Problem:

Open the virtual machine manager (virt-manager), select a virtual machine, and click Open. Then, this error appears:
Error starting domain: unsupported configuration: Domain requires KVM, but it is not available. Check that virtualization is enabled in the host BIOS, and host configuration is setup to load the kvm modules.

This error appears in Ubuntu 24.04 with Kernel Linux 6.14.0-1019-oem.

Solution:

Solution 01. Load manually.

Load the kvm module; it’s different for AMD or Intel CPUs.

Step by step:

  1. Open a Terminal
    for Intel cpu: 
    sudo modprobe kvm_intel

    for AMD cpu:

    sudo modprobe kvm_amd

    Note: if you don’t know the CPU architecture of your computer, try: lscpu | grep 'Model name:'

  2. Verify it loaded: 
    lsmod | grep -E '(kvm_intel|kvm_amd)'

    The output should be a line with kvm_intel or kvm_amd.

Solution 02. Load the kvm module automatically at startup.

Step by step:

  1. Create a .conf file.
    for Intel cpu: 
     cd /etc/modprobe.d/
 sudo echo "options kvm_intel nested=1" > mykvm.conf

    for AMD cpu:

     cd /etc/modprobe.d/
 sudo echo "options kvm_amd nested=1" > mykvm.conf
  2. Restart your computer using the GUI or type in a Terminal: 
    sudo reboot
  3. (optional) If, after reboot, the error appears again try this last step: 
    sudo update-initramfs -u

    and reboot again.

NOTE⚠️: if you have installed Oracle VirtualBox, verify this!

Conflict with VirtualBox (Kernel 6.12+) If you are using a newer Ubuntu kernel (6.12+), KVM initializes immediately upon loading, locking the CPU and preventing VirtualBox from running. 

  • Solution: You can add kvm.enable_virt_at_load=0 to the kernel boot parameters.
    • If you’re using Grub on a Debian derivative (e.g. Ubuntu), edit /etc/default/grub, add the parameter kvm.enable_virt_at_load=0 to GRUB_CMDLINE_LINUX_DEFAULT, and run sudo update-grub.

NOTE⚠️: Verify the kvm module is not in a blacklist file.

If the error persists after completing all previous steps, try this.

grep -E -r "(kvm_intel|kvm_amd)" /etc/modprobe.d/

If you get output like this:

/etc/modprobe.d/blacklist-kvm.conf:blacklist kvm_intel
/etc/modprobe.d/blacklist-kvm.conf:blacklist kvm_amd

You can delete or rename this file:

sudo mv /etc/modprobe.d/blacklist-kvm.conf /etc/modprobe.d/blacklist-kvm.confBACKUP

Reboot again!

Sources:

https://www.ibm.com/docs/en/linux-on-systems?topic=kvsi-set-up-kvm-host-3
https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/virtualization_deployment_and_administration_guide/sect-nested_virt_setup
https://askubuntu.com/a/232318/822132
https://unix.stackexchange.com/a/798135/289210