Error recovery for vfio-pci devices on s390x

Hi,

This Linux kernel patch series introduces support for error recovery for
passthrough PCI devices on System Z (s390x). 

Background
----------
For PCI devices on s390x an operating system receives platform specific
error events from firmware rather than through AER.Today for
passthrough/userspace devices, we don't attempt any error recovery and
ignore any error events for the devices. The passthrough/userspace devices
are managed by the vfio-pci driver. The driver does register error handling
callbacks (error_detected), and on an error trigger an eventfd to
userspace.  But we need a mechanism to notify userspace
(QEMU/guest/userspace drivers) about the error event. 

Proposal
--------
We can expose this error information (currently only the PCI Error Code)
via a device feature. Userspace can then obtain the error information 
via VFIO_DEVICE_FEATURE ioctl and take appropriate actions such as driving 
a device reset.

I would appreciate some feedback on this series. Part of the series touches
PCI common code, so would like to get some feedback on those patches.

Thanks
Farhan

ChangeLog
---------
v3 series https://lore.kernel.org/all/20250911183307.1910-1-alifm@l...
v3 -> v4
    - Remove warn messages for each PCI capability not restored (patch 1)

    - Check PCI_COMMAND and PCI_STATUS register for error value instead of device id 
    (patch 1)

    - Fix kernel crash in patch 3

    - Added reviewed by tags

    - Address comments from Niklas's (patches 4, 5, 7)

    - Fix compilation error non s390x system (patch 8)

    - Explicitly align struct vfio_device_feature_zpci_err (patch 8)


v2 series https://lore.kernel.org/all/20250825171226.1602-1-alifm@l...
v2 -> v3
   - Patch 1 avoids saving any config space state if the device is in error
   (suggested by Alex)

   - Patch 2 adds additional check only for FLR reset to try other function 
     reset method (suggested by Alex).

   - Patch 3 fixes a bug in s390 for resetting PCI devices with multiple
     functions. Creates a new flag pci_slot to allow per function slot.

   - Patch 4 fixes a bug in s390 for resource to bus address translation.

   - Rebase on 6.17-rc5


v1 series https://lore.kernel.org/all/20250813170821.1115-1-alifm@l...
v1 - > v2
   - Patches 1 and 2 adds some additional checks for FLR/PM reset to 
     try other function reset method (suggested by Alex).

   - Patch 3 fixes a bug in s390 for resetting PCI devices with multiple
     functions.

   - Patch 7 adds a new device feature for zPCI devices for the VFIO_DEVICE_FEATURE 
     ioctl. The ioctl is used by userspace to retriece any PCI error
     information for the device (suggested by Alex).

   - Patch 8 adds a reset_done() callback for the vfio-pci driver, to
     restore the state of the device after a reset.

   - Patch 9 removes the pcie check for triggering VFIO_PCI_ERR_IRQ_INDEX.


Farhan Ali (10):
  PCI: Avoid saving error values for config space
  PCI: Add additional checks for flr reset
  PCI: Allow per function PCI slots
  s390/pci: Add architecture specific resource/bus address translation
  s390/pci: Restore IRQ unconditionally for the zPCI device
  s390/pci: Update the logic for detecting passthrough device
  s390/pci: Store PCI error information for passthrough devices
  vfio-pci/zdev: Add a device feature for error information
  vfio: Add a reset_done callback for vfio-pci driver
  vfio: Remove the pcie check for VFIO_PCI_ERR_IRQ_INDEX

 arch/s390/include/asm/pci.h        |  30 +++++++-
 arch/s390/pci/pci.c                |  75 ++++++++++++++++++++
 arch/s390/pci/pci_event.c          | 107 ++++++++++++++++-------------
 arch/s390/pci/pci_irq.c            |   9 +--
 drivers/pci/host-bridge.c          |   4 +-
 drivers/pci/hotplug/s390_pci_hpc.c |  10 ++-
 drivers/pci/pci.c                  |  37 ++++++++--
 drivers/pci/pcie/aer.c             |   3 +
 drivers/pci/pcie/dpc.c             |   3 +
 drivers/pci/pcie/ptm.c             |   3 +
 drivers/pci/slot.c                 |  14 +++-
 drivers/pci/tph.c                  |   3 +
 drivers/pci/vc.c                   |   3 +
 drivers/vfio/pci/vfio_pci_core.c   |  20 ++++--
 drivers/vfio/pci/vfio_pci_intrs.c  |   3 +-
 drivers/vfio/pci/vfio_pci_priv.h   |   8 +++
 drivers/vfio/pci/vfio_pci_zdev.c   |  45 +++++++++++-
 include/linux/pci.h                |   1 +
 include/uapi/linux/vfio.h          |  15 ++++
 19 files changed, 318 insertions(+), 75 deletions(-)

-- 
2.43.0