This document shows how to bring up ACRN as a nested hypervisor on top of QEMU/KVM with basic functionality such as running a Service VM and User VM. Running ACRN as a nested hypervisor gives you an easy way to evaluate ACRN in an emulated environment instead of setting up a separate hardware platform configuration.

This setup was tested with the following configuration:

  • ACRN hypervisor: v3.0 tag

  • ACRN kernel: acrn-v3.0 tag

  • QEMU emulator version: 4.2.1

  • Host OS: Ubuntu 20.04

  • Service VM/User VM OS: Ubuntu 20.04

  • Platforms tested: Kaby Lake, Skylake, Whiskey Lake, Tiger Lake


  1. Make sure the platform supports Intel VMX as well as VT-d technologies. On Ubuntu 20.04, this can be checked by installing the kvm-ok tool found in the cpu-checker package.

    sudo apt install cpu-checker

    Run the kvm-ok tool and if the output displays KVM acceleration can be used, the platform supports Intel VMX and VT-d technologies.

    INFO: /dev/kvm exists
    KVM acceleration can be used
  2. The host kernel version must be at least 5.3.0 or above. Ubuntu 20.04 uses a 5.8.0 kernel (or later), so no changes are needed if you are using it.

  3. Make sure KVM and the following utilities are installed.

    sudo apt update && sudo apt upgrade -y
    sudo apt install qemu-kvm virtinst libvirt-daemon-system -y

Prepare Service VM (L1 Guest)

  1. Use the virt-install command to create the Service VM.

    virt-install \
    --connect qemu:///system \
    --name ServiceVM \
    --machine q35 \
    --ram 4096 \
    --disk path=/var/lib/libvirt/images/servicevm.img,size=32 \
    --vcpus 4 \
    --virt-type kvm \
    --os-type linux \
    --os-variant ubuntu20.04 \
    --graphics none \
    --clock offset=utc,tsc_present=yes,kvmclock_present=no \
    --qemu-commandline="-machine kernel-irqchip=split -cpu Denverton,+invtsc,+lm,+nx,+smep,+smap,+mtrr,+clflushopt,+vmx,+x2apic,+popcnt,-xsave,+sse,+rdrand,-vmx-apicv-vid,+vmx-apicv-xapic,+vmx-apicv-x2apic,+vmx-flexpriority,+tsc-deadline,+pdpe1gb -device intel-iommu,intremap=on,caching-mode=on,aw-bits=48" \
    --location 'http://archive.ubuntu.com/ubuntu/dists/focal/main/installer-amd64/' \
    --extra-args "console=tty0 console=ttyS0,115200n8"
  2. Walk through the installation steps as prompted. Here are a few things to note:

    1. Make sure to install an OpenSSH server so that once the installation is complete, you can SSH into the system.

    2. We use GRUB to boot ACRN, so make sure you install it when prompted.

    3. After the installation is complete, the Service VM (guest) will restart.

  3. Log in to the Service VM guest. Find the IP address of the guest and use it to connect via SSH. The IP address can be retrieved using the virsh command as shown below.

    virsh domifaddr ServiceVM
     Name       MAC address          Protocol     Address
     vnet0      52:54:00:72:4e:71    ipv4
  4. Once logged into the Service VM, enable the serial console. Once ACRN is enabled, the virsh command will no longer show the IP.

    sudo systemctl enable serial-getty@ttyS0.service
    sudo systemctl start serial-getty@ttyS0.service
  5. Enable the GRUB menu to choose between Ubuntu and the ACRN hypervisor. Modify /etc/default/grub and edit these entries:

  6. Check the rootfs partition with lsblk, it is vda5 in this example.

  7. The Service VM guest can also be launched again later using virsh start ServiceVM --console. Make sure to use the domain name you used while creating the VM in case it is different than ServiceVM.

This concludes the initial configuration of the Service VM. The next steps will install ACRN in it.

Install ACRN Hypervisor

  1. Launch the ServiceVM Service VM guest and log into it (SSH is recommended but the console is available too).


    All the steps below are performed inside the Service VM guest that we built in the previous section.

  2. Install the ACRN build tools and dependencies following the Getting Started Guide. Note again that we’re doing these steps within the Service VM and not on a development system as described in the Getting Started Guide.

  3. Switch to the ACRN hypervisor v3.0 tag.

    cd ~
    git clone https://github.com/projectacrn/acrn-hypervisor.git
    cd acrn-hypervisor
    git checkout v3.0
  4. Build ACRN for QEMU:

    We’re using the qemu board XML and shared scenario XML files supplied from the repo (misc/config_tools/data/qemu) and not generated by the board inspector or configurator tools.

    make BOARD=qemu SCENARIO=shared

    For more details, refer to the Getting Started Guide.

