Re: [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd

Michael S. Tsirkin
2012-09-05T14:50:32Z

On Wed, Sep 05, 2012 at 05:35:43PM +0300, Avi Kivity wrote:
> On 08/22/2012 03:41 AM, Michael S. Tsirkin wrote:
> >>
> >> I assumed you were pointing out the level vs edge interaction. If we
> >> call that a userspace bug, I can just drop this. Thanks,
> >>
> >> Alex
> >
> > level is userspace bug I think :)
>
> I don't see how it's a bug. Suppose we have a vfio device that shares a
> gsi with an emulated device. The emulated device naturally uses
> KVM_IRQ_LINE (it has no need to re-sample on ADN), while vfio naturally
> has to use irqfd.

Absolutely. But vfio needs to use irqfd with the new flag.
Using existing irqfd for level is a bug.

> Note one would expect that each irqfd gets its own irq source id, since
> they are all independent level sources. The reason they don't is that
> we shut them down anyway and let the sources re-trigger (it is more
> accurate to say that they have no irq source id, but that would just
> muddle the implementation).
>
> Alex, if the conclusion is that we do need this patch, then please add a
> comment explaining why we can share the source id among all irqfd users.
>
> --
> error compiling committee.c: too many arguments to function