RE: [PATCH v8 3/5] iommufd: Add IOMMU_GET_HW_INFO

From: Liu, Yi L yi.l.liu@intel.com Sent: Wednesday, August 16, 2023 8:14 PM

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 need to be compatible 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_GET_HW_INFO ioctl to query the IOMMU hardware information (a.k.a capability) for a given device. The returned data is vendor specific, userspace needs to decode it with the structure by the output @out_data_type field.

"The format of the returned data is vendor specific and must be decoded according to @out_data_type field".

+int iommufd_get_hw_info(struct iommufd_ucmd *ucmd) +{

• struct iommu_hw_info *cmd = ucmd->cmd;
• void __user *user_ptr = u64_to_user_ptr(cmd->data_uptr);
• const struct iommu_ops *ops;
• struct iommufd_device *idev;
• unsigned int data_len;
• unsigned int copy_len;
• void *data = NULL;
• int rc;
• if (cmd->flags || cmd->__reserved)

• 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) {

• data = ops->hw_info(idev->dev, &data_len, &cmd-
  

...

out_data_type);

• if (IS_ERR(data)) {
  

• 	rc = PTR_ERR(data);
  

• 	goto err_put;
  

• }
  

• /*
  

•  * drivers that have hw_info callback should have a unique
  

•  * iommu_hw_info_type.
  

•  */
  

• if (WARN_ON_ONCE(cmd->out_data_type ==
  

• 		 IOMMU_HW_INFO_TYPE_NONE)) {
  

• 	rc = -ENODEV;
  

• 	goto out;
  

• }
  

• } else {

• cmd->out_data_type = IOMMU_HW_INFO_TYPE_NONE;
  

• data_len = 0;
  

• data = NULL;
  

data is already initialized as NULL.

• /*

• * We return the length the kernel supports so userspace may know
  

what

• * the kernel capability is. It could be larger than the input buffer.
  

• */
  

• cmd->data_len = data_len;
• rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));

+out:

out_free:

• kfree(data);

+err_put:

out_put: (since this is also used in the success path)

• • To capture an iommu type specific hardware information data,

@data_uptr and

• • its length @data_len must be provided. Trailing bytes will be zeroed if the
• • user buffer is larger than the data that kernel has. Otherwise, kernel only
• • fills the buffer using the given length in @data_len. If the ioctl succeeds,
• • @data_len will be updated to the length that kernel actually supports,
• • @out_data_type will be filled to decode the data filled in the buffer
• • pointed by @data_uptr. Input @data_len == zero is allowed, no

information

• • data will be filled to user, but user space could get the

iommu_hw_info_type

• • filled in @out_data_type and the iommu hardware information data

length

• • supported by kernel filled in @data_len.

I'd just keep "Input @data_len == zero is allowed" and remove all the trailing words which just duplicate with the former context.

Reviewed-by: Kevin Tian kevin.tian@intel.com