Re: [Qemu-devel] RFC: ioapic polarity vs. qemu os-x guest

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Feb 14, 2014 at 11:13:04PM +0100, Alexander Graf wrote:
> 
> On 14.02.2014, at 23:06, Gabriel L. Somlo <gsomlo@gmail.com> wrote:
> 
> > On Fri, Feb 14, 2014 at 10:21:09PM +0100, Alexander Graf wrote:
> >> 
> >> Can't you just turn the polarity around in the pci host adapter?
> > 
> > I tried this:
> > 
> > diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> > index 1221f32..0e86d21 100644
> > --- a/hw/pci/pci.c
> > +++ b/hw/pci/pci.c
> > @@ -118,13 +118,13 @@ static int pci_bar(PCIDevice *d, int reg)
> > 
> > static inline int pci_irq_state(PCIDevice *d, int irq_num)
> > {
> > -	return (d->irq_state >> irq_num) & 0x1;
> > +	return !(d->irq_state >> irq_num) & 0x1;
> > }
> > 
> > static inline void pci_set_irq_state(PCIDevice *d, int irq_num, int level)
> > {
> > 	d->irq_state &= ~(0x1 << irq_num);
> > -	d->irq_state |= level << irq_num;
> > +	d->irq_state &= ~(level << irq_num);
> > }
> > 
> > static void pci_change_irq_level(PCIDevice *pci_dev, int irq_num, int change)
> > @@ -229,7 +229,7 @@ static void pcibus_reset(BusState *qbus)
> >     }
> > 
> >     for (i = 0; i < bus->nirq; i++) {
> > -        assert(bus->irq_count[i] == 0);
> > +        assert(bus->irq_count[i] != 0);
> >     }
> > }
> > 
> > ---
> > 
> > but now OS X freezes during boot right after
> > 
> > 	[ PCI configuration begin ]
> > 	[ PCI configuration end, bridges 1, devices 10 ]
> > 	RTC: Only single RAM bank (128 bytes)
> > 
> > which all looks normal, except the process is supposed to continue on
> > from there and doesn't :)
> > 
> > On Linux, I get Fedora 20 live all the way up with no obvious/loud
> > complaints, but mouse and keyboard don't work at all...
> > 
> > I have to admit I'm a bit out of my depth here, though :)
> 
> Yeah, another thing we have to take into account is vhost-net which generates IRQs directly through irqfd. I guess for those we'll have to configure the polarity in the irq routing table?
> 
> 
> Alex

What will be affected is VFIO which uses IRQFD
for level interrupts with KVM_IRQFD_FLAG_RESAMPLE.
I suspect this will need a kernel change, maybe
a new flag for IRQFD: KVM_IRQFD_FLAG_ACTIVE_LOW,
since at the moment that does:

static void
irqfd_inject(struct work_struct *work)
{
        struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
        struct kvm *kvm = irqfd->kvm;

        if (!irqfd->resampler) {
                kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1,
                                false);
                kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0,
                                false);
        } else
                kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID,
                            irqfd->gsi, 1, false);
}



-- 
MST