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VMM(4) Device Drivers Manual (amd64) VMM(4)

vmmvirtual machine monitor

vmm0 at mainbus0

#include <machine/vmmvar.h>

The vmm driver implements a virtual machine monitor (VMM) suitable for executing (VMs). A VMM runs on the operating system and provides facilities to execute one or more VMs, each of which is provided with a suitable complement of virtual hardware.

These VMs run independently of the host, but may interact with it as any other machine would (e.g. via network communications or other means).

VMs are allocated hardware resources by the VMM during creation, including:

Although VMs execute independently of each other and the host, they do consume host resources and, as such, the number of VMs (and their configurations) should be taken into consideration when planning host capacity.

The vmm driver requires suitable host CPU capabilities in order to provide VM services. The vmm driver requires at least one CPU with hardware-assisted virtualization capabilities and nested or extended paging capabilities to be present on the host. For more information, consult the CPU vendor's documentation.

The following ioctl(2) commands are provided for managing vmm guests:

struct vm_create_params *
Create a VM, initializing vmm if not yet started. (Does not start the VCPU.)
struct vm_run_params *
Run a VCPU for a defined VM. Return on VM-exit, when the VCPU stopped, or an error occurred.
struct vm_info_params *
Get information about the VMs currently hosted by vmm.
struct vm_terminate_params *
Terminate a given VM.
struct vm_resetcpu_params *
Reset a VCPU to power-on-init state using the provided register state.
struct vm_intr_params *
Signal a pending interrupt for a VCPU.
struct vm_rwregs_params *
Read registers of a VCPU.
struct vm_rwregs_params *
Write register values of a VCPU.
struct vm_rwvmparams_params *
Read paravirtualized hardware parameters (such as pvclock(4) version) for a VM.
struct vm_rwvmparams_params *
Write paravirtualized hardware parameters (such as pvclock(4) guest physical address) for a VM.
struct vm_mprotect_ept_params *
Set access protections on guest page table entries (only supported on hosts providing EPT or RVI).

cpu(4), intro(4), virtio(4), vmctl(8), vmd(8)

The vmm driver appeared in OpenBSD 5.9.

Mike Larkin <>

September 11, 2022 OpenBSD-current