[Qemu-devel] Re: UHCI idle detection

[Anthony Liguori]

On 01/04/2011 08:16 AM, Gerd Hoffmann wrote:
> On 01/04/11 14:49, Anthony Liguori wrote:
> > On 01/04/2011 07:43 AM, Gerd Hoffmann wrote:
> > > Hi,
> > >
> > > > > Windows guests needs some registry hackery and Linux guests some
> > > > > udev rules
> > > > > to enable remote wakeup permanently.
> > > >
> > > > That commit inspired me to look at UHCI. If the solution requires
> > > > modifying the guest then it is not widely useful.
> > >
> > > Well, long-term this shouldn't be a big issue. I expect guest agents
> > > become commonplace soonish as some features require guest cooperation,
> > > so the guest agents can also care about this kind of tweaks. Also for
> > > linux we can try to send the changes to upstream udev to have it
> > > spread into linux distros.
> >
> > I think we're long overdue for a paravirtual mouse. Basically, a virtio
> > version of xenkbd-front.c. In fact, it's probably possible to reuse the
> > protocol.
>
> Oh, there already is one.  vmmouse.  Recent Xorg versions even use it 
> automagically.  With Fedora 14 (as guest) you can drop the usb tablet 
> and you still have an absolute mouse pointer because of that ;)
>
> Windows is more tricky as it doesn't work out-of-the-box but that 
> wouldn't be different with a virtio-based mouse.

vmmouse relies on the VMware backdoor interface.  The backdoor interface 
requires that a certain PIO port be accessible from CPL=3 even if IOPL=0.

It works in Linux because Xorg generally changes IOPL=3 because it 
implements device drivers but in the long run, I hope that no longer 
becomes true.  With Windows, I've always been under the impression that 
their input driver runs in CPL=3 and there is no interface to change IOPL.

Supporting the backdoor interface properly in KVM would be really ugly.  
We'd have to shadow the IDT which means write protecting it and all of 
the ugliness that goes along with it.

Regards,

Anthony Liguori

> cheers,
>   Gerd