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

[Baolu Lu <baolu.lu@linux.intel.com>]

On 5/11/23 10:30 PM, Yi Liu wrote:
> Under nested IOMMU translation, userspace owns the stage-1 translation
> table (e.g. the stage-1 page table of Intel VT-d or the context table
> of ARM SMMUv3, and etc.). Stage-1 translation tables are vendor specific,
> and needs to be compatiable with the underlying IOMMU hardware. Hence,
> userspace should know the IOMMU hardware capability before creating and
> configuring the stage-1 translation table to kernel.
> 
> This adds IOMMU_DEVICE_GET_HW_INFO to query the IOMMU hardware information
> for a given device. The returned data is vendor specific, userspace needs
> to decode it with the structure mapped by the @out_data_type field.
> 
> As only physical devices have IOMMU hardware, so this will return error
> if the given device is not a physical device.
> 
> Co-developed-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>   drivers/iommu/iommufd/device.c          | 72 +++++++++++++++++++++++++
>   drivers/iommu/iommufd/iommufd_private.h |  1 +
>   drivers/iommu/iommufd/main.c            |  3 ++
>   include/uapi/linux/iommufd.h            | 37 +++++++++++++
>   4 files changed, 113 insertions(+)
> 
> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> index 051bd8e99858..bc99d092de8f 100644
> --- a/drivers/iommu/iommufd/device.c
> +++ b/drivers/iommu/iommufd/device.c
> @@ -263,6 +263,78 @@ u32 iommufd_device_to_id(struct iommufd_device *idev)
>   }
>   EXPORT_SYMBOL_NS_GPL(iommufd_device_to_id, IOMMUFD);
>   
> +static int iommufd_zero_fill_user(u64 ptr, int bytes)
> +{
> +	int index = 0;
> +
> +	for (; index < bytes; index++) {
> +		if (put_user(0, (uint8_t __user *)u64_to_user_ptr(ptr + index)))
> +			return -EFAULT;
> +	}
> +	return 0;
> +}
> +
> +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;

If the iommu driver doesn't provide a hw_info callback, it still
returns success?

> +
> +	/* 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;
> +	}
> +
> +	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));
> +
> +out_err:
> +	kfree(data);
> +	iommufd_put_object(&idev->obj);
> +	return rc;
> +}
> +
>   static int iommufd_group_setup_msi(struct iommufd_group *igroup,
>   				   struct iommufd_hw_pagetable *hwpt)
>   {

Best regards,
baolu