Re: [PATCH v5 7/9] iommufd: Associate fault object with iommufd_hw_pgtable

Jason Gunthorpe
2024-05-08T00:25:09Z

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