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Message-ID: <2c609e61-1861-4bf3-b019-a11c137d26a5@linux.ibm.com>
Date: Tue, 9 Dec 2025 12:13:42 -0800
From: Farhan Ali <alifm@...ux.ibm.com>
To: linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-pci@...r.kernel.org, Bjorn Helgaas <helgaas@...nel.org>
Cc: lukas@...ner.de, alex@...zbot.org, clg@...hat.com, stable@...r.kernel.org,
schnelle@...ux.ibm.com, mjrosato@...ux.ibm.com
Subject: Re: [PATCH v6 0/9] Error recovery for vfio-pci devices on s390x
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(-)
>
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