RE: [PATCH v2 3/4] iommufd: Add IOMMU_DEVICE_GET_HW_INFO

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Liu, Yi L <yi.l.liu@intel.com>
> Sent: Thursday, March 9, 2023 3:54 PM
> +
> +int iommufd_device_get_hw_info(struct iommufd_ucmd *ucmd)
> +{
> +	struct iommu_hw_info *cmd = ucmd->cmd;
> +	struct iommufd_device *idev;
> +	const struct iommu_ops *ops;
> +	void *data;
> +	unsigned int length, data_len;
> +	int rc;
> +
> +	if (cmd->flags || cmd->__reserved || !cmd->data_len)
> +		return -EOPNOTSUPP;
> +
> +	idev = iommufd_get_device(ucmd, cmd->dev_id);
> +	if (IS_ERR(idev))
> +		return PTR_ERR(idev);
> +
> +	ops = dev_iommu_ops(idev->dev);
> +	if (!ops || !ops->hw_info) {
> +		rc = -EOPNOTSUPP;
> +		goto out_put;
> +	}
> +
> +	/* driver has hw_info callback should have a unique driver_type */
> +	if (WARN_ON(ops->driver_type ==
> IOMMU_HW_INFO_TYPE_DEFAULT)) {
> +		rc = -EOPNOTSUPP;
> +		goto out_put;
> +	}

ok, here is where the check is done.

> +
> +	data = ops->hw_info(idev->dev, &data_len);

if we directly return type in @hw_info, this becomes:

	data = ops->hw_info(idev->dev, &data_len, &driver_type);

> +/**
> + * struct iommu_hw_info - ioctl(IOMMU_DEVICE_GET_HW_INFO)
> + * @size: sizeof(struct iommu_hw_info)
> + * @flags: Must be 0
> + * @dev_id: The device being attached to the iommufd

"The device bound to the iommufd"

> + * @data_len: Input the length of the user buffer in bytes. Output the
> + *            length of data filled to the user buffer.

s/to/in/

> + * @data_ptr: Pointer to the type specific structure

"Pointer to the user buffer"

> + * @out_data_type: Output the iommu hardware info type, it is one of
> + *                 enum iommu_hw_info_type.

s/it is one of/as defined by/

> + * @__reserved: Must be 0
> + *
> + * Query the hardware iommu information for given device which has been
> + * bound to iommufd. @data_len is the size of the buffer which captures
> + * iommu type specific data and the data will be filled. Trailing bytes
> + * are zeroed if the user buffer is larger than the data kernel has.
> + *
> + * The type specific data would be used to sync capability between the
> + * vIOMMU and the hardware IOMMU. e.g. nested translation requires to

s/vIOMMU/virtual IOMMU/

> + * check the hardware IOMMU capability, since a stage-1 translation table
> + * is owned by user but used by hardware IOMMU.

"check ... capability so guest stage-1 page table uses a format compatible
to the hardware IOMMU"

> + *
> + * The @out_data_type will be filled if the ioctl succeeds. It would
> + * be used to decode the data filled in the buffer pointed by @data_ptr.
> + *
> + * This is only available for the physical devices bound to iommufd as
> + * only physical devices can have hardware IOMMU.

not required. User doesn't know whether it's physical or emulated
device.