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

Avi Kivity
2010-10-20T15:23:54Z

On 10/20/2010 04:47 PM, Alex Williamson wrote:
> >
> > With current VFIO we would catch mask writes in qemu and
> > call a KVM ioctl. We would also need an ioctl to retrieve
> > pending bits long term.
>
> Ugh, no. VFIO us currently independent of KVM. I'd like to keep it
> that way.

Me, too. Perhaps even more than you.

> We'll need to optimize interrupt injection and eoi via KVM,
> but it should only be a performance optimization, not a functional
> requirement.

For level-triggered interrupts only, yes? MSI EOI does not involve any
device or interrupt controller visible action?

> It would probably make sense to request a mask/unmask ioctl in VFIO for
> MSI-X, then perhaps the pending bits would only support read/write (no
> mmap), so we could avoid an ioctl there.

I would much like to see in-band information (which mask/unmask is for
older Linux) done via eventfds so userspace is not involved.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.