RE: [PATCH v3 3/4] iommufd: Add IOMMU_DEVICE_GET_HW_INFO

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Sent: Thursday, May 11, 2023 10:30 PM
> +
> +int iommufd_device_get_hw_info(struct iommufd_ucmd *ucmd)
> +{
> +	struct iommu_hw_info *cmd = ucmd->cmd;
> +	unsigned int length = 0, data_len;
> +	struct iommufd_device *idev;
> +	const struct iommu_ops *ops;
> +	void *data = NULL;
> +	int rc = 0;
> +
> +	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->hw_info)
> +		goto done;
> +
> +	/* driver has hw_info callback should have a unique hw_info_type */
> +	if (ops->hw_info_type == IOMMU_HW_INFO_TYPE_NONE) {
> +		pr_warn_ratelimited("iommu driver set an invalid type\n");
> +		rc = -ENODEV;
> +		goto out_err;
> +	}

this should be a WARN_ON_ONCE() since it's a driver bug.

> +
> +	data = ops->hw_info(idev->dev, &data_len);
> +	if (IS_ERR(data)) {
> +		rc = PTR_ERR(data);
> +		goto out_err;
> +	}
> +
> +	length = min(cmd->data_len, data_len);
> +	if (copy_to_user(u64_to_user_ptr(cmd->data_ptr), data, length)) {
> +		rc = -EFAULT;
> +		goto out_err;
> +	}
> +
> +	/*
> +	 * Zero the trailing bytes if the user buffer is bigger than the
> +	 * data size kernel actually has.
> +	 */
> +	if (length < cmd->data_len) {
> +		rc = iommufd_zero_fill_user(cmd->data_ptr + length,
> +					    cmd->data_len - length);
> +		if (rc)
> +			goto out_err;
> +	}
> +
> +done:
> +	cmd->data_len = length;
> +	cmd->out_data_type = ops->hw_info_type;
> +	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));

the 'done' label should be moved before above zero_fill. Otherwise
in !ops->hw_info case the user buffer is not cleared.

>  union ucmd_buffer {
>  	struct iommu_destroy destroy;
>  	struct iommu_hwpt_alloc hwpt;
> +	struct iommu_hw_info info;

follow alphabetic order this should be ahead of hwpt.

> @@ -302,6 +303,8 @@ static const struct iommufd_ioctl_op
> iommufd_ioctl_ops[] = {
>  	IOCTL_OP(IOMMU_DESTROY, iommufd_destroy, struct
> iommu_destroy, id),
>  	IOCTL_OP(IOMMU_HWPT_ALLOC, iommufd_hwpt_alloc, struct
> iommu_hwpt_alloc,
>  		 __reserved),
> +	IOCTL_OP(IOMMU_DEVICE_GET_HW_INFO,
> iommufd_device_get_hw_info,
> +		 struct iommu_hw_info, __reserved),

before IOMMU_HWPT_ALLOC

> +
> +/**
> + * struct iommu_hw_info - ioctl(IOMMU_DEVICE_GET_HW_INFO)
> + * @size: sizeof(struct iommu_hw_info)
> + * @flags: Must be 0
> + * @dev_id: The device bound to the iommufd
> + * @data_len: Input the length of the user buffer in bytes. Output the
> + *            length of data filled in the user buffer.
> + * @data_ptr: Pointer to the user buffer
> + * @out_data_type: Output the iommu hardware info type as defined by
> + *                 enum iommu_hw_info_type.
> + * @__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
> + * virtual IOMMU and the hardware IOMMU. e.g. nested translation
> requires
> + * to check the hardware IOMMU 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.
> + */
> +struct iommu_hw_info {
> +	__u32 size;
> +	__u32 flags;
> +	__u32 dev_id;
> +	__u32 data_len;
> +	__aligned_u64 data_ptr;
> +	__u32 out_data_type;
> +	__u32 __reserved;

it's unusual to have reserved field in the end. It makes more sense
to move data_ptr to the end to make it meaningful.

> +};
> +#define IOMMU_DEVICE_GET_HW_INFO _IO(IOMMUFD_TYPE,
> IOMMUFD_CMD_DEVICE_GET_HW_INFO)
>  #endif

Here we have a naming confusion.

'IOMMU' is the prefix of iommufd ioctls.

'DEVICE' is the subjective.

Then "GET_HW_INFO" implies getting hardware info related to
this device. then it should not be restricted to the iommu info.

with that it's clearer to call it IOMMU_DEVICE_GET_IOMMU_INFO.

similarly for struct iommu_hw_info.

'iommu' is the prefix for all iommufd ioctl structures.

then 'hw_info' is too broard.

iommu_device_iommu_info reads better? though having two
iommu's in the name is a little bit annoying...