[vfio-users] ACS and IOMMU groups on Skylake/Sunrise

[Alex Williamson]

On Wed, 18 Apr 2018 15:39:16 -0600
Alex Williamson <alex.williamson at redhat.com> wrote:
> On Wed, 18 Apr 2018 17:20:51 -0400
> Philip Kania <philip.kania at onshape.com> wrote:
> > 
> > I expected that, with the quirks, by VF would appear in its own group. Any
> > idea what I'm missing?  
> 
> Can't really tell what your hierarchy is here, are you suggesting you
> have an ASMedia PCI bridge sitting between your root port and the
> I350?  That seems unlikely, although it'd explain the grouping.  Please
> provide full 'sudo lspci -vvv' output and
> 'find /sys/kernel/iommu_groups/ -type l'.  Thanks,

<info provided offline>

Your I350 at 09:00.{0,1} is directly downstream of the root port at
00:1c.4 (the ASMedia bridge is not relevant):

00:1c.4 PCI bridge: Intel Corporation Sunrise Point-H PCI Express Root Port
  Bus: primary=00, secondary=09, subordinate=09, sec-latency=0

However, the ACS quirks for this chipset are based on the fact that ACS
is implemented by the root ports, it's just not exactly to spec, using
dword registers rather than word sized registers.  On your system, not
even this broken ACS implementation is listed in the extended
capabilities, only AER and the Secondary PCIe capabilities are listed.
Intel chips often have ways to disable chipset features in the BIOS and
I'd guess this is such a case.  Therefore unless you can find a BIOS
option or new BIOS revision to expose the ACS capability, the quirks we
have for this chipset won't help you.  Thanks,

Alex