Re: [PATCH 2/2][RFC] KVM: Emulate MSI-X table and PBA in kernel

Michael S. Tsirkin
2011-01-02T10:40:09Z

On Sun, Jan 02, 2011 at 12:26:11PM +0200, Avi Kivity wrote:
> On 12/31/2010 05:05 AM, Sheng Yang wrote:
> >>
> >> Existing code does not support PBA in assigned devices, so at least it's
> >> not a regression there, and the virtio spec says nothing about this so
> >> we should be fine.
> >
> >I agree. At least it's not a regression. And in fact we haven't seen any device
> >driver use this. I've checked Linux kernel code, found no one used PCI_MSIX_PBA or
> >msix_pba_offset_reg().
> >
> >I guess it's fine to get MSI-X mask part in first, then deal with PBA part if
> >necessary - though we haven't seen any driver use it so far. It won't be worse
> >with this patch anyway...
>
> In a way it is worse because before, the fix would belong in user
> space, which is easier to test and distribute. Now we have to fix
> it in the kernel.
>
> However I recognize that drivers which rely on the pending bit are
> rare/nonexistent (likely on in preboot environments where interrupts
> are hard), so even if we do code it, it will likely be incorrect
> (certainly without a test).
>
> So I'll accept the patch without PBA. Michael, what about
> supporting virtio? Can we base something on this patch?

I don't see how userspace can send interrupts with this
interface unfortunately. We also need irqfd support ...

> --
> error compiling committee.c: too many arguments to function