APPARATUS AND METHOD FOR MANAGING UNSUPPORTED INSTRUCTION SET ARCHITECTURE (ISA) FEATURES IN A VIRTUALIZED ENVIRONMENT

An apparatus and method for supporting deprecated instructions. For example, one embodiment of a processor comprises: A processor comprising: a plurality of cores, each core comprising a current microarchitecture to execute instructions and process data, the current microarchitecture including hardware support for virtual execution environment comprising a hypervisor running at a first privilege level and one or more virtual machines each running at a second privilege level, the microarchitecture further including partial hardware support for executing deprecated instructions associated with a prior microarchitecture; at least one core of the plurality of cores comprising: a decoder to decode the instructions, the decoder to specify one or more microoperations corresponding to each of the instructions; execution circuitry to execute the corresponding microoperations; wherein either a first type or a second type of virtual machine exit is to be performed responsive to detecting a deprecated instruction in a first virtual machine, wherein responsive to the first type of virtual machine exit, the hypervisor is to perform a first emulation of the prior microarchitecture without reliance on the partial hardware support, and wherein responsive to the second type of virtual machine exit, the hypervisor is to perform a second emulation of the prior microarchitecture relying on the partial hardware support.