Vol. 3C 30-9

VMX INSTRUCTION REFERENCE

VMCALL—Call to VM Monitor

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 
activate 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

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 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 34.15.6.2);
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 34.15.6);

FI;

FI;

FI;

Opcode

Instruction

Description

0F 01 C1

VMCALL

Call to VM monitor by causing VM exit.