install-scripts/cloud-init/41-qemu-hot-add-cpu.rules

# On QEMU/KVM machines we want to add memory and cpus as soon as they appear
# As of 2021-09-29, the file 40-vm-hotadd.rules does exactly the same thing for Xen and Hyper-V
ATTR{[dmi/id]sys_vendor}=="QEMU", GOTO="vm_hotadd_apply"
GOTO="vm_hotadd_end"

LABEL="vm_hotadd_apply"

# Memory hotadd request
SUBSYSTEM=="memory", ACTION=="add", DEVPATH=="/devices/system/memory/memory[0-9]*", TEST=="state", ATTR{state}!="online", ATTR{state}="online"

# CPU hotadd request
SUBSYSTEM=="cpu", ACTION=="add", DEVPATH=="/devices/system/cpu/cpu[0-9]*", TEST=="online", ATTR{online}!="1", ATTR{online}="1"

LABEL="vm_hotadd_end"