Re: [PATCH 3/8] KVM: Handle device assignment to guests

Ben-Ami Yassour
2008-07-17T17:41:25Z

On Thu, 2008-07-17 at 12:50 +0300, Avi Kivity wrote:
> Ben-Ami Yassour wrote:
> > On Wed, 2008-07-16 at 18:04 +0300, Avi Kivity wrote:
> >
>
> If a level triggered interrupt remains active after the eoi, the ioapic
> has to inject it. This is used to support shared interrupts, or when
> the device has re-raised the line by the time the ack arrives.
>
> I don't see why it should behave differently for assigned devices.
>

The difference is that for emulated devices, qemu is resetting the irr
bit. For assigned devices it does not, and that's the difference.
The first chance that we can clear the irr bit for real devices is the
eoi function, and actually this is what the ack notify handler is doing
(by calling ﻿﻿pci_set_irq(kvm,irq,0) ).
I was able to remove the code in ioapic by calling the ack notify
handler before the irr check, and it seems to work fine.
(to make it work, I also had to remove the queuing of the ack handler
which was not necessary, as you mentioned in earlier comment)

The eoi function now looks like this:
static void __kvm_ioapic_update_eoi(struct kvm_ioapic *ioapic, int gsi)
{
union ioapic_redir_entry *ent;

ent = &ioapic->redirtbl[gsi];
ASSERT(ent->fields.trig_mode == IOAPIC_LEVEL_TRIG);

ent->fields.remote_irr = 0;

if (ioapic->ack_notifier)
ioapic->ack_notifier(ioapic->kvm, gsi);

if (!ent->fields.mask && (ioapic->irr & (1 << gsi)))
ioapic_service(ioapic, gsi);
}

Any comments on such an approach?

Thanks,
Ben