  5. Install the ACRN Device Model and tools:

    sudo make install
  6. Copy acrn.32.out to the Service VM guest /boot directory.

    sudo cp build/hypervisor/acrn.32.out /boot
  7. Clone and configure the Service VM kernel repository following the instructions in the Getting Started Guide and using the acrn-v3.0 tag. The User VM (L2 guest) uses the virtio-blk driver to mount the rootfs. This driver is included in the default kernel configuration as of the acrn-v3.0 tag.

  8. Update GRUB to boot the ACRN hypervisor and load the Service VM kernel. Append the following configuration to the /etc/grub.d/40_custom.

    menuentry 'ACRN hypervisor' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-e23c76ae-b06d-4a6e-ad42-46b8eedfd7d3' {
       gfxmode $linux_gfx_mode
       insmod gzio
       insmod part_msdos
       insmod ext2
       echo 'Loading ACRN hypervisor ...'
       multiboot --quirk-modules-after-kernel /boot/acrn.32.out  root=/dev/vda5
       module /boot/vmlinuz-5.10.115-acrn-service-vm Linux_bzImage


    If your rootfs partition isn’t vda5, please change it to match with yours. vmlinuz-5.10.115-acrn-service-vm is the kernel image of Service VM.

  9. Update GRUB:

    sudo update-grub
  10. Enable networking for the User VMs:

    sudo systemctl enable systemd-networkd
    sudo systemctl start systemd-networkd
  11. Shut down the guest and relaunch it using virsh start ServiceVM --console. Select the ACRN hypervisor entry from the GRUB menu.


    You may occasionally run into the following error: Assertion failed in file arch/x86/vtd.c,line 256 : fatal error. This is a transient issue; try to restart the VM when that happens. If you need a more stable setup, you can work around the problem by switching your native host to a non-graphical environment (sudo systemctl set-default multi-user.target).

  12. Use dmesg to verify that you are now running ACRN.

    dmesg | grep ACRN
    [    0.000000] Hypervisor detected: ACRN
    [    2.337176] ACRNTrace: Initialized acrn trace module with 4 cpu
    [    2.368358] ACRN HVLog: Initialized hvlog module with 4 cpu
    [    2.727905] systemd[1]: Set hostname to <ServiceVM>.


    When shutting down the Service VM, make sure to cleanly destroy it with these commands, to prevent crashes in subsequent boots.

    virsh destroy ServiceVM # where ServiceVM is the virsh domain name.

Bring Up User VM (L2 Guest)

  1. Build the User VM disk image (UserVM.img) following Build the Ubuntu KVM Image and copy it to the Service VM (L1 guest). Alternatively you can use an Ubuntu Desktop ISO image. Rename the downloaded ISO image to UserVM.iso.

  2. Transfer the UserVM.img or UserVM.iso User VM disk image to the Service VM (L1 guest).

  3. Copy OVMF.fd to launch User VM.

    cp ~/acrn-hypervisor/devicemodel/bios/OVMF.fd ~/
  4. Update the script to use your disk image (UserVM.img or UserVM.iso).

    # Copyright (C) 2020-2022 Intel Corporation.
    # SPDX-License-Identifier: BSD-3-Clause
    function launch_ubuntu()
    logger_setting="--logger_setting console,level=5;kmsg,level=6;disk,level=5"
    #check if the vm is running or not
    vm_ps=$(pgrep -a -f acrn-dm)
    result=$(echo $vm_ps | grep "${vm_name}")
    if [[ "$result" != "" ]]; then
      echo "$vm_name is running, can't create twice!"
    #for memsize setting
    acrn-dm -m $mem_size -s 0:0,hostbridge \
    -s 3,virtio-blk,~/UserVM.img \
    -s 4,virtio-net,tap=tap0 \
    --cpu_affinity 1 \
    -s 5,virtio-console,@stdio:stdio_port \
    --ovmf ~/OVMF.fd \
    $logger_setting \
    # offline Service VM CPUs except BSP before launching User VM
    for i in `ls -d /sys/devices/system/cpu/cpu[1-99]`; do
      online=`cat $i/online`
      idx=`echo $i | tr -cd "[1-99]"`
      echo cpu$idx online=$online
      if [ "$online" = "1" ]; then
         echo 0 > $i/online
              # during boot time, cpu hotplug may be disabled by pci_device_probe during a pci module insmod
              while [ "$online" = "1" ]; do
              sleep 1
              echo 0 > $i/online
              online=`cat $i/online`
              echo $idx > /sys/devices/virtual/misc/acrn_hsm/remove_cpu
    launch_ubuntu 1