Unified address translation for virtualization of input/output devices

Embodiments of apparatuses, methods, and systems for unified address translation for virtualization of input/output devices are described. In an embodiment, an apparatus includes first circuitry to use at least an identifier of a device to locate a context entry and second circuitry to use at least a process address space identifier (PASID) to locate a PASID-entry. The context entry is to include at least one of a page-table pointer to a page-table translation structure and a PASID. The PASID-entry is to include at least one of a first-level page-table pointer to a first-level translation structure and a second-level page-table pointer to a second-level translation structure. The PASID is to be supplied by the device. At least one of the apparatus, the context entry, and the PASID entry is to include one or more control fields to indicate whether the first-level page-table pointer or the second-level page-table pointer is to be used.