VMs fail to start after enabling dynamic resource changes

Problem

Enabling the combination of the following parameters in the Virtual machines → select a VM → menu → Parameters → Fine-tuning settings section prevents the virtual machine from starting:

• dynamic resource changes without reboot on the Resources and limits Resources and limits tab;
  
• Host-passthrough CPU emulation mode on the Virtualization tab.
  

When attempting to start the VM, the following error occurs:

libvirt: QEMU Driver error : internal error: QEMU unexpectedly closed the monitor (vm='15_powder-hackmanite'): 2025-07-10T10:11:08.667969Z qemu-system-x86_64: -accel kvm: warning: Number of hotpluggable cpus requested (240) exceeds the recommended cpus supported by KVM (152)
Socket connected unix:/var/lib/libvirt/qemu/16-15_powder-hackmanite/monitor.sock,server=on

This error occurs on the guest OS side when using Windows. This OS has fundamental limitations in handling dynamic resource changes:

• lack of support for hot-adding CPUs or RAM at the Windows kernel level, unlike Linux systems where this functionality is implemented via ACPI and kernel modules;
• in most cases, a reboot is required to apply changes, especially when modifying processor topology or memory.

Solution

Disable dynamic resource changes:

1. Navigate to Virtual machines → select the VM → menu → Parameters → Fine-tuning settings → Resources and limits tab.
2. In the Resources section, disable the following options:
   
   • Increase CPU and RAM values without rebooting the VM;
   • Increase disk size without rebooting the VM.