# Alioth

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Alioth is an experimental [KVM](https://docs.kernel.org/virt/kvm/api.html)-based
type-2 hypervisor (virtual machine monitor) in Rust implemented from scratch.

> [!IMPORTANT]
>
> Disclaimer: Alioth is not an officially supported Google product.

## Quick start

- Install Alioth from source,

  ```sh
  cargo install alioth-cli --git https://github.com/google/alioth.git
  ```

- Make an initramfs with
  [u-root](https://github.com/u-root/u-root?tab=readme-ov-file#examples).

- Boot a Linux kernel with 2 CPUs and 4 GiB memory,

  ```sh
  alioth -l info --log-to-file \
      run \
      --kernel /path/to/vmlinuz \
      --cmd-line "console=ttyS0" \
      --initramfs /path/to/initramfs \
      --mem-size 4G \
      --num-cpu 2
  ```

## Features

- Runs on `x86_64` and `aarch64`.
- Boots confidential VMs with AMD SEV, SEV-ES, or SEV-SNP, see
  [coco.md](docs/coco.md) for details.
- VirtIO devices
  - `net` backed by a tap device,
  - `vsock` backed by host `/dev/vhost-vsock`,
  - `blk` backed by a raw-formatted image,
  - `entropy` backed by host `/dev/urandom`,
  - `fs` backed by [virtiofsd](https://gitlab.com/virtio-fs/virtiofsd) with
    experimental Direct Access (DAX),
  - (WIP) `balloon` with free page reporting.
- PCI device passthrough based on
  [VFIO/IOMMUFD](https://docs.kernel.org/driver-api/vfio.html#iommufd-and-vfio-iommu-type1).
- Other devices
  - serial console: 16450 on `x86_64`, pl011 on `aarch64`,
  - [fw_cfg](https://www.qemu.org/docs/master/specs/fw_cfg.html) (QEMU Firmware
    Configuration Device),
  - [pvpanic](https://www.qemu.org/docs/master/specs/pvpanic.html).

## TODOs

- [ ] explore a better solution to ACPI DSDT to replace the pre-compiled AML
      bytes,
- [ ] increase test coverage,
- [ ] add missing documents,
- [ ] (long term) port Alioth to Apple's
      [Hypervisor](https://developer.apple.com/documentation/hypervisor)
      framework,
- [ ] performance, performance, and performance!

## Acknowledgment

The virtualization implementation in Alioth takes the following projects as
references,

- [QEMU](https://gitlab.com/qemu-project/qemu.git)
- [crosvm](https://chromium.googlesource.com/crosvm/crosvm/)
- [Cloud Hypervisor](https://github.com/cloud-hypervisor/cloud-hypervisor)
- [xhyve](https://github.com/machyve/xhyve)

The [error handling](docs/error-handling.md) practice is inspired by
[GreptimeDB](https://github.com/GreptimeTeam/greptimedb)'s
[`stack_trace_debug`](https://greptimedb.rs/common_macro/attr.stack_trace_debug.html).