Re: [PATCH v11 7/9] vfio-pci/zdev: Add a device feature for error information

[Alex Williamson <alex@shazbot.org>]

On Mon, 16 Mar 2026 12:15:42 -0700
Farhan Ali <alifm@linux.ibm.com> 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@linux.ibm.com>
> ---
>  drivers/vfio/pci/vfio_pci_core.c |  2 ++
>  drivers/vfio/pci/vfio_pci_priv.h |  9 ++++++++
>  drivers/vfio/pci/vfio_pci_zdev.c | 36 ++++++++++++++++++++++++++++++++
>  include/uapi/linux/vfio.h        | 17 +++++++++++++++
>  4 files changed, 64 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index d43745fe4c84..bbdb625e35ef 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -1534,6 +1534,8 @@ int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
>  		return vfio_pci_core_feature_token(vdev, flags, arg, argsz);
>  	case VFIO_DEVICE_FEATURE_DMA_BUF:
>  		return vfio_pci_core_feature_dma_buf(vdev, flags, arg, argsz);
> +	case VFIO_DEVICE_FEATURE_ZPCI_ERROR:
> +		return vfio_pci_zdev_feature_err(device, flags, arg, argsz);
>  	default:
>  		return -ENOTTY;
>  	}
> diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
> index 27ac280f00b9..eed69926d8a1 100644
> --- a/drivers/vfio/pci/vfio_pci_priv.h
> +++ b/drivers/vfio/pci/vfio_pci_priv.h
> @@ -89,6 +89,8 @@ int vfio_pci_info_zdev_add_caps(struct vfio_pci_core_device *vdev,
>  				struct vfio_info_cap *caps);
>  int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev);
>  void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev);
> +int vfio_pci_zdev_feature_err(struct vfio_device *device, u32 flags,
> +			      void __user *arg, size_t argsz);
>  #else
>  static inline int vfio_pci_info_zdev_add_caps(struct vfio_pci_core_device *vdev,
>  					      struct vfio_info_cap *caps)
> @@ -103,6 +105,13 @@ static inline int vfio_pci_zdev_open_device(struct vfio_pci_core_device *vdev)
>  
>  static inline void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>  {}
> +
> +static inline int vfio_pci_zdev_feature_err(struct vfio_device *device,
> +					    u32 flags, void __user *arg,
> +					    size_t argsz)
> +{
> +	return -ENODEV;

-ENOTTY

> +}
>  #endif
>  
>  static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
> index 2be37eab9279..d2748dd67c55 100644
> --- a/drivers/vfio/pci/vfio_pci_zdev.c
> +++ b/drivers/vfio/pci/vfio_pci_zdev.c
> @@ -141,6 +141,42 @@ int vfio_pci_info_zdev_add_caps(struct vfio_pci_core_device *vdev,
>  	return ret;
>  }
>  
> +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);
> +
> +	err.version = 1;

Returns uninitialized kernel data for case where there are no pending
errors, initialize err with = {};

> +	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..21b1473e4779 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -1510,6 +1510,23 @@ 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 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 error on the
> + * device.

This should include some explicit discussion of how pending_errors in
interpreted, ie. pending _additional_ errors, userspace should read
until zero.  Thanks,

Alex

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