Cloud Hypervisor is an open source Virtual Machine Monitor (VMM) that runs on top of the KVM hypervisor and the Microsoft Hypervisor (MSHV).
The project focuses on running modern, Cloud Workloads, on specific, common, hardware architectures. In this case Cloud Workloads refers to those that are run by customers inside a Cloud Service Provider. This means modern operating systems with most I/O handled by paravirtualised devices (e.g. virtio), no requirement for legacy devices, and 64-bit CPUs.
Cloud Hypervisor is implemented in Rust and is based on the Rust VMM crates.
Cloud Hypervisor supports the x86-64, AArch64 and riscv64
architectures, with functionality varying across these platforms. The
functionality differences between x86-64 and AArch64 are documented
in #1125.
The riscv64 architecture support is experimental and offers limited
functionality. For more details and instructions, please refer to riscv
documentation.
Cloud Hypervisor supports 64-bit Linux and Windows 10/Windows Server 2019.
The following sections describe how to build and run Cloud Hypervisor.
For required KVM functionality and adequate performance the recommended host kernel version is 5.13. The majority of the CI currently tests with kernel version 5.15.
The recommended approach to getting started with Cloud Hypervisor is by using a
pre-built binary. Binaries are available for the latest
release.
Use cloud-hypervisor-static for x86-64 or cloud-hypervisor-static-aarch64
for AArch64 platform.
For convenience, packages are also available targeting some popular Linux distributions. This is thanks to the Open Build Service. The OBS README explains how to enable the repository in a supported Linux distribution and install Cloud Hypervisor and accompanying packages. Please report any packaging issues in the obs-packaging repository.
Please see the instructions for building from source if you do not wish to use the pre-built binaries.
Cloud Hypervisor boots guests in one of two ways. The first is direct
kernel boot, where a kernel image is passed to --kernel. The x86-64
kernel must be built with PVH support or be a bzImage. The second is
firmware boot, where a firmware image is passed to --firmware and
brings up the guest's normal boot loader.
Two firmware options are supported, and which one works best depends
on the guest OS. Rust Hypervisor
Firmware
is a lightweight Rust-based PVH firmware. The edk2 UEFI firmware is
called CLOUDHV.fd for x86-64 and CLOUDHV_EFI.fd for AArch64.
Prebuilt binaries for both are available at their respective releases
pages, Rust Hypervisor
Firmware
and our edk2
fork.
The edk2 fork carries customizations required to boot AArch64 guests
on cloud-hypervisor. See docs/uefi.md for differences
with upstream tianocore/edk2.
Cloud Hypervisor supports booting disk images containing all needed components to run cloud workloads, a.k.a. cloud images.
The following sample commands will download an Ubuntu Cloud image, converting it into a format that Cloud Hypervisor can use and a firmware to boot the image with.
$ wget https://cloud-images.ubuntu.com/focal/current/focal-server-cloudimg-amd64.img
$ qemu-img convert -p -f qcow2 -O raw focal-server-cloudimg-amd64.img focal-server-cloudimg-amd64.raw
$ wget https://github.com/cloud-hypervisor/rust-hypervisor-firmware/releases/download/0.4.2/hypervisor-fw
The Ubuntu cloud images do not ship with a default password so it necessary to
use a cloud-init disk image to customise the image on the first boot. A basic
cloud-init image is generated by this script.
This seeds the image with a default username/password of cloud/cloud123. It
is only necessary to add this disk image on the first boot. Script also assigns
default IP address using test_data/cloud-init/ubuntu/local/network-config details
with --net "mac=12:34:56:78:90:ab,tap=" option. Then the matching mac address
interface will be enabled as per network-config details.
$ sudo setcap cap_net_admin+ep ./cloud-hypervisor
$ ./create-cloud-init.sh
$ ./cloud-hypervisor \
--firmware ./hypervisor-fw \
--disk path=focal-server-cloudimg-amd64.raw path=/tmp/ubuntu-cloudinit.img \
--cpus boot=4 \
--memory size=1024M \
--net "tap=,mac=,ip=,mask="
If access to the firmware messages or interaction with the boot loader (e.g.
GRUB) is required then it necessary to switch to the serial console instead of
virtio-console.
$ ./cloud-hypervisor \
--kernel ./hypervisor-fw \
--disk path=focal-server-cloudimg-amd64.raw path=/tmp/ubuntu-cloudinit.img \
--cpus boot=4 \
--memory size=1024M \
--net "tap=,mac=,ip=,mask=" \
--serial tty \
--console off
--firmware vs --kernelThe following scenarios are supported by Cloud Hypervisor to bootstrap a VM, i.e., to load a payload/bootitem(s):
Please note that our Cloud Hypervisor firmware (hypervisor-fw) has a Xen PVH
boot entry, therefore it can also be booted via the --kernel parameter, as
seen in some examples.
Cloud Hypervisor also supports direct kernel boot. For x86-64, a vmlinux ELF kernel (compiled with PVH support) or a regular bzImage are supported. In order to support development there is a custom branch; however provided the required options are enabled any recent kernel will suffice.
