Re: [Qemu-devel] vfio with iommu groups

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Sun, 2012-05-13 at 22:16 -0600, Alex Williamson wrote:
> > However theoretically we might want to show these 3 PCIe bridges as well (but not the root complex).
> > For example, INTx lines should be swizzled when the guest parses a device tree and
> > tries to calculate a real IRQ number. VFIO does not handles bridges at all, it treats them as PCI
> > functions.
> > 
> > Is there any idea what to do with bridges?
> 
> I don't really have a problem with the idea of exposing bridges, but it
> get's pretty complicated.  What happens if the guest reprograms the
> subordinate bus numbers?  Is there any advantage vs exposing an emulated
> bridge in it's place?  Do you have a proposal for it?  Thanks,

I think exposing an emulated bridge would be more in the "spirit" of the
current vfio and safer for now (long run, as we already discussed, we
might look at an other option with more direct HW access for power).

We do want to expose those bridges one way or another for the sake of
getting the interrupt routing right, since the guest will make
assumptions based on those bridges to calculate the proper swizzling.

Cheers,
Ben.