vmcall

Call to VM Monitor

VMCALL

Guest VM calls the Hypervisor (VM Exit).

Details

Initiates a VM exit from guest mode to invoke the VM monitor (hypervisor). The instruction immediately transitions control to the hypervisor and is available only when running in VMX non-root mode; execution in root mode raises #UD. RFLAGS.CF and ZF may be set on VM exit depending on the exit reason; other flags are preserved across the transition.

Pseudocode Operation

if (CPL != 0 || VMX_ROOT == 1) raise #UD
VMEXIT(VMCALL_EXIT_REASON)
if (exit_error) { RFLAGS.CF ← 1; RFLAGS.ZF ← 1; }

Example

VMCALL

Encoding

Binary Layout

Format VMX

Opcode 0F 01 C1

Extension VMX

Operands

Reference (Intel® SDM)

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
0F 01 C1	VMCALL	ZO			Call to VM monitor by causing VM exit.

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 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;


VMCALL—Call to VM Monitor                                                                                          33-9  Vol. 3C


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.

Exceptions

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.