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Hello all,

I recently discovered that the kernel config generated by
tools/packaging/kernel has CONFIG_PCI_MMCONFIG disabled.  That's
probably not a good idea, since that's a very atypical config for
modern systems, and for complicated reasons it completely stops SHPC
hotplug from working.

So, I've filed
https://github.com/kata-containers/kata-containers/pull/2311 to change
it.

But..

I have reason to suspect that anyone using Kata's VFIO support is
actually *relying* on this bogus guest behaviour to make things work.
In all my experiements when I try to use VFIO devices with a more
normal kernel, the device is detected in the guest after the agent's
rescan and works, but only briefly.  When the SHPC hotplug completes
5s later, this interferes somehow and puts the device in a badly
broken state (config space accesses fail completely)[0].

To make things harder, seeing how this affects the CI is also non-trivial:
  1) Changing the config in the kata-containers repo will not (AFAICT)
     trigger a rebuild of the cached guest kernel in the CI, and so it
     will be tested effectively without the change.
  2) The vfio CI testcase is pretty rudimentary.  I think it's quite
     likely it could complete fast enough to succeed and shut down
     before the SHPC hotplug completes and breaks the device

At this point I'm inclined to just push the change anyway and deal
with the fallout as and when it occurs.  But does any one have a
better idea?


[0] In fact, if disable_idle_d3=N for the vfio-pci module, it even
    puts the device into a broken state in the *host*, requiring a
    host reboot to restore.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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