On Tue, Apr 30, 2024 at 10:57:08PM +0800, Lu Baolu wrote: > /** > @@ -412,6 +415,9 @@ enum iommu_hwpt_data_type { > * @data_type: One of enum iommu_hwpt_data_type > * @data_len: Length of the type specific data > * @data_uptr: User pointer to the type specific data > + * @fault_id: The ID of IOMMUFD_FAULT object. Valid only if flags field of > + * IOMMU_HWPT_FAULT_ID_VALID is set. > + * @__reserved2: Padding to 64-bit alignment. Must be 0. > * > * Explicitly allocate a hardware page table object. This is the same object > * type that is returned by iommufd_device_attach() and represents the > @@ -442,6 +448,8 @@ struct iommu_hwpt_alloc { > __u32 data_type; > __u32 data_len; > __aligned_u64 data_uptr; > + __u32 fault_id; > + __u32 __reserved2; > }; > #define IOMMU_HWPT_ALLOC _IO(IOMMUFD_TYPE, IOMMUFD_CMD_HWPT_ALLOC) [..] > @@ -359,7 +359,7 @@ static const struct iommufd_ioctl_op iommufd_ioctl_ops[] = { > IOCTL_OP(IOMMU_GET_HW_INFO, iommufd_get_hw_info, struct iommu_hw_info, > __reserved), > IOCTL_OP(IOMMU_HWPT_ALLOC, iommufd_hwpt_alloc, struct iommu_hwpt_alloc, > - __reserved), > + __reserved2), This is now how the back compat mechanism works. The value here is the absolute minimum size, it should never increase. The first __reserved is always the right value. If you change it then old userspace that doesn't include the fault_id will stop working. Jason