Re: granting access to MSI-X table and pending bit array

[Keir Fraser <keir.fraser@eu.citrix.com>]

On 09/07/2010 10:54, "Jan Beulich" <JBeulich@novell.com> wrote:

> With the revert mentioned above being about PV guests, I wonder
> what problems PV guests had with not being able to access the
> table and PBA ranges. Linux doesn't (so far) use the PBA at all,
> and according to my analysis of drivers/pci/msi-xen.c also doesn't
> access the table in any way even when being run privileged. Keir,
> with the description of c/s 20171 being rather brief - what was
> the problem PV guests were having? Or was that more specifically
> with stubdom wanting to do above mentioned writes on behalf of
> the serviced guest?

I was trying to pass through an Intel ixgbe VF to a PV guest. The guest
driver attempts to map some resource range (I think indicated via a BAR) and
that fails because one page in the range is disallowed, corresponding to an
MSI-X iomem page. Reverting this patch made things work. :-) Perhaps a dummy
page should get silently mapped in or something, but I didn't investigate
further myself.

 -- Keir