Re: [PATCH v16 4/7] s390/pci: Store PCI error information for passthrough devices

[Niklas Schnelle]

On Thu, 2026-05-14 at 11:00 -0700, Farhan Ali wrote:
> For a passthrough device we need co-operation from user space to recover
> the device. This would require to bubble up any error information to user
> space.  Let's store this error information for passthrough devices, so it
> can be retrieved later.
> 
> We can now have userspace drivers (vfio-pci based) on s390x. The userspace
> drivers will not have any KVM fd and so no kzdev associated with them. So
> we need to update the logic for detecting passthrough devices to not depend
> on struct kvm_zdev.
> 
> Reviewed-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> Signed-off-by: Farhan Ali <alifm@xxxxxxxxxxxxx>
> ---
>  arch/s390/include/asm/pci.h      |  30 ++++++++
>  arch/s390/pci/pci.c              |   1 +
>  arch/s390/pci/pci_event.c        | 114 +++++++++++++++++--------------
>  drivers/vfio/pci/vfio_pci_zdev.c |  18 ++++-
>  4 files changed, 109 insertions(+), 54 deletions(-)
> 
--- snip ---
> @@ -216,12 +223,23 @@ static pci_ers_result_t zpci_event_attempt_error_recovery(struct pci_dev *pdev)
>  		goto out_unlock;
>  	}
>  
> +	mediated_recovery = zpci_store_pci_error(pdev, ccdf) == 0 ? true : false;
> +

This incorrectly treats it as not-mediated recovery when the queue runs
full and zpci_store_pci_error() returns -ENOMEM (Sashiko also noticed
this though the explanation is a bit hard to read).

>  	ers_res = zpci_event_notify_error_detected(pdev, driver);
>  	if (ers_result_indicates_abort(ers_res)) {
>  		status_str = "failed (abort on detection)";
>  		goto out_unlock;
>  	}
>  
> +	if (mediated_recovery) {
> +		pr_info("%s: Leaving recovery of pass-through device to user-space\n",
> +			pci_name(pdev));
> +		ers_res = PCI_ERS_RESULT_RECOVERED;
> +		status_str = "in progress";
> +		mutex_unlock(&zdev->pending_errs_lock);

The unlock here seems like a bad leftover from the previous code.
You're not holding that lock here. (Also found by Sashiko).

> +		goto out_unlock;
> +	}
> +
--- snip ---