VMPTRLD

VMPTRLD is an assembly instruction in Intel’s VT-x virtualization set that loads the VMCS pointer from a memory operand into the processor’s current VMCS pointer. The VMCS (Virtual Machine Control Structure) contains the state and control information used for a VM’s execution, including guest and host state fields and VM-exit/entry controls. VMPTRLD effectively selects which VMCS region the CPU will reference for subsequent VMX operations.

When executed, VMPTRLD reads a 64-bit physical address from the specified memory operand and places that address into the VMCS pointer. The VMCS region at that address must be a valid, properly formatted VMCS region. In particular, the region must be 4 KB aligned and begin with the correct VMCS revision identifier. The instruction is a prerequisite for performing further VMX operations on that VMCS via VMREAD, VMWRITE, VMXON, VMXOFF, or VMPTRST.

Prerequisites and restrictions include that VMX operation must be active (the processor must be in VMX operation and the current task must have appropriate permissions to use VMX instructions). The VMCS pointer must refer to a region that is allocated for VMCS use and that conforms to VMX setup requirements. If these conditions are not met, the processor will generate a general protection fault.

Common outcomes include switching the active VMCS so subsequent VMX operations target the newly loaded VMCS. VMPTRLD is typically paired with VMPTRST, which stores the current VMCS pointer to memory, enabling management of multiple VMCS regions.

See also: VMPTRST, VMREAD, VMWRITE, VMX instruction set, VMCS.