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

[Matthew Rosato]

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.

> +	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 -------- */
>  
>  /**