NASM 2.05 based x86 Instruction Reference[ch320]
A.5.295 SMINT, SMINTOLD: Software SMM Entry (CYRIX) SMINT ; 0F 38 [PENT,CYRIX] SMINTOLD ; 0F 7E [486,CYRIX] SMINT puts the processor into SMM mode. The CPU state information is saved in the SMM memory header, and then execution begins at the SMM base address. SMINTOLD is the same as SMINT, but was the opcode used on the 486. This pair of opcodes is specific to the Cyrix and compatible range of processors (Cyrix, IBM, Via).