Re: [PATCH v2 0/3] s390x/pci: fix ISM reset

["Cédric Le Goater" <clg@redhat.com>]

On 1/18/24 19:51, Matthew Rosato wrote:
> Commit ef1535901a0 (re-)introduced an issue where passthrough ISM devices
> on s390x would enter an error state after reboot.  This was previously fixed
> by 03451953c79e, using device reset callbacks, however the change in
> ef1535901a0 effectively triggers a cold reset of the pci bus before the
> device reset callbacks are triggered.
> 
> To resolve this, this series proposes to remove the use of the reset callback
> for ISM cleanup and instead trigger ISM reset from subsystem_reset before
> triggering bus resets.  This has to happen before the bus resets because the
> reset of s390-pcihost will trigger reset of the PCI bus followed by the
> s390-pci bus, and the former will trigger vfio-pci reset / the aperture-wide
> unmap that ISM gets upset about.
>   
>    /s390-pcihost (s390-pcihost)
>      /pci.0 (PCI)
>      /s390-pcibus.0 (s390-pcibus)
>      
> While fixing this, it was also noted that kernel warnings could be seen that
> indicate a guest ISC reference count error.  That's because in some reset
> cases we were not bothering to disable AIF, but would again re-enable it after
> the reset (causing the reference count to grow erroneously).  This was a base
> issue that went unnoticed because the kernel previously did not detect and
> issue a warning for this scenario.
> 
> 
> Changes for v2:
> - Fold a typo fix from patch 2 into patch 1 where it belongs
> - Add block comment re: timing of ISM reset
> - Add review tags


Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.