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| | = 005 Virtual Machine Monitor
:page-parent: Architecture Decision Records
:page-grand_parent: About Spectrum
// SPDX-FileCopyrightText: 2022 Unikie
// SPDX-License-Identifier: GFDL-1.3-no-invariants-or-later OR CC-BY-SA-4.0
== Status
Accepted
== Context
The https://github.com/rust-vmm[rust-vmm] project provides shared components for
building Virtual Machine Monitors (VMMs) in the Rust programming language.
Rust's focus on memory safety makes it a very compelling choice for
Spectrum's VMM.
The extant rust-vmm-based VMMs are https://google.github.io/crosvm/[crosvm]
https://firecracker-microvm.github.io/[Firecracker], and
https://www.cloudhypervisor.org/[Cloud Hypervisor].
Firecracker does not support other virtio-devices than net or block.
In comparision to crosvm, Cloud Hypervisor has a more flexible IPC mechanisms,
better hotplugging support, and a more engaging community as a Linux Foundation
project. Cloud Hypervisor additionally has more core features - such as
snapshotting, live migration. crosvm supports more devices we will also need.
It will be easier to port devices from crosvm to cloud-hypervisor than to port
core features from cloud-hypervisor to crosvm.
== Decision
Spectrum will use cloud-hypervisor as the primary VMM.
== Consequences
- Some devices need to be ported from crosvm to cloud-hypervisor.
- Spectrum functionality is expected to break and not supported if the
primary VMM is swapped out.
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