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

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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@xxxxxxxxxx>
Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
---
  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



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