StratoVirt Design

Overview

StratoVirt is an open-source lightweight virtualization technology based on Linux Kernel-based Virtual Machine(KVM), which reduces memory resource consumption and improves VM startup speed while retains isolation capability and security capability of traditional virtualization. StratoVirt can be applied to microservices or serverless scenarios such as function computing, and reserves interface and design for importing more features, even standard virtualization.

Architecture

The following figure shows StratoVirt's core architecture which consist of three layers from top to bottom.

• External API: StratoVirt uses the QMP protocol to communicate with external systems and is compatible with OCI. Meanwhile, StratoVirt can be managed by libvirt too.
• BootLoader: abandon the traditional BIOS+GRUB boot mode to achieve fast boot in lightweight scenarios, and provide UEFI boot support for standard VM.
• Emulated mainboard:
  • microvm: To improve performance as well as reduce the attack surface, StratoVirt minimizes the simulation of user-mode devices. KVM simulation devices and paravirtualization devices, such as GIC, serial, RTC and virtio-mmio devices are implemented;
  • standard VM: realize UEFI boot with constructed ACPI tables. Virtio-pci and VFIO devices can be attached to greatly improve the I/O performance;

Features

• High isolation ability based on hardware;
• Fast cold boot: Benefit from the minimalist design, microvm can be started within 50ms;
• Low memory overhead: StratoVirt works with a memory footprint at 4MB;
• IO enhancement: StratoVirt offers normal IO ability with minimalist IO device emulation;
• OCI compatibility: StratoVirt works with isula and kata container, and can be integrated in Kubernetes ecosystem perfectly;
• Multi-platform support: Fully support for Intel and Arm platform;
• Expansibility: StratoVirt reserves interface and design for importing more features, even expand to standard virtualization support;
• Security: less than 55 syscalls while running;

Implementation

Running Architecture

• StratoVirt VM is an independent process in Linux. The process has three types of threads: main thread, VCPU thread and I/O thread:
  • The main thread is a cycle for asynchronous collecting and processing events from external modules, such as a VCPU thread;
  • Each VCPU has a thread to process trap events of this VCPU;
  • Iothreads can be configured for I/O devices to improve I/O performance;

Restrictions

• Only the Linux operating system is supported; The recommended kernel version is 4.19;
• Only Linux is supported as the client operating system, and the recommended kernel version is 4.19;
• StratoVirt is fully tested on openEuler;
• Supports a maximum of 254 CPUs;