On 9/3/2026 10:55 AM, Farhan Ali wrote:
On 9/3/2026 2:19 AM, Cédric Le Goater wrote:
On 8/31/26 20:31, Farhan Ali wrote:
Hi,
This patch series introduces support for error recovery for
passthrough PCI
devices on System Z (s390x). This is the user space component for
the Linux
kernel patches [1]. The kernel patches were merged for 7.3 and it
had some
significant changes in VFIO API since the last QEMU series was
posted. But the
design for QEMU component is still the same.
For QEMU on eventfd notification for PCI error from vfio-pci driver
we call the
vfio error handler. We can use a per device error handler callback
to override
the default vfio error handler. For s390x specific error handler,
we retrieve
the architecture specific PCI error information and inject the
information into
the guest. Once the guest receives the error information, the guest
drivers will
drive the error recovery. Typically recovery involves a device
reset which
translate to CLP disable/enable cycle for the device.
I would appreciate some feedback on this patch series.
Hi Cedric,
Hi Farhan,
Have you seen Shameer's kernel series for PCI error recovery [1] ?
It uses a dedicated eventfd registered via VFIO_DEVICE_FEATURE_SET,
with a self-contained handler independent of the legacy err_notifier.
The QEMU side [2] just probes the feature, installs the eventfd, and
suppresses the legacy vm_stop path with a bool flag : no callback in
generic VFIO PCI code, which is cleaner.
This is also the pattern used by the other s390 VFIO devices: vfio-ccw
has three dedicated eventfds (io_notifier, crw_notifier, req_notifier)
and vfio-ap has two (req_notifier, cfg_notifier).
My thought process was to use the existing legacy err_notifier and let
each vfio-pci device handle the error. I thought the callback would
also provide some flexibility on each device handling the error.
I can take a look at Shameer's approach and see if its something we
can do. Just briefly looking at the QEMU code, it looks like it it
ties the eventfd to the generic vfio-pci code (of course this is in
flux). This would become problematic for s390x as unfortunately AER
recovery will not work for zPCI devices due to platform firmware being
involved in the recovery process.
For zPCI, it would mean extending VFIO_DEVICE_FEATURE_ZPCI_ERROR to
support SET with an eventfd field. The ABI is still new so the struct
can be extended, keeping the s390 error recovery code self-contained,
with no changes to generic VFIO PCI code. I think this approach is
preferable.
I would like to get some feedback from Alex to see if we could extend
the ABI.
I had been thinking about this a bit more, and I think having a another
eventfd for s390 to just notify on error would just be unnecessary
duplication. Because now we will have the legacy err_notifier + s390
error notifer eventfds for the same purpose but with different handlers.
Can we replace fd handler for the legacy err_notifier from
vfio_err_notifier_handler() to an s390 specific handler for s390
devices? This would also avoid any callback in the vfio core common code.
Thanks
Farhan
Thanks,
C.
[1]
https://lore.kernel.org/all/[email protected]/
[2]
https://github.com/shamiali2008/qemu-master/commit/e45458710cd8509fa5bd81f4376126b77b6f40be