To build the kernel:
# Clone the Cloud Hypervisor Linux branch
$ git clone --depth 1 https://github.com/cloud-hypervisor/linux.git -b ch-6.12.8 linux-cloud-hypervisor
$ pushd linux-cloud-hypervisor
$ make ch_defconfig
# Do native build of the x86-64 kernel
$ KCFLAGS="-Wa,-mx86-used-note=no" make bzImage -j `nproc`
# Do native build of the AArch64 kernel
$ make -j `nproc`
$ popd
For x86-64, the vmlinux kernel image will then be located at
linux-cloud-hypervisor/arch/x86/boot/compressed/vmlinux.bin.
For AArch64, the Image kernel image will then be located at
linux-cloud-hypervisor/arch/arm64/boot/Image.
For the disk image the same Ubuntu image as before can be used. This contains
an ext4 root filesystem.
$ wget https://cloud-images.ubuntu.com/focal/current/focal-server-cloudimg-amd64.img # x86-64
$ wget https://cloud-images.ubuntu.com/focal/current/focal-server-cloudimg-arm64.img # AArch64
$ qemu-img convert -p -f qcow2 -O raw focal-server-cloudimg-amd64.img focal-server-cloudimg-amd64.raw # x86-64
$ qemu-img convert -p -f qcow2 -O raw focal-server-cloudimg-arm64.img focal-server-cloudimg-arm64.raw # AArch64
These sample commands boot the disk image using the custom kernel whilst also supplying the desired kernel command line.
$ sudo setcap cap_net_admin+ep ./cloud-hypervisor
$ ./create-cloud-init.sh
$ ./cloud-hypervisor \
--kernel ./linux-cloud-hypervisor/arch/x86/boot/compressed/vmlinux.bin \
--disk path=focal-server-cloudimg-amd64.raw path=/tmp/ubuntu-cloudinit.img \
--cmdline "console=hvc0 root=/dev/vda1 rw" \
--cpus boot=4 \
--memory size=1024M \
--net "tap=,mac=,ip=,mask="
$ sudo setcap cap_net_admin+ep ./cloud-hypervisor
$ ./create-cloud-init.sh
$ ./cloud-hypervisor \
--kernel ./linux-cloud-hypervisor/arch/arm64/boot/Image \
--disk path=focal-server-cloudimg-arm64.raw path=/tmp/ubuntu-cloudinit.img \
--cmdline "console=hvc0 root=/dev/vda1 rw" \
--cpus boot=4 \
--memory size=1024M \
--net "tap=,mac=,ip=,mask="
If earlier kernel messages are required the serial console should be used instead of virtio-console.
$ ./cloud-hypervisor \
--kernel ./linux-cloud-hypervisor/arch/x86/boot/compressed/vmlinux.bin \
--console off \
--serial tty \
--disk path=focal-server-cloudimg-amd64.raw \
--cmdline "console=ttyS0 root=/dev/vda1 rw" \
--cpus boot=4 \
--memory size=1024M \
--net "tap=,mac=,ip=,mask="
$ ./cloud-hypervisor \
--kernel ./linux-cloud-hypervisor/arch/arm64/boot/Image \
--console off \
--serial tty \
--disk path=focal-server-cloudimg-arm64.raw \
--cmdline "console=ttyAMA0 root=/dev/vda1 rw" \
--cpus boot=4 \
--memory size=1024M \
--net "tap=,mac=,ip=,mask="
Cloud Hypervisor is under active development. The following stability guarantees are currently made:
The API (including command line options) will not be removed or changed in a breaking way without a minimum of 2 major releases notice. Where possible warnings will be given about the use of deprecated functionality and the deprecations will be documented in the release notes.
Point releases will be made between individual releases where there are substantial bug fixes or security issues that need to be fixed. These point releases will only include bug fixes.
Currently the following items are not guaranteed across updates:
Further details can be found in the release documentation.
As of 2023-01-03, the following cloud images are supported:
Direct kernel boot to userspace should work with a rootfs from most distributions although you may need to enable exotic filesystem types in the reference kernel configuration (e.g. XFS or btrfs.)
Cloud Hypervisor supports hotplug of CPUs, passthrough devices (VFIO),
virtio-{net,block,pmem,fs,vsock} and memory resizing. This
document details how to add devices to a running VM.
Details of the device model can be found in this documentation.
The project roadmap is tracked through a GitHub project.
In order to satisfy the design goal of having a high-performance, security-focused hypervisor the decision was made to use the Rust programming language. The language's strong focus on memory and thread safety makes it an ideal candidate for implementing VMMs.
Instead of implementing the VMM components from scratch, Cloud Hypervisor is importing the Rust VMM crates, and sharing code and architecture together with other VMMs like e.g. Amazon's Firecracker and Google's crosvm.
Cloud Hypervisor embraces the Rust VMM project's goals, which is to be able to share and re-use as many virtualization crates as possible.
A large part of the Cloud Hypervisor code is based on either
$ claude mcp add cloud-hypervisor \
-- python -m otcore.mcp_server <graph>