A processor comprising: a core cache comprising a non-persistent authenticated code module, ACM, wherein the ACM is a processor-authenticated firmware module and is configured to be executed out of a protected environment created in the processor core cache, and to load a persistent SEAM loader module in a second subrange of a reserved range of a system memory to be coupled to the processor that is defined in a range register; and the persistent SEAM loader module is configured to install or update a SEAM TDX module in a first subrange of the reserved range, the SEAM TDX module to initiate a secure arbitration mode, SEAM, of the processor and to create, manage and invoke trust domains; a decoder comprising circuitry to decode a secure arbitration mode call instruction, SEAMCALL, based on an instruction set, the SEAMCALL instruction comprising: a first field to provide an opcode to indicate that a logical processor is to transition from a legacy Virtual Machines Extension root operation; and a second field to provide an operand to specify one of: the persistent SEAM loader module loaded in the second subrange of the reserved range by the ACM and to install or update the SEAM TDX module in the first subrange of the reserved range; or the SEAM TDX module to be loaded in the first subrange of the reserved range by the persistent SEAM loader module and to initiate the SEAMof the processor; and execution circuitry, coupled to the decoder, to execute the SEAMCALL instruction, wherein the execution circuitry is to determine whether to access the one of the persistent SEAM loader module or the SEAM TDX module based on the operand. a core cache comprising a non-persistent authenticated code module, ACM, wherein the ACM is a processor-authenticated firmware module and is configured to be executed out of a protected environment created in the processor core cache, and to load a persistent SEAM loader module in a second subrange of a reserved range of a system memory to be coupled to the processor that is defined in a range register; and the persistent SEAM loader module is configured to install or update a SEAM TDX module in a first subrange of the reserved range, the SEAM TDX module to initiate a secure arbitration mode, SEAM, of the processor and to create, manage and invoke trust domains; the ACM is a processor-authenticated firmware module and is configured to be executed out of a protected environment created in the processor core cache, and to load a persistent SEAM loader module in a second subrange of a reserved range of a system memory to be coupled to the processor that is defined in a range register; and to be executed out of a protected environment created in the processor core cache, and to load a persistent SEAM loader module in a second subrange of a reserved range of a system memory to be coupled to the processor that is defined in a range register; and the persistent SEAM loader module is configured to install or update a SEAM TDX module in a first subrange of the reserved range, the SEAM TDX module to initiate a secure arbitration mode, SEAM, of the processor and to create, manage and invoke trust domains; a decoder comprising circuitry to decode a secure arbitration mode call instruction, SEAMCALL, based on an instruction set, the SEAMCALL instruction comprising: a first field to provide an opcode to indicate that a logical processor is to transition from a legacy Virtual Machines Extension root operation; and a second field to provide an operand to specify one of: the persistent SEAM loader module loaded in the second subrange of the reserved range by the ACM and to install or update the SEAM TDX module in the first subrange of the reserved range; or the SEAM TDX module to be loaded in the first subrange of the reserved range by the persistent SEAM loader module and to initiate the SEAMof the processor; and a first field to provide an opcode to indicate that a logical processor is to transition from a legacy Virtual Machines Extension root operation; and a second field to provide an operand to specify one of: the persistent SEAM loader module loaded in the second subrange of the reserved range by the ACM and to install or update the SEAM TDX module in the first subrange of the reserved range; or the SEAM TDX module to be loaded in the first subrange of the reserved range by the persistent SEAM loader module and to initiate the SEAMof the processor; and the persistent SEAM loader module loaded in the second subrange of the reserved range by the ACM and to install or update the SEAM TDX module in the first subrange of the reserved range; or the SEAM TDX module to be loaded in the first subrange of the reserved range by the persistent SEAM loader module and to initiate the SEAMof the processor; and execution circuitry, coupled to the decoder, to execute the SEAMCALL instruction, wherein the execution circuitry is to determine whether to access the one of the persistent SEAM loader module or the SEAM TDX module based on the operand.