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Henk-Jan Lebbink edited this page Jun 4, 2026 · 1 revision

VMX INSTRUCTION REFERENCE VMCALL — Call to VM Monitor

Opcode/ Instruction Op/En Description
0F 01 C1 VMCALL ZO Call to VM monitor by causing VM exit.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
ZO NA NA NA NA

Description

This instruction allows guest software can make a call for service into an underlying VM monitor. The details of the programming interface for such calls are VMM-specific; this instruction does nothing more than cause a VM exit, registering the appropriate exit reason.

Use of this instruction in VMX root operation invokes an SMM monitor (see Section 34.15.2). This invocation will acti-vate the dual-monitor treatment of system-management interrupts (SMIs) and system-management mode (SMM) if it is not already active (see Section 34.15.6).

Operation

IF not in VMX operation
    THEN #UD;
ELSIF in VMX non-root operation
    THEN VM exit;
ELSIF (RFLAGS.VM = 1) or (IA32_EFER.LMA = 1 and CS.L = 0)
    THEN #UD;
ELSIF CPL > 0 or in SEAM root operation
    THEN #GP(0);
ELSIF in SMM or the logical processor does not support the dual-monitor treatment of SMIs and SMM or the valid bit in the IA32_SM-M_MONITOR_CTL MSR is clear
    THEN VMfail (VMCALL executed in VMX root operation);
ELSIF dual-monitor treatment of SMIs and SMM is active
    THEN perform an SMM VM exit (see Section 34.15.2);
ELSIF current-VMCS pointer is not valid
    THEN VMfailInvalid;
ELSIF launch state of current VMCS is not clear
    THEN VMfailValid(VMCALL with non-clear VMCS);
ELSIF VM-exit control fields are not valid (see Section 34.15.6.1)
    THEN VMfailValid (VMCALL with invalid VM-exit control fields);
ELSE
    enter SMM;
    read revision identifier in MSEG;
    IF revision identifier does not match that supported by processor
        THEN
            leave SMM;
            VMfailValid(VMCALL with incorrect MSEG revision identifier);
        ELSE
            read SMM-monitor features field in MSEG (see Section 34.15.6.1);
            IF features field is invalid
                THEN
                    leave SMM;
                            33-9 Vol. 3C
VMX INSTRUCTION REFERENCE
                    VMfailValid(VMCALL with invalid SMM-monitor features);
                ELSE activate dual-monitor treatment of SMIs and SMM (see Section 34.15.6);
            FI;
        FI;
FI;

Flags Affected

See the operation section and Section 33.2.

Protected Mode Exceptions

#GP(0) If the current privilege level is not 0 and the logical processor is in VMX root operation. If in SEAM root operation.

#UD If executed outside VMX operation.

Real-Address Mode Exceptions

#UD If executed outside VMX operation.

Virtual-8086 Mode Exceptions

#UD If executed outside VMX non-root operation.

Compatibility Mode Exceptions

#UD If executed outside VMX non-root operation.

64-Bit Mode Exceptions

#UD If executed outside VMX operation.

33-10 Vol. 3C

Source: Intel® 64 and IA-32 Architectures Software Developer's Manual, Combined Volumes (Order Number 325462-091US, March 2026)
Generated: 7-6-2026

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