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.
Frequently Asked Questions (FAQ):
- See FAQ file
- Freenode, irc.freenode.net, #jailhouse
- Webchat: https://webchat.freenode.net/?channels=jailhouse
Static code analysis:
See the contribution documentation for details on how to write Jailhouse patches and propose them for upstream integration.
Hardware requirements (preliminary)
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
ARMv7 with virtualization extensions or ARMv8
At least 2 logical CPUs
Supported ARM boards:
Banana Pi (see more)
Orange Pi Zero (256 MB version)
NVIDIA Jetson TK1
ARM Versatile Express with Cortex-A15 or A7 cores (includes ARM Fast Model)
Supported ARM64 boards:
AMD Seattle / SoftIron Overdrive 3000
NVIDIA Jetson TX1
Xilinx ZCU102 (ZynqMP evaluation board)
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)
The hypervisor requires a contiguous piece of RAM for itself and each additional cell. This currently has to be pre-allocated during boot-up. On x86 this is typically done by adding
as parameter to the command line of the virtual machine's kernel. Note that if you plan to put this parameter in GRUB2 variables in /etc/default/grub, then you will need three escape characters before the dollar (e.g.
- 3.19+ for ARM
- 4.7+ for ARM64
Appropriate boot loader support (typically U-Boot)
- Linux is started in HYP mode
- PSCI support for CPU offlining
The hypervisor requires a contiguous piece of RAM for itself and each additional cell. This currently has to be pre-allocated during boot-up. On ARM this can be obtained by reducing the amount of memory seen by the kernel (through the
mem=kernel boot parameter) or by modifying the Device Tree.
Build & Installation
make, optionally specifying the target kernel directory:
It is recommended to install all of Jailhouse on your target machine. That will take care of a kernel module, the firmware, tools etc. Just call
from the top-level directory.
The traditional Linux cross-compilation (i.e.
DESTDIR=) flags are supported as well.
Running without Installation
Except for the hypervisor image
jailhouse*.bin, that has to be available in
the firmware search path, you can run Jailhouse from the build directory.
If you cannot or do not want to use
make install, you can either install just
the firmware using
make firmware_install or customize the firmware search
echo -n /path/to/jailhouse/hypervisor/ \ > /sys/module/firmware_class/parameters/path
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.
On x86 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.
On x86 the hardware capabilities can be validated by running
jailhouse hardware check sysconfig.cell
providing the binary system configuration created for the target.
Currently, there is no config generator for the ARM architecture; therefore the config file must be manually written by starting from the reference examples and checking hardware-specific datasheets, DTS and /proc entries.
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,x-buggy-eim=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 \ -netdev user,id=net -device e1000e,addr=2.0,netdev=net \ -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 \ -netdev user,id=net -device e1000e,addr=2.0,netdev=net \ -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
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 \ -s "con-base=0x2f8" -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 \ -s "con-base=0x2f8" -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.