Open Stack

On Mon, Jul 26, 2021 at 07:44:34PM +1000, David Gibson wrote:
> 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

So, I realized I was misunderstanding how the config_version stuff
works.  Once I fix that up, I can trigger a guest kernel rebuild
easily enough.

.. and it does indeed fail, specifically when it tries to shut down
the Kata VM, which is interesting.


> 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.
> 



> _______________________________________________
> kata-dev mailing list
> kata-dev at lists.katacontainers.io
> http://lists.katacontainers.io/cgi-bin/mailman/listinfo/kata-dev


-- 
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
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: not available
URL: <http://lists.katacontainers.io/pipermail/kata-dev/attachments/20210727/34730b78/attachment.sig>