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
---------
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         |  15 +++++
 12 files changed, 291 insertions(+), 61 deletions(-)

-- 
2.43.0

Hi Bjorn,

Polite ping, to see if there are any concerns with this patch series 
(more specifically patches 1-4).

Thanks

Farhan

On 12/1/2025 2:08 PM, Farhan Ali wrote:
> 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
> ---------
> 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         |  15 +++++
>   12 files changed, 291 insertions(+), 61 deletions(-)
>