The vCPU manager is to manage all vCPU related actions, we will dive into some of the important structure members in this doc.
For now, aarch64 vCPU support is still under development, we'll introduce it when we merge runtime-rs to the master branch. (issue: #4445)
VcpuConfig is used to configure guest overall CPU info.
boot_vcpu_count is used to define the initial vCPU number.
max_vcpu_count is used to define the maximum vCPU number and it's used for the upper boundary for CPU hotplug feature
thread_per_core, cores_per_die, dies_per_socket and socket are used to define CPU topology.
vpmu_feature is used to define vPMU feature level.
If vPMU feature is Disabled, it means vPMU feature is off (by default).
If vPMU feature is LimitedlyEnabled, it means minimal vPMU counters are supported (cycles and instructions).
If vPMU feature is FullyEnabled, it means all vPMU counters are supported
There are four states for vCPU state machine: running, paused, waiting_exit, exited. There is a state machine to maintain the task flow.
When the vCPU is created, it'll turn to paused state. After vCPU resource is ready at VMM, it'll send a Resume event to the vCPU thread, and then vCPU state will change to running.
During the running state, VMM will catch vCPU exit and execute different logic according to the exit reason.
If the VMM catch some exit reasons that it cannot handle, the state will change to waiting_exit and VMM will stop the virtual machine.
When the state switches to waiting_exit, an exit event will be sent to vCPU exit_evt, event manager will detect the change in exit_evt and set VMM exit_evt_flag as 1. A thread serving for VMM event loop will check exit_evt_flag and if the flag is 1, it'll stop the VMM.
When the VMM is stopped / destroyed, the state will change to exited.
Since Dragonball Sandbox doesn't support virtualization of ACPI system, we use upcall to establish a direct communication channel between Dragonball and Guest in order to trigger vCPU hotplug.
To use upcall, kernel patches are needed, you can get the patches from upcall page, and we'll provide a ready-to-use guest kernel binary for you to try.
vCPU hot plug / hot unplug range is [1, max_vcpu_count]. Operations not in this range will be invalid.