Re: [PATCH v12 5/7] vfio-pci/zdev: Add a device feature for error information

[Farhan Ali]

On 3/31/2026 10:42 AM, Matthew Rosato wrote:
> On 3/30/26 1:40 PM, Farhan Ali wrote:
> > For zPCI devices, we have platform specific error information. The platform
> > firmware provides this error information to the operating system in an
> > architecture specific mechanism. To enable recovery from userspace for
> > these devices, we want to expose this error information to userspace. Add a
> > new device feature to expose this information.
> >
> > Signed-off-by: Farhan Ali <alifm@xxxxxxxxxxxxx>
> Reviewed-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
>
> Nits and a questions below
>
>
> > +int vfio_pci_zdev_feature_err(struct vfio_device *device, u32 flags,
> > +			      void __user *arg, size_t argsz)
> > +{
> > +	struct vfio_device_feature_zpci_err err = {};
> > +	struct vfio_pci_core_device *vdev;
> > +	struct zpci_dev *zdev;
> > +	int head = 0;
> > +	int ret;
> > +
> > +	vdev = container_of(device, struct vfio_pci_core_device, vdev);
> > +	zdev = to_zpci(vdev->pdev);
> > +	if (!zdev)
> > +		return -ENODEV;
> > +
> > +	ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_GET,
> > +				 sizeof(err));
> > +	if (ret != 1)
> > +		return ret;
> > +
> > +	mutex_lock(&zdev->pending_errs_lock);
> > +	if (zdev->pending_errs.count) {
> > +		head = zdev->pending_errs.head % ZPCI_ERR_PENDING_MAX;
> > +		err.pec = zdev->pending_errs.err[head].pec;
> > +		zdev->pending_errs.head++;
> > +		zdev->pending_errs.count--;
> > +		err.pending_errors = zdev->pending_errs.count;
> > +	}
> > +	mutex_unlock(&zdev->pending_errs_lock);
> > +
> Question: intentionally dropping so we don't hold over the copy_to_user?
>   That makes sense to me; but if not then may as well use guard(mutex)
> here too.  Does not affect my review tag.

Yes, exactly. I didn't see a need to hold the lock over copy_to_user().

Thanks

Farhan

> > +	err.version = 1;
> > +	if (copy_to_user(arg, &err, sizeof(err)))
> > +		return -EFAULT;
> > +
> > +	return 0;
> > +}
> > +
> >   int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
> >   {
> >   	struct zpci_dev *zdev = to_zpci(vdev->pdev);
> > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > index bb7b89330d35..2552eef42000 100644
> > --- a/include/uapi/linux/vfio.h
> > +++ b/include/uapi/linux/vfio.h
> > @@ -1510,6 +1510,24 @@ struct vfio_device_feature_dma_buf {
> >   	struct vfio_region_dma_range dma_ranges[] __counted_by(nr_ranges);
> >   };
> >   
> > +/**
> > + * VFIO_DEVICE_FEATURE_ZPCI_ERROR feature provides PCI error information to
> > + * userspace for vfio-pci devices on s390x. On s390x PCI error recovery
> 'On s390x, PCI error...' (suggest comma)
>
> > + * involves platform firmware and notification to operating system is done
> > + * by architecture specific mechanism. Exposing this information to
> > + * userspace allows userspace to take appropriate actions to handle an
> 'userspace allows it to take...' (reduce repetition of the word userspace)
>
> > + * error on the device. The pending_errors provide any additional errors
> > + * pending for the device, and userspace should read until zero.
> > + */
> > +
> > +struct vfio_device_feature_zpci_err {
> > +	__u8 version;
> > +	__u8 pending_errors;
> > +	__u16 pec;
> > +};
> > +
> > +#define VFIO_DEVICE_FEATURE_ZPCI_ERROR 12
> > +
> >   /* -------- API for Type1 VFIO IOMMU -------- */
> >   
> >   /**