Linux-based partitioning hypervisor
C Assembly Makefile C++ Other
Latest commit 0b85edd Aug 6, 2016 @jan-kiszka jan-kiszka arm: Fix banked guest register access
Flipping read and write had surprisingly little impact so far. But when
it had - found it while enabling HCR.TVM -, it was subtly lethal and
took a while to track down.

Signed-off-by: Jan Kiszka <>


Jailhouse is a partitioning Hypervisor based on Linux. It is able to run bare-metal applications or (adapted) operating systems besides Linux. For this purpose it configures CPU and device virtualization features of the hardware platform in a way that none of these domains, called "cells" here, can interfere with each other in an unacceptable way.

Jailhouse is optimized for simplicity rather than feature richness. Unlike full-featured Linux-based hypervisors like KVM or Xen, Jailhouse does not support overcommitment of resources like CPUs, RAM or devices. It performs no scheduling and only virtualizes those resources in software, that are essential for a platform and cannot be partitioned in hardware.

Once Jailhouse is activated, it runs bare-metal, i.e. it takes full control over the hardware and needs no external support. However, in contrast to other bare-metal hypervisors, it is loaded and configured by a normal Linux system. Its management interface is based on Linux infrastructure. So you boot Linux first, then you enable Jailhouse and finally you split off parts of the system's resources and assign them to additional cells.

WARNING: This is work in progress! Don't expect things to be complete in any dimension. Use at your own risk. And keep the reset button in reach.

Community Resources

Project home:

Source code:

Frequently Asked Questions (FAQ):

Mailing list:

Continuous integration:

Static code analysis:

See the contribution documentation for details on how to write Jailhouse patches and propose them for upstream integration.

Requirements (preliminary)

x86 architecture:

  • Intel system:

    • support for 64-bit and VMX, more precisely

      • EPT (extended page tables)
      • unrestricted guest mode
      • preemption timer
    • Intel IOMMU (VT-d) with interrupt remapping support (except when running inside QEMU)

  • or AMD system:

    • support for 64-bit and SVM (AMD-V), and also

      • NPT (nested page tables); required
      • Decode Assists; recommended
    • AMD IOMMU (AMD-Vi) is unsupported now but will be required in future

  • at least 2 logical CPUs

  • x86-64 Linux kernel (tested against >= 3.14)

    • VT-d IOMMU usage (DMAR) has to be disabled in the Linux kernel, e.g. via the command line parameter:

    • To exploit the faster x2APIC, interrupt remapping needs to be on in the kernel (check for CONFIG_IRQ_REMAP)

ARM architecture:

  • Abstract:

    • ARMv7 with virtualization extensions

    • Appropriate boot loader support (typically U-Boot)

      • Linux is started in HYP mode
      • PSCI support for CPU offlining
    • at least 2 logical CPUs

  • Board support:

    • Banana Pi (see more)

    • NVIDIA Jetson TK1

    • ARM Versatile Express with Cortex-A15 or A7 cores (includes ARM Fast Model)

On x86, hardware capabilities can be validated by running

jailhouse hardware check sysconfig.cell

using the binary system configuration created for the target (see below).

Build & Installation

Simply run make, optionally specifying the target kernel directory:

make [KDIR=/path/to/kernel/objects]

Except for the hypervisor image jailhouse*.bin that has to be available in the firmware search path (invoke make firmware_install for this), you can run Jailhouse from the build directory. Alternatively, install everything on the target machine by calling make install from the top-level directory.


Jailhouse requires one configuration file for the complete system and one for each additional cell besides the primary Linux. These .cell files have to be passed to the jailhouse command line tool for enabling the hypervisor or creating new cells.

A system configuration can be created on the target system by running the following command:

jailhouse config create sysconfig.c

In order to translate this into the required binary form, place this file in the configs/ directory. The build system will pick up every .c file from there and generate a corresponding .cell file.

Depending on the target system, the C structures may require some adjustments to make Jailhouse work properly or to reduce the desired access rights of the Linux root cell.

Configurations for additional (non-root) cells currently require manual creation. To study the structures, use one of the demo cell configurations files as reference, e.g. configs/apic-demo.c or configs/e1000-demo.c.

Demonstration in QEMU/KVM

The included system configuration qemu-vm.c can be used to run Jailhouse in QEMU/KVM virtual machine on x86 hosts (Intel and AMD are supported). Currently it requires Linux 4.4 or newer on the host side. QEMU version 2.7 or newer is required.

You also need a Linux guest image with a recent kernel (tested with >= 3.9) and the ability to build a module for this kernel. Further steps depend on the type of CPU you have on your system.

For Intel CPUs: Make sure the kvm-intel module was loaded with nested=1 to enable nested VMX support. Start the virtual machine as follows:

qemu-system-x86_64 -machine q35,kernel_irqchip=split -m 1G -enable-kvm \
    -smp 4 -device intel-iommu,intremap=on \
    -cpu kvm64,-kvm_pv_eoi,-kvm_steal_time,-kvm_asyncpf,-kvmclock,+vmx \
    -drive file=LinuxInstallation.img,format=raw|qcow2|...,id=disk,if=none \
    -device ide-hd,drive=disk -serial stdio -serial vc \
    -device intel-hda,addr=1b.0 -device hda-duplex

For AMD CPUs: Make sure the kvm-amd module was loaded with nested=1 to enable nested SVM support. Start the virtual machine as follows:

qemu-system-x86_64 -machine q35 -m 1G -enable-kvm -smp 4 \
    -cpu host,-kvm_pv_eoi,-kvm_steal_time,-kvm_asyncpf,-kvmclock \
    -drive file=LinuxInstallation.img,format=raw|qcow2|...,id=disk,if=none \
    -device ide-hd,drive=disk -serial stdio -serial vc \
    -device intel-hda,addr=1b.0 -device hda-duplex

Inside the VM, make sure that jailhouse-*.bin, generated by the build process, are available for firmware loading (typically /lib/firmware), see above for installation steps.

The hypervisor requires a contiguous piece of RAM for itself and each additional cell. This currently has to be pre-allocated during boot-up. So you need to add


as parameter to the command line of the virtual machine's kernel. The Jailhouse QEMU cell config will block use of the serial port by the guest OS, so make sure that the guest kernel command line does NOT have its console set to log to the serial port (ie remove any 'console=ttyS0' arguments from the grub config). Reboot the guest and load jailhouse.ko. Then enable Jailhouse like this:

jailhouse enable /path/to/qemu-vm.cell

Next you can create a cell with a demonstration application as follows:

jailhouse cell create /path/to/apic-demo.cell
jailhouse cell load apic-demo /path/to/apic-demo.bin -a 0xf0000
jailhouse cell start apic-demo

apic-demo.bin is left by the built process in the inmates/demos/x86 directory. This application will program the APIC timer interrupt to fire at 10 Hz, measuring the jitter against the PM timer and displaying the result on the console. Given that this demonstration runs in a virtual machine, obviously no decent latencies should be expected.

After creation, cells are addressed via the command line tool by providing their names or their runtime-assigned IDs. You can obtain information about active cells this way:

jailhouse cell list

Cell destruction is performed by specifying the configuration file of the desired cell. This command will destroy the apic-demo:

jailhouse cell destroy apic-demo

Note that the first destruction or shutdown request on the apic-demo cell will fail. The reason is that this cell contains logic to demonstrate an ordered shutdown as well as the ability of a cell to reject shutdown requests.

The apic-demo cell has another special property for demonstration purposes: As long as it is running, no cell reconfigurations can be performed - the apic-demo locks the hypervisor in this regard. In order to destroy another cell or create an additional one, shut down the apic-demo first.

jailhouse cell shutdown apic-demo  # call again if error is returned

To demonstrate the execution of a second, non-Linux cell, issue the following commands:

jailhouse cell create /path/to/pci-demo.cell
jailhouse cell load pci-demo /path/to/pci-demo.bin -a 0xf0000
jailhouse cell start pci-demo

The pci-demo will use the second serial port provided by QEMU. You will find its output in a virtual console of the QEMU window. The purpose of this demo is to show basic PCI device configuration and MSI handling.

While cell configurations are locked, it is still possible, though, to reload the content of existing cell (provided they accept their shutdown first). To reload and restart the tiny-demo, issue the following commands:

jailhouse cell start apic-demo
jailhouse cell load pci-demo /path/to/pci-demo.bin -a 0xf0000
jailhouse cell start pci-demo

Finally, Jailhouse is can be stopped completely again:

jailhouse disable  # call again on error due to running apic-demo

All non-Linux cells running at that point will be destroyed, and resources will be returned to Linux.