Re: [PATCH 0/8][v2] MSI-X mask emulation support for assigned device

Avi Kivity
2010-10-20T15:17:07Z

On 10/20/2010 03:43 PM, Michael S. Tsirkin wrote:
> > >If instead of eventfd we had a file descriptor that can pass vector
> > >information from vfio to kvm and back, that would fix it,
> > >as we would not need to set us GSIs at all,
> > >and not need for userspace to handle MSIX specially.
> > >
> >
> > But if we emulate the entire msix bar in vfio, that's not needed, right?
>
> Yes, I think it is. How does kvm know which interrupt to inject?
> Either vfio needs to pass that info to qemu and qemu would pass it
> to kvm, or vfio would have some way to pass that info to kvm
> directly.

Wait. We can't emulate the BAR in vfio, we have to emulate it in kvm
where we emulate the write instruction. We then need to tell vfio,
perhaps via userspace, that masking state has changed.

Seems very intrusive.

We can perhaps use the new semaphore capability in eventfd to pass
mask/unmask information from kvm to userspace. We'd usually hook it to
the corresponding vfio facility.

> > How far away is vfio? If it's merged soon, we might avoid making
> > changes to the old assigned device infrastructure and instead update
> > vfio.
>
> Hard to be sure, hopefully 2.6.38 material.

My question was how to implement this with vfio. But your list is
interesting as well.

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