On Friday 02 May 2008 16:05:17 Avi Kivity wrote:
> Amit Shah wrote:
> >>> +static irqreturn_t
> >>> +kvm_pci_pt_dev_intr(int irq, void *dev_id)
> >>>
> >>> +{
> >>> + struct kvm_pci_pt_dev_list *match;
> >>> + struct kvm *kvm = (struct kvm *) dev_id;
> >>> +
> >>> + if (!test_bit(irq, pt_irq_handled))
> >>> + return IRQ_NONE;
> >>> +
> >>> + if (test_bit(irq, pt_irq_pending))
> >>> + return IRQ_HANDLED;
> >>
> >> Will the interrupt not fire immediately after this returns?
> >
> > Hmm. This is just an optimisation so that we don't have to look up the
> > list each time to find out which assigned device it is and (re)injecting
> > the interrupt. Also we avoid the (TODO) getting/releasing locks which
> > will be needed for the list lookup.
> >
> > Disabling interrupts for PCI devices isn't a good idea even if we don't
> > support shared interrupts. Any other ideas to avoid this from happening?
>
> I don't understand. These are level-triggered interrupts, so if one
> fires and you don't disable it, it will fire again and again.
Yes, it does.
> Seems to me the only choice here is to mask the interrupt at the ioapic
> level, wait until the guest acks the interrupt, then unmask the interrupt.
OK; will that create problems if the line is shared?
> With the current code, how to the guest interrupt counters and the host
> interrupt counters compare?
The guest ticks along fine but the host count is quite huge. You're right in
your observations; what I was only suggesting was that disabling a shared
interrupt on the host while the guest acks it isn't a good idea.
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