Re: [RFC PATCH v13 4/4] s390: implementing CHSC SEI for AP config change

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 6/26/25 12:19 PM, Matthew Rosato wrote:
> On 6/9/25 12:44 PM, Rorie Reyes wrote:
>> Handle interception of the CHSC SEI instruction for requests
>> indicating the guest's AP configuration has changed.
>>
>> If configuring --without-default-devices, hw/s390x/ap-stub.c
>> was created to handle such circumstance. Also added the
>> following to hw/s390x/meson.build if CONFIG_VFIO_AP is
>> false, it will use the stub file.
>>
>> Signed-off-by: Rorie Reyes <rreyes@linux.ibm.com>
>> Reviewed-by: Anthony Krowiak <akrowiak@linux.ibm.com>
>> Reviewed-by: Cédric Le Goater <clg@redhat.com>
> 
> FYI, this patch (or some part of this series) breaks hotplug for PCI devices on s390x.  I verified it breaks with both PCI passthrough and virtio-pci via virsh attach-device.
> 

I was unaware of 639ff87a1a ("attribute constructor for cfg_chg_events_lock") which apparently was already sitting in vfio-next and merged to master the day after I reported this issue.

FWIW, 639ff87a1a resolves the issue by ensuring the mutex_init happens even if there is no vfio-ap device attached so long as vfio_ap is configured/built (and I like the use of the constructor).

I also now see the stub functions in hw/s390x/ap-stub.c that will be called if vfio_ap is not configured.

So: my concerns are resolved.  Thanks!