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

Alex Williamson
2010-10-20T14:58:41Z

On Wed, 2010-10-20 at 15:43 +0200, Michael S. Tsirkin wrote:
> On Wed, Oct 20, 2010 at 12:59:42PM +0200, Avi Kivity wrote:
> > 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.
>
> Some issues off the top of my head are
> - readonly/virtualized table correctness
> hopefully will start converging now that
> we are switching to standard registers from pci_regs.h
> - work out some capability negotiation mechanism so userspace/kernel
> can detect bug fixes/missing features and recover or fail gracefully
> - with multiple assigned devices in a guest:
> I don't think we have figured out how do they share an iommu context

A single UIOMMU fd can be used for multiple devices. The code I wrote
supports this, but it's really only meant to support a uiommufd passed
via the command line for libvirt usage. Since libvirt doesn't yet
support vfio, it's never been tested.

> - maybe: reset handling (flr support) - need to look a it

I'd add that for the qemu vfio driver, we need to work out the KVM
interrupt optimizations, otherwise we suffer extra latency vs current
code.

>
> > On the other hand, changes to the old infrastructure are much
> > more amenable to backporting for long term support distro kernels,
> > so we may need to actively develop both for a while.

Yep, I think we'll need to continue development and probably maintain
them both for a while.

Alex