Re: kvm PCI assignment & VFIO ramblings

Alex Williamson
2011-08-02T18:35:19Z

On Tue, 2011-08-02 at 12:14 -0600, Alex Williamson wrote:
> On Tue, 2011-08-02 at 18:28 +1000, David Gibson wrote:
> > On Sat, Jul 30, 2011 at 12:20:08PM -0600, Alex Williamson wrote:
> > > On Sat, 2011-07-30 at 09:58 +1000, Benjamin Herrenschmidt wrote:
> > [snip]
> > > On x86, the USB controllers don't typically live behind a PCIe-to-PCI
> > > bridge, so don't suffer the source identifier problem, but they do often
> > > share an interrupt. But even then, we can count on most modern devices
> > > supporting PCI2.3, and thus the DisINTx feature, which allows us to
> > > share interrupts. In any case, yes, it's more rare but we need to know
> > > how to handle devices behind PCI bridges. However I disagree that we
> > > need to assign all the devices behind such a bridge to the guest.
> > > There's a difference between removing the device from the host and
> > > exposing the device to the guest.
> >
> > I think you're arguing only over details of what words to use for
> > what, rather than anything of substance here. The point is that an
> > entire partitionable group must be assigned to "host" (in which case
> > kernel drivers may bind to it) or to a particular guest partition (or
> > at least to a single UID on the host). Which of the assigned devices
> > the partition actually uses is another matter of course, as is at
> > exactly which level they become "de-exposed" if you don't want to use
> > all of then.
>
> Well first we need to define what a partitionable group is, whether it's
> based on hardware requirements or user policy. And while I agree that
> we need unique ownership of a partition, I disagree that qemu is
> necessarily the owner of the entire partition vs individual devices.

Sorry, I didn't intend to have such circular logic. "... I disagree
that qemu is necessarily the owner of the entire partition vs granted
access to devices within the partition". Thanks,

Alex