[PATCH v12 0/7] 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 4) 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
---------
v11 series https://lore.kernel.org/all/20260316191544.2279-1-alifm@linux.ibm.com/
   - Address Bjorn's comments from v11 (patches 1-3).

   - Create a common function to check config space accessibility 
   (patch 2).

   - Address Alex's comments from v11 (patches 4, 5, 7).

   - Protect the mediated_recovery flag with the pending_errs_lock.
   Doing that it made sense to squash patches 5 and 6 from v11 
   (current patch 4). Even though the code didn't change significantly 
   I have dropped R-b tags for it. Would appreciate another look at the
   patch (current patch 4).

   - Dropped arch specific pcibios_resource_to_bus and
   pcibios_bus_to_resource as its not needed for this series. Will address
   the issue as a standalone patch separate from this series.

   - Rebased on pci/next, with head at f8a1c947ccc6 ("Merge branch 'pci/misc'") 


v10 series https://lore.kernel.org/all/20260302203325.3826-1-alifm@linux.ibm.com/
v10 -> v11
   - Rebase on pci/next to handle merge conflicts with patch 1.
   
   - Typo fixup in commit message (patch 4) and use guard() for mutex
    (patch 6).

v9 series https://lore.kernel.org/all/20260217182257.1582-1-alifm@linux.ibm.com/
v9 -> v10
   - Change pci_slot number to u16 (patch 1).

   - Avoid saving invalid config space state if config space is
   inaccessible in the device reset path. It uses the same patch as in v8
   with R-b from Niklas.

   - Rebase on 7.0.0-rc2


v8 series https://lore.kernel.org/all/20260122194437.1903-1-alifm@linux.ibm.com/
v8 -> v9
   - Avoid saving PCI config space state in reset path (patch 3) (suggested by Bjorn)
   
   - Add explicit version to struct vfio_device_feature_zpci_err (patch 7).

   - Rebase on 6.19


v7 series https://lore.kernel.org/all/20260107183217.1365-1-alifm@linux.ibm.com/
v7 -> v8
   - Rebase on 6.19-rc4

   - Address feedback from Niklas and Julien.


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 (7):
  PCI: Allow per function PCI slots to fix slot reset on s390
  PCI: Avoid saving config space state if inaccessible
  PCI: Fail FLR when config space is inaccessible
  s390/pci: Store PCI error information for passthrough devices
  vfio-pci/zdev: Add a device feature for error information
  vfio/pci: Add a reset_done callback for vfio-pci driver
  vfio/pci: Remove the pcie check for VFIO_PCI_ERR_IRQ_INDEX

 arch/s390/include/asm/pci.h       |  30 ++++++++
 arch/s390/pci/pci.c               |   1 +
 arch/s390/pci/pci_event.c         | 113 +++++++++++++++++-------------
 drivers/pci/hotplug/rpaphp_slot.c |   2 +-
 drivers/pci/pci.c                 |  32 ++++++++-
 drivers/pci/slot.c                |  33 ++++++---
 drivers/vfio/pci/vfio_pci_core.c  |  22 ++++--
 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               |   8 ++-
 include/uapi/linux/vfio.h         |  18 +++++
 12 files changed, 247 insertions(+), 69 deletions(-)

-- 
2.43.0