VMXOFF — Leave VMX Operation

Description ¶

Takes the logical processor out of VMX operation, unblocks INIT signals, conditionally re-enables A20M, and clears any address-range monitoring.⁷

Operation ¶

IF (not in VMX operation) or (CR0.PE = 0) or (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
    THEN #UD;
ELSIF in VMX non-root operation
    THEN VMexit;
ELSIF CPL > 0
    THEN #GP(0);
ELSIF dual-monitor treatment of SMIs and SMM is active
    THEN VMfail(VMXOFF under dual-monitor treatment of SMIs and SMM);
    ELSE
        leave VMX operation;
        unblock INIT;
        IF IA32_SMM_MONITOR_CTL[2] = 08
            THEN unblock SMIs;
        IF outside SMX operation9
            THEN unblock and enable A20M;
        FI;
        clear address-range monitoring;
        VMsucceed;
FI;

Flags Affected ¶

See the operation section and Section 30.2.

Protected Mode Exceptions ¶

Real-Address Mode Exceptions ¶

Virtual-8086 Mode Exceptions ¶

7. See the information on MONITOR/MWAIT in Chapter 8, “Multiple-Processor Management,” of the Intel^® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A.

8. Setting IA32_SMM_MONITOR_CTL[bit 2] to 1 prevents VMXOFF from unblocking SMIs regardless of the value of the register’s value bit (bit 0). Not all processors allow this bit to be set to 1. Software should consult the VMX capability MSR IA32_VMX_MISC (see Appendix A.6) to determine whether this is allowed.

9. A logical processor is outside SMX operation if GETSEC[SENTER] has not been executed or if GETSEC[SEXIT] was executed after the last execution of GETSEC[SENTER]. See Chapter 6, “Safer Mode Extensions Reference.”

Compatibility Mode Exceptions ¶

64-Bit Mode Exceptions ¶