RE: [PATCH v8 11/15] iommufd/viommu: Select vIOMMU operations before allocation

[Tian, Kevin]

> From: Aneesh Kumar K.V (Arm) <aneesh.kumar@xxxxxxxxxx>
> Sent: Thursday, November 5, 2026 12:16 AM
> 
> Physical IOMMU drivers currently provide the vIOMMU size and
> initialization callbacks through iommu_ops. The initialization callback
> then selects and installs the corresponding iommufd_viommu_ops.
> 
> Add iommu_ops::get_viommu_ops() to select the operations from the
> physical device and requested vIOMMU type before allocation. Move the
> size and initialization callbacks into iommufd_viommu_ops. The core can
> then validate the selected operations, allocate the driver structure,
> initialize it, and install the operations.
> 
> Convert AMD, Arm SMMUv3, Tegra CMDQV, and the selftest backend to the
> new interface.
> 
> Selecting the operations early allows subsequent changes to use
> implementation-specific vIOMMU properties, including when validating the
> parent HWPT.

what does "implementation-specific" mean? Isn't every existing vIOMMU
type already implementation specific?

> 
>  /*
>   * This function is assigned to struct
> iommufd_viommu_ops.alloc_domain_nested()
> - * during the call to struct iommu_ops.viommu_init().
> + * when the vIOMMU operations are selected.
>   */
>  struct iommu_domain *
>  amd_iommu_alloc_domain_nested(struct iommufd_viommu *viommu, u32
> flags,

the comment sounds changing the semantics.

ideally it's still assigned at viommu_init(), just from iommufd_viommu_ops
instead of iommu_ops now.