Re: [PATCH v14 0/7] Error recovery for vfio-pci devices on s390x

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

Gentle ping on this series.


Thanks

Farhan


On 4/21/2026 9:30 AM, 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 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
> ---------
> v13 series https://lore.kernel.org/all/20260413210608.2912-1-alifm@linux.ibm.com/
> v13 -> v14
>     - Remove version from vfio uAPI struct. Instead reserve additional space
>     and add a flags field. The flags will be used to indicate any usage of
>     the reserved space (patch 5).
>
>     - Remove pending_errors from vfio uAPI struct and instead return an
>     error to indicate no more pending error for userspace to handle (patch 5).
>
>     - Rebase on recent linux master
>
> v12 series https://lore.kernel.org/all/20260330174011.1161-1-alifm@linux.ibm.com/
> v12 -> v13
>     - Add the mediated_recovery flag as part of struct zpci_ccdf_pending
>     and protect the struct with pending_errs_lock (patch 4).
>
>     - Move dequeing pending error logic to a helper function (patch 5).
>
>     - Update device feature number for VFIO_DEVICE_FEATURE_ZPCI_ERROR (patch 5).
>
>     - Rebase on linux-next with tag next-20260410
>
>
> 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       |  32 +++++++
>   arch/s390/pci/pci.c               |   1 +
>   arch/s390/pci/pci_event.c         | 136 +++++++++++++++++++-----------
>   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  |  48 ++++++++++-
>   include/linux/pci.h               |   8 +-
>   include/uapi/linux/vfio.h         |  29 +++++++
>   12 files changed, 282 insertions(+), 73 deletions(-)
>