Re: [Qemu-devel] [PATCHv3] piix: fix up/down races

[Michael S. Tsirkin]

On Tue, Apr 03, 2012 at 02:40:41AM -0400, Igor Mammedov wrote:
> > > +     */
> > > +    s->pci0_status.down &= ~(1U << slot);
> > 
> > Should we clear "up" here too?
> Is it possible to create pci dev for not yet freed pci slot?

It's not possible ATM.

> If not then we should not care, otherwise we should fix that.
> > > @@ -567,8 +595,6 @@ static int piix4_device_hotplug(DeviceState
> > > *qdev, PCIDevice *dev,
> > >          return 0;
> > >      }
> > >  
> > > -    s->pci0_status.up = 0;
> > > -    s->pci0_status.down = 0;
> > >      if (state == PCI_HOTPLUG_ENABLED) {
> > >          enable_device(s, slot);
> > >      } else {
> > 
> > So if we have an old bios and do an add, followed by a remove, guest
> > ACPI finds both "up" and "down" set for the slot and we rely on the
> > ordering of the AML checking up before down to keep the duct tape and
> > bailing wire from exploding?

In fact UP triggers a rescan - there is no injection event in ACPI.
So it seems you can check the events in any order.

> >  Hmm, can't say I'm excited about this
> > hack
> > either.  Thanks,
> > 
> > Alex
> > 
> >