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Privileged instructions

    Privileged instructions that affect system data structures can
    only be executed when the CPL is zero. If the processor finds one
    of these instructions when CPL > 0, it signals a general
    protection exception:

        CLTS              Clear Task-Switched Flag
        HLT               Halt the Processor
        LGDT              Load Global Descriptor Table Reg.
        LIDT              Load Interrupt Descriptor Table Reg.
        LLDT              Load Local Descriptor Table Reg.
        LMSW              Load Machine Status Word
        LTR               Load Task Register
        MOV to/from CRn   Move to/from Control Register
        MOV to/from DRn   Move to/from Debug Register
        MOV to/from TRn   Move to/from Test Register
        and
        special instructions related to system management (INVD,
        INVLPG, WBINVD, WRMSR a.o.)