VM Management

The ACRN hypervisor maintained a dedicated VM structure instance for each running VM, and a series VM APIs like create_vm, start_vm, reset_vm, shutdown_vm etc are used to switch a VM to the right state, according to the requirements of applications or system power operations.

VM structure

The acrn_vm structure is defined to manage a VM instance, this structure maintained a VM’s HW resources such as vCPU, vPIC, vIOAPIC, vUART, and vPCI. At the same time acrn_vm structure also records SW information related with corresponding VM, such as info for VM identifier, info for SW loader, info for memory e820 entries, info for IO/MMIO handlers, and info for platform level cpuid entries.

The acrn_vm structure instance will be created by create_vm API, and then work as the first parameter for other VM APIs.

VM state

Generally, a VM is not running at the beginning: it is in a ‘powered off’ state. After it is created successfully, the VM enters a ‘created’ state. Then the VM could be kicked to run, and enter a ‘started’ state. When the VM powers off, the VM returns to a ‘powered off’ state again. A VM can be paused to wait for some operation when it is running, so there is also a ‘paused’ state.

Figure 144 illustrates the state-machine of a VM state transition, please refer to CPU Virtualization for related VCPU state.

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Figure 144 Hypervisor VM State Transition

VM State Management

Pre-launched and Service VM

The hypervisor is the owner to control pre-launched and Service VM’s state by calling VM APIs directly, following the design of system power management. Please refer to ACRN power management design for more details.

Post-launched User VMs

DM takes control of post-launched User VMs’ state transition after the Service VM boots, by calling VM APIs through hypercalls.

Service VM user level service such as Life-Cycle-Service and tools such as Acrnd may work together with DM to launch or stop a User VM. Please refer to ACRN tool introduction for more details.