[SRU][F][PATCH 0/1] zPCI DMA tables and bitmap leak on hard unplug (PCI Event 0x0304) (LP: 1896216)

[frank.heimes at canonical.com]

BugLink: https://bugs.launchpad.net/bugs/1896216

SRU Justification:

[Impact]

* Since zpci_dma_exit_device() is never called on a zPCI device there is a potential leaking in DMA tables and bitmaps.

* This is because commit "s390/pci: adapt events for zbus" removed the zpci_disable_device() call for a zPCI event with PEC 0x0304 (means on hot unplug).

* It is only not called on hot unplug with event type PEC 0x0304 - this is the one where Linux is informed the device is
gone instead of being asked to deconfigure it.

* It should also always leak them with that event type on an enabled device.

[Fix]

* afdf9550e54627fcf4dd609bdc1153059378cdf5 afdf9550e546 "s390/pci: fix leak of DMA tables on hard unplug"

[Test Case]

* Have an IBM Z LPAR, that has PCIe devices (like RoCE adapters) assigned and Ubuntu Server 20.04 installed.

* Disable and re-enable one (or more) of the assigned PCIe cards (using hotplug) - on LPAR this can be triggered using the 'Reassign I/O Path' function at the HMC/SE.

* Monitor DMA tables and bitmaps for any kind of leaking.

* Since these tables are vmalloc-ed memory, it's sufficient to monitor via /proc/meminfo and see that reassigning back and forth of a device will have the memory usage grow continuously.

* The test and verification needs to be conducted by IBM.

[Regression Potential]

* There regression risk can be considered as moderate, because:

* only a call of zpci_disable_device(zdev) got reintroduced (and some comment lines).

* Since __zpci_event_availability gets modified, the zPCI event handling could be scrud up,

* which could cause issues regarding the availability of zPCI devices

* and in worst case make zPCI devices unusable.

* But only one switch case of the function is modified and all cases break, so only PEC 0x0304 should be affected.

* And the code changes themselves are minimal, and the zPCI code is limited to the s390x architecture.

* On top test kernels were built and shared for further testing.

[Other]

* Since this commit needs to land in groovy too, but groovy is still in development (hence the SRU process does not apply for groovy yet), I've sent a separate Patch request for groovy.

Niklas Schnelle (1):
  From: Niklas Schnelle <schnelle at linux.ibm.com>

 arch/s390/pci/pci.c       | 4 ++++
 arch/s390/pci/pci_event.c | 2 ++
 2 files changed, 6 insertions(+)

-- 
2.25.1