Passthrough

configname: CONFIG_IOMMU_DEFAULT_PASSTHROUGH

IOMMU default domain type
└─>Passthrough
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Trusted devices are identity-mapped, giving them unrestricted access
to memory with minimal performance overhead. Equivalent to passing
"iommu.passthrough=1" (historically "iommu=pt") on the command line.

If this mode is not supported by the IOMMU driver, the effective
runtime default will fall back to IOMMU_DEFAULT_DMA_STRICT.