[PATCH v5 0/9] Error recovery for vfio-pci devices on s390x

Farhan Ali
2025-11-13T18:35:15Z

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
---------
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 error values for config space
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 | 37 +++++++++--
drivers/pci/pcie/aer.c | 3 +
drivers/pci/pcie/dpc.c | 3 +
drivers/pci/pcie/ptm.c | 3 +
drivers/pci/slot.c | 25 ++++++-
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 | 9 +++
drivers/vfio/pci/vfio_pci_zdev.c | 45 ++++++++++++-
include/linux/pci.h | 1 +
include/uapi/linux/vfio.h | 15 +++++
17 files changed, 321 insertions(+), 64 deletions(-)

--
2.43.0