Introduction to Virtualization Technology

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Virtualization consists of multiple layers, such as hardware virtualization (which directly supports the software environment from the underlying hardware platform, also known as platform virtualization), operating system virtualization (on top of the hardware, a layer of software independent of the operational one becomes hypervisor,hypervisor to create a virtualized platform, Operating system instances run on this platform, which allows the hardware platform to be shared by multiple operating systems and applications.

Terminology of Linux Virtualization technology:

Impersonation (emulation): The process of converting one operating system (host) service into another operating system (Guest). Host and guest can be different, for example, host is x86 platform, can provide PowerPC simulation,

Two portable simulators on Linux: Qemu and Bochs are used to simulate virtualization.

Pros: You can run different guest operating systems on different host operating systems and platforms

Disadvantage: Due to the simulation of instructions, resulting in low efficiency.

Two of the most important virtualization solutions on Linux:

Citrix's Xen, which can execute both the Type1 and Type2 type of Hypervisor,amazon EC2, is using Xen for server virtualization.

Linux Kernel Virtual Machine (KVM), developed by Redhat, is integrated into the mainline kernel.

Both full virtualization and semi-virtualized require underlying hardware-assisted virtualization (Intel's VT and AMD's SVM)

KVM works by simply loading a kernel module, exporting a/DEV/KVM device, and converting the original Linux kernel into a hypervisor (the new kernel). KVM can start the new kernel's customer mode (old kernel has user mode and kernel mode). With the/DEV/KVM device, the VM makes its own address space independent of the kernel or any other VM running in the address space.

How to use: After installing KVM, you can start the guest operating system in user space, the KVM tool to operate the KVM module, and/DEV/KVM to load the guest operating system. Each guest operating system is a single process for the host operating system.

Memory is virtualized using KVM, and Io is virtualized with a slightly modified QEMU process. KVM provides a customer model for executing code that is not part of the IO portion of the operating system loaded by KVM.

The guest operating system has two modes, customer mode (non-IO operation) and user mode (IO operation, provided by QEMU. )

User guide:

The KVM kernel configuration is-->virtualization on device driver, enabling the processor to support the environment, with KVM and QEMU user space applications.

Operating system Virtualization

Virtualