[SRU][O][PATCH 0/1] [Ubuntu 25.04] s390/pci: Fix PCHID per port multi-function detection (LP: #2104120)

[Massimiliano Pellizzer]

BugLink: https://bugs.launchpad.net/bugs/2104120

[Impact]

Description: s390/pci: Fix PCHID per port multi-function detection

Symptom: There are two cases in which PCI functions are incorrectly
               placed, or not placed, in a shared PCI topology. In the first
               case a PCI physical function (PF) which is initially in standby
               was incorrectly not creating a new PCI topology when hotplugged,
               but would if configured during boot. In the second case a PCI
               virtual function (VF) would be placed in the shared PCI topology
               of a PF if that PF is from the same card even if the parent PF
               is not in the configuration which should lead the VF to be
               isolated in its own single function topology.

Problem: Both problems are caused by logic bugs in the determination of
               which PCI functions create topologies and when a PCI function
               may be added to an existing topology.

[Fix]

Cherry pick from mainline of:
- dc287e4c9149 s390/pci: Fix SR-IOV for PFs initially in standby
- 05793884a1f3 s390/pci: Pull search for parent PF out of pci_iov_setup_virtfn()
- 2844ddbd540f s390/pci: Fix handling of isolated VFs

[Test Plan]

Fix tested by IBM.

[Where problems could occur]

The fix affects SR-IOV support in the s390x PCI subsystem.
A user might experience issues like missing or misconfigured VFs,
failed VF passthrough to guests, sysfs inconsistencies, or degraded I/O performance.


[Other Info]

The three commits mentioned above have been already included in Noble.