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For virtualization cases the IDR/IIDR/AIDR values of the actual SMMU instance need to be available to the VMM so it can construct an appropriate vSMMUv3 that reflects the correct HW capabilities. For userspace page tables these values are required to constrain the valid values within the CD table and the IOPTEs. The kernel does not sanitize these values. If building a VMM then userspace is required to only forward bits into a VM that it knows it can implement. Some bits will also require a VMM to detect if appropriate kernel support is available such as for ATS and BTM. Start a new file and kconfig for the advanced iommufd support. This lets it be compiled out for kernels that are not intended to support virtualization, and allows distros to leave it disabled until they are shipping a matching qemu too. Tested-by: Nicolin Chen <nicolinc@nvidia.com> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com> Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com> Reviewed-by: Donald Dutile <ddutile@redhat.com> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> Link: https://lore.kernel.org/r/5-v4-9e99b76f3518+3a8-smmuv3_nesting_jgg@nvidia.com Signed-off-by: Will Deacon <will@kernel.org>