[Pkg-libvirt-maintainers] Bug#1107536: Bug#1107536: PPC64LE: Device hotplug/unplug requires guest reboot

[Trupti]

On 2025-06-20 23:59, Andrea Bolognani wrote:
> On Wed, Jun 18, 2025 at 01:58:39AM +0530, Trupti wrote:
>> On 2025-06-10 12:29, Trupti wrote:
>> > On 2025-06-09 23:38, Andrea Bolognani wrote:
>> > > Honestly this sounds like a guest OS issue rather than a bug in
>> > > libvirt. Is any message produced in dmesg/journal as a consequence of
>> > > the hotplug operation?
>> >
>> > The guest dmesg shows the RTAS hot-plug signal, but no further messages
>> > appear.
>> 
>> Hello,
>> 
>> I have a key update from further testing.
>> 
>> Libvirt appears to be working correctly, as the VM's live XML is 
>> updated
>> immediately after an attach-interface command.
>> 
>> The main finding comes from the guest kernel log. It reveals that both
>> attach-interface and detach-interface cause the guest to receive the 
>> exact
>> same signal: RTAS Hotplug Event (229).
>> 
>> Receiving the same signal for both adding and removing a device is the
>> probable cause of the hotplug failure.
> 
> More evidence that the issue is on the guest OS side, not the libvirt
> side. I'm strongly inclined to close this bug at this point. Let me
> know if you disagree, otherwise I'll go ahead.
> 
> Did you try using the virtio model? You didn't clarify whether this
> additional testing is still happening with rtl8139, which I wouldn't
> necessarily expect to work correctly for ppc64le.

Thank you for your observations.

You were absolutely right in suggesting earlier that the issue could be 
on the guest OS side.
Based on internal discussions and validation across various 
distributions with similar configurations, I can confirm that the root 
cause lies in the guest kernel and not in libvirt.

Specifically, the guest kernel was expecting the device tree property 
ibm,drc-info for PCI hotplug support, but in this case, only the older 
property ibm,drc-indexes was present. Since ibm,drc-info was missing, 
the kernel failed to handle the hotplug operation correctly.

This upstream patch fixes the issue by allowing the kernel to use 
ibm,drc-indexes when ibm,drc-info is not found:
https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/commit/?h=next&id=41a1452759a8b1121df9cf7310acf31d766ba70b

I’ll loop in the Debian kernel team to check if this patch can be 
considered for inclusion in the Trixie kernel. I’ll also test the patch 
and share results once available.

I’ll also validate the virtio model setup and update accordingly.


Thanks,
Trupti.