[PATCH v7 0/9] Error recovery for vfio-pci devices on s390x

[Farhan Ali <alifm@linux.ibm.com>]

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.

This is how a typical flow for passthrough devices to a VM would work:
For passthrough devices to a VM, the driver bound to the device on the host 
is vfio-pci. vfio-pci driver does support the error_detected() callback 
(vfio_pci_core_aer_err_detected()), and on an PCI error s390x recovery 
code on the host will call the vfio-pci error_detected() callback. The 
vfio-pci error_detected() callback will notify userspace/QEMU via an 
eventfd, and return PCI_ERS_RESULT_CAN_RECOVER. At this point the s390x 
error recovery on the host will skip any further action(see patch 6) and 
let userspace drive the error recovery.

Once userspace/QEMU is notified, it then injects this error into the VM 
so device drivers in the VM can take recovery actions. For example for a 
passthrough NVMe device, the VM's OS NVMe driver will access the device. 
At this point the VM's NVMe driver's error_detected() will drive the 
recovery by returning PCI_ERS_RESULT_NEED_RESET, and the s390x error 
recovery in the VM's OS will try to do a reset. Resets are privileged 
operations and so the VM will need intervention from QEMU to perform the 
reset. QEMU will invoke the VFIO_DEVICE_RESET ioctl to now notify the 
host that the VM is requesting a reset of the device. The vfio-pci driver 
on the host will then perform the reset on the device to recover it.


Thanks
Farhan

ChangeLog
---------
v6 series https://lore.kernel.org/all/2c609e61-1861-4bf3-b019-a11c137d26a5@linux.ibm.com/
v6 -> v7
    - Rebase on 6.19-rc4

    - Update commit message based on Niklas's suggestion (patch 3).

v5 series https://lore.kernel.org/all/20251113183502.2388-1-alifm@linux.ibm.com/
v5 -> v6
   - Rebase on 6.18 + Lukas's PCI: Universal error recoverability of
   devices series (https://lore.kernel.org/all/cover.1763483367.git.lukas@wunner.de/)

   - Re-work config space accessibility check to pci_dev_save_and_disable() (patch 3).
   This avoids saving the config space, in the reset path, if the device's config space is
   corrupted or inaccessible.

v4 series https://lore.kernel.org/all/20250924171628.826-1-alifm@linux.ibm.com/
v4 -> v5
    - Rebase on 6.18-rc5

    - Move bug fixes to the beginning of the series (patch 1 and 2). These patches
    were posted as a separate fixes series 
https://lore.kernel.org/all/a14936ac-47d6-461b-816f-0fd66f869b0f@linux.ibm.com/

    - Add matching pci_put_dev() for pci_get_slot() (patch 6).

v3 series https://lore.kernel.org/all/20250911183307.1910-1-alifm@linux.ibm.com/
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@linux.ibm.com/
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@linux.ibm.com/
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 (9):
  PCI: Allow per function PCI slots
  s390/pci: Add architecture specific resource/bus address translation
  PCI: Avoid saving config space state if inaccessible
  PCI: Add additional checks for flr reset
  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       |  29 ++++++++
 arch/s390/pci/pci.c               |  75 +++++++++++++++++++++
 arch/s390/pci/pci_event.c         | 107 +++++++++++++++++-------------
 drivers/pci/host-bridge.c         |   4 +-
 drivers/pci/pci.c                 |  19 +++++-
 drivers/pci/slot.c                |  25 ++++++-
 drivers/vfio/pci/vfio_pci_core.c  |  20 ++++--
 drivers/vfio/pci/vfio_pci_intrs.c |   3 +-
 drivers/vfio/pci/vfio_pci_priv.h  |   9 +++
 drivers/vfio/pci/vfio_pci_zdev.c  |  45 ++++++++++++-
 include/linux/pci.h               |   1 +
 include/uapi/linux/vfio.h         |  16 +++++
 12 files changed, 292 insertions(+), 61 deletions(-)

-- 
2.43.0