Intel Extensible Firmware Interface Specification page 111

A virtual address map may only be applied one time. Once the runtime system is in virtual mode,
calls to this function return EFI_UNSUPPORTED.
Status Codes Returned
EFI_SUCCESS
EFI_UNSUPPORTED
EFI_INVALID_PARAMETER
EFI_NO_MAPPING
EFI_NOT_FOUND
Version 1.02
The virtual address map has been applied.
EFI firmware is not at runtime, or the EFI firmware is already in
virtual address mapped mode.
DescriptorSize DescriptorVersion
or
invalid.
A virtual address was not supplied for a range in the memory
map that requires a mapping.
A virtual address was supplied for an address that is not found
in the memory map.
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