpuid host you're stuck with qemu64 (kvm.ko  
> > >> doesn't add features userspace didn't request).
> > > 
> > > Hmm, then, shouldn't either kvm or qemu mask features that we do not
> > > emulate well enough to make windows not crash?
> > 
> > -cpu host does that already, no?
> > 
> > Alex
> 
> I expected so, but Avi here seems to say windows will crash if you
> use a new CPU with it ...
> 
Windows _may_ crash if you'll _upgrade_ your _host_ CPU.

--
                        Gleb.