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

[Farhan Ali <alifm@linux.ibm.com>]

On 4/7/2026 8:53 AM, Alex Williamson wrote:
> On Mon, 30 Mar 2026 10:40:09 -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        | 18 ++++++++++++++++
>>   4 files changed, 65 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..647a9e8f348d 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 -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 0658095ac5b1..0a8663879eee 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);
> Inconsistent that this isn't a helper exported from the previous patch.

Do you prefer it to be in a helper function? I can move it to a helper 
function.

>
> What's the meaning of err.pec = 0?  Could this be interpreted as an
> error itself?

An err.pec = 0 would indicate there are no pending errors. I don't think 
anything would prevent userspace from doing a VFIO_DEVICE_FEATURE_GET 
even if not nudged by an eventfd?


>
>> +
>> +	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
>> + * 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. 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
> 12 is used in linux-next by the PRECOPY_INFOv2 feature.  Thanks,
>
> Alex

Ah okay, will update this. I think my next rebase would be on the new 
kernel (7.1) and that should have the conflicting PCI patches.

Thanks

Farhan

>> +
>>   /* -------- API for Type1 VFIO IOMMU -------- */
>>   
>>   /**