Re: [PATCH v7 20/28] iommufd: Allow an input data_type via iommu_hw_info

Pranjal Shrivastava
2025-07-01T14:30:03Z

On Thu, Jun 26, 2025 at 12:34:51PM -0700, Nicolin Chen wrote:
> The iommu_hw_info can output via the out_data_type field the vendor data
> type from a driver, but this only allows driver to report one data type.
>
> Now, with SMMUv3 having a Tegra241 CMDQV implementation, it has two sets
> of types and data structs to report.
>
> One way to support that is to use the same type field bidirectionally.
>
> Reuse the same field by adding an "in_data_type", allowing user space to
> request for a specific type and to get the corresponding data.
>
> For backward compatibility, since the ioctl handler has never checked an
> input value, add an IOMMU_HW_INFO_FLAG_INPUT_TYPE to switch between the
> old output-only field and the new bidirectional field.
>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
> include/uapi/linux/iommufd.h | 20 +++++++++++++++++++-
> drivers/iommu/iommufd/device.c | 9 ++++++---
> 2 files changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
> index 6ad361ff9b06..6ae9d2102154 100644
> --- a/include/uapi/linux/iommufd.h
> +++ b/include/uapi/linux/iommufd.h
> @@ -628,6 +628,15 @@ enum iommufd_hw_capabilities {
> IOMMU_HW_CAP_PCI_PASID_PRIV = 1 << 2,
> };
>
> +/**
> + * enum iommufd_hw_info_flags - Flags for iommu_hw_info
> + * @IOMMU_HW_INFO_FLAG_INPUT_TYPE: If set, @in_data_type carries an input type
> + * for user space to request for a specific info
> + */
> +enum iommufd_hw_info_flags {
> + IOMMU_HW_INFO_FLAG_INPUT_TYPE = 1 << 0,
> +};
> +
> /**
> * struct iommu_hw_info - ioctl(IOMMU_GET_HW_INFO)
> * @size: sizeof(struct iommu_hw_info)
> @@ -637,6 +646,12 @@ enum iommufd_hw_capabilities {
> * data that kernel supports
> * @data_uptr: User pointer to a user-space buffer used by the kernel to fill
> * the iommu type specific hardware information data
> + * @in_data_type: This shares the same field with @out_data_type, making it be
> + * a bidirectional field. When IOMMU_HW_INFO_FLAG_INPUT_TYPE is
> + * set, an input type carried via this @in_data_type field will
> + * be valid, requesting for the info data to the given type. If
> + * IOMMU_HW_INFO_FLAG_INPUT_TYPE is unset, any input value will
> + * be seen as IOMMU_HW_INFO_TYPE_DEFAULT
> * @out_data_type: Output the iommu hardware info type as defined in the enum
> * iommu_hw_info_type.
> * @out_capabilities: Output the generic iommu capability info type as defined
> @@ -666,7 +681,10 @@ struct iommu_hw_info {
> __u32 dev_id;
> __u32 data_len;
> __aligned_u64 data_uptr;
> - __u32 out_data_type;
> + union {
> + __u32 in_data_type;
> + __u32 out_data_type;
> + };
> __u8 out_max_pasid_log2;
> __u8 __reserved[3];
> __aligned_u64 out_capabilities;
> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> index 64a51993e6a1..cbd86aabdd1c 100644
> --- a/drivers/iommu/iommufd/device.c
> +++ b/drivers/iommu/iommufd/device.c
> @@ -1506,6 +1506,7 @@ EXPORT_SYMBOL_NS_GPL(iommufd_access_rw, "IOMMUFD");
>
> int iommufd_get_hw_info(struct iommufd_ucmd *ucmd)
> {
> + const u32 SUPPORTED_FLAGS = IOMMU_HW_INFO_FLAG_INPUT_TYPE;
> struct iommu_hw_info *cmd = ucmd->cmd;
> void __user *user_ptr = u64_to_user_ptr(cmd->data_uptr);
> const struct iommu_ops *ops;
> @@ -1515,12 +1516,14 @@ int iommufd_get_hw_info(struct iommufd_ucmd *ucmd)
> void *data;
> int rc;
>
> - if (cmd->flags || cmd->__reserved[0] || cmd->__reserved[1] ||
> - cmd->__reserved[2])
> + if (cmd->flags & ~SUPPORTED_FLAGS)
> + return -EOPNOTSUPP;
> + if (cmd->__reserved[0] || cmd->__reserved[1] || cmd->__reserved[2])
> return -EOPNOTSUPP;
>
> /* Clear the type field since drivers don't support a random input */
> - cmd->out_data_type = IOMMU_HW_INFO_TYPE_DEFAULT;
> + if (!(cmd->flags & IOMMU_HW_INFO_FLAG_INPUT_TYPE))
> + cmd->in_data_type = IOMMU_HW_INFO_TYPE_DEFAULT;
>
> idev = iommufd_get_device(ucmd, cmd->dev_id);
> if (IS_ERR(idev))

Reviewed-by: Pranjal Shrivastava <praan@google.com>

> --
> 2.43.0
>