On Thu, Nov 13, 2014 at 05:43:14PM +0000, Daniel P. Berrange wrote:
> On Thu, Nov 13, 2014 at 09:36:18AM -0800, Dan Smith wrote:
> > > That sounds like something worth exploring at least, I didn't know
> > > about that kernel build option until now :-) It sounds like it ought
> > > to be enough to let us test the NUMA topology handling, CPU pinning
> > > and probably huge pages too.
> > 
> > Okay. I've been vaguely referring to this as a potential test vector,
> > but only just now looked up the details. That's my bad :)
> > 
> > > The main gap I'd see is NUMA aware PCI device assignment since the
> > > PCI <-> NUMA node mapping data comes from the BIOS and it does not
> > > look like this is fakeable as is.
> > 
> > Yeah, although I'd expect that the data is parsed and returned by a
> > library or utility that may be a hook for fakeification. However, it may
> > very well be more trouble than it's worth.
> > 
> > I still feel like we should be able to test generic PCI in a similar way
> > (passing something like a USB controller through to the guest, etc).
> > However, I'm willing to believe that the intersection of PCI and NUMA is
> > a higher order complication :)
> 
> Oh I forgot to mention with PCI device assignment (as well as having a
> bunch of PCI devices available[1]), the key requirement is an IOMMU.
> AFAIK, neither Xen or KVM provide any IOMMU emulation, so I think we're
> out of luck for even basic PCI assignment testing inside VMs.

Ok, turns out that wasn't entirely accurate in general.

KVM *can* emulate an IOMMU, but it requires that the guest be booted
with the q35 machine type, instead of the ancient PIIX4 machine type,
and also QEMU must be launched with "-machine iommu=on". We can't do
this in Nova, so although it is theoretically possible, it is not
doable for us in reality :-(

Regards,
Daniel
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