Re: kvm PCI assignment & VFIO ramblings

On Mon, 2011-08-01 at 10:40 -0600, Alex Williamson wrote:

On Sun, 2011-07-31 at 08:21 +1000, Benjamin Herrenschmidt wrote:

quoted

On Sat, 2011-07-30 at 09:58 +1000, Benjamin Herrenschmidt wrote:

quoted

Hi folks !

So I promised Anthony I would try to summarize some of the comments &
issues we have vs. VFIO after we've tried to use it for PCI pass-through
on POWER. It's pretty long, there are various items with more or less
impact, some of it is easily fixable, some are API issues, and we'll
probably want to discuss them separately, but for now here's a brain
dump.

David, Alexei, please make sure I haven't missed anything :-)

And I think I have :-)

  * Config space

VFIO currently handles that as a byte stream. It's quite gross to be
honest and it's not right. You shouldn't lose access size information
between guest and host when performing real accesses.

Some config space registers can have side effects and not respecting
access sizes can be nasty.

It's a bug, let's fix it.

Right. I was just trying to be exhaustive :-) If you don't beat us to
it, we'll eventually submit patches to fix it, we haven't fixed it yet
either, just something I noticed (because this byte-transport also makes
handling of endianess clumsly).

Cheers,
Ben.