A method, computer program product, and distributed data processing system that allows a single physical I/O adapter, such as a PCI, PCI-X, or PCI-E adapter, to validate that a direct memory access address referenced by an incoming I/O transaction that was initiated through a memory mapped I/O operation are associated with a virtual adapter or virtual resource that is referenced by the incoming memory mapped I/O operation is provided. Specifically, the present invention is directed to a mechanism for sharing conventional PCI (Peripheral Component Interconnect) I/O adapters, PCI-X I/O Adapters, PCI-Express I/O Adapters, and, in general, any I/O adapter that uses a memory mapped I/O interface for communications. A single physical I/O adapter validates that one or more direct memory access addresses referenced by an incoming I/O transaction initiated through a memory mapped I/O operation are associated with a virtual adapter or virtual resource that is referenced by the incoming memory mapped I/O operation.