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virtualization

A core idea of cloud computing is to provide centralized computing resources on the server side. These computing resources can be broken down into smaller units to serve different users independently, that is, while sharing physical resources, providing isolated, secure, trusted virtual work environments for each user, all of which inevitably rely on virtualization technology.

This virtualization of the hardware abstraction layer, also known as system virtualization, refers to virtualizing a physical computing system into one or more virtual computer hosts. Each virtual computer system (referred to as virtual machine) has its own virtual hardware, such as memory, CPU, network card and other devices, and provides an independent virtual machine execution environment. Through the emulation of a virtual machine monitor (VMM, also known as a Hypervisor), the operating system (Guest OS) in the virtual machine thinks that it is still running as an exclusive system. The operating systems in each virtual machine running on a physical machine can be completely different, and their execution environments are completely independent.

Virtualization implementation: The current mainstream virtualization can be divided into two types according to the implementation: VMM runs directly on the hardware platform, controls all hardware and manages the guest operating system. Guest operating systems run at a higher level than VMM. Xen, for example. VMM runs in a traditional operating system (Layer 1 software) and can be considered Layer 2 software, while guest operating systems are Layer 3 software. KVM and VitualBOX are such implementations. VMM can be divided into full virtualization without hardware assistance according to all virtualization platform types provided by VMM

Full virtualization based on binary translation

Hypervisor runs in Ring 0

Guest OS running on Ring 1

Mechanism: exception, catch, translation

Examples:

VMware Workstation

QEMU

Virtual PC

How it works: Hypervisor emulates a CPU to VM, guest OS does not need to make any modifications. The Hypervisor translates some of the instructions on ring0 on the guest operating system into real CPU instructions.

Paravirtualization:

Paravirtualization is also known as hypervirtualization, OS assisted virtualization

Hypervisor runs in Ring 0

Guest OS cannot run directly on Ring 0, and needs to modify the kernel. The instructions running on Ring 0 are converted to calling Hypervisor. The guest operating system runs on the virtualization platform until it runs on itself, eliminating a large number of capture simulation operations for full virtualization.

Apps on Guest OS running in Ring 3

Example: Xen

Hardware-assisted full virtualization

Intel VT and AMD-V create a new Ring-1 solely for Hypervisor use

Guest OS can use Ring 0 directly without modification

Examples:

VMware Esxi

Microsoft Hyper-V

Xen3.0

KVM

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