Intel 64 and IA-32 Architectures Software Developers Manual Volume 2B, Instruction Set Reference, N-Z

Vol. 2B 5-1
CHAPTER 5
VMX INSTRUCTION REFERENCE
5.1 OVERVIEW
This chapter describes the virtual-machine extensions (VMX) for the Intel 64 and
IA-32 architectures. VMX is intended to support virtualization of processor hardware
and a system software layer acting as a host to multiple guest software environ-
ments. The virtual-machine extensions (VMX) includes five instructions that manage
the virtual-machine control structure (VMCS) and five instruction that manage VMX
operation. Additional details of VMX are described in IA-32 Intel Architecture Soft-
ware Developer’s Manual, Volume 3B.
The behavior of the VMCS-maintenance instructions is summarized below:
• VMPTRLD — This instruction takes a single 64-bit source operand that is in
memory. It makes the referenced VMCS active and current, loading the current-
VMCS pointer with this operand and establishes the current VMCS based on the
contents of VMCS-data area in the referenced VMCS region. Because this makes
the referenced VMCS active, a logical processor may start maintaining on the
processor some of the VMCS data for the VMCS.
• VMPTRST — This instruction takes a single 64-bit destination operand that is in
memory. The current-VMCS pointer is stored into the destination operand.
• VMCLEAR — This instruction takes a single 64-bit operand that is in memory.
The instruction sets the launch state of the VMCS referenced by the operand to
“clear”, renders that VMCS inactive, and ensures that data for the VMCS have
been written to the VMCS-data area in the referenced VMCS region. If the
operand is the same as the current-VMCS pointer, that pointer is made invalid.
• VMREAD — This instruction reads a component from the VMCS (the encoding of
that field is given in a register operand) and stores it into a destination operand
that may be a register or in memory.
• VMWRITE — This instruction writes a component to the VMCS (the encoding of
that field is given in a register operand) from a source operand that may be a
register or in memory.
The behavior of the VMX management instructions is summarized below:
• VMCALL — This instruction allows a guest in VMX non-root operation to call the
VMM for service. A VM exit occurs, transferring control to the VMM.
• VMLAUNCH — This instruction launches a virtual machine managed by the
VMCS. A VM entry occurs, transferring control to the VM.
• VMRESUME — This instruction resumes a virtual machine managed by the
VMCS. A VM entry occurs, transferring control to the VM.
• VMXOFF — This instruction causes the processor to leave VMX operation.