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


From: Alex Williamson
Subject: Re: [Qemu-devel] RFC: ioapic polarity vs. qemu os-x guest
Date: Sun, 16 Feb 2014 07:47:00 -0700

On Sun, 2014-02-16 at 13:41 +0200, Michael S. Tsirkin wrote:
> On Fri, Feb 14, 2014 at 11:13:04PM +0100, Alexander Graf wrote:
> > 
> > On 14.02.2014, at 23:06, Gabriel L. Somlo <address@hidden> 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);
> }



As you said in a previous message, devices just want assert & de-assert,
1 & 0, which is what we have here.  I would think that what asserted
means only needs to be interpreted at the IOAPIC, so I'd hope we could
get it right w/o an API change.  Thanks,

Alex




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