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 32.15.2). This invocation will activate the dual-monitor treatment of system-management interrupts (SMIs) and system-management mode (SMM) if it is not already active (see Section 32.15.6).

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
    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_SMM_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 32.15.2);
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 32.15.6.1)
    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 32.15.6.1);
            IF features field is invalid
                THEN
                    leave SMM;
                    VMfailValid(VMCALL with invalid SMM-monitor features);
                ELSE activate dual-monitor treatment of SMIs and SMM (see Section 32.15.6);
            FI;
        FI;
FI;

Flags Affected

See the operation section and Section 31.2.

Protected Mode Exceptions

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

This UNOFFICIAL, mechanically-separated, non-verified reference is provided for convenience, but it may be incomplete or broken in various obvious or non-obvious ways. Refer to Intel® 64 and IA-32 Architectures Software Developer’s Manual for anything serious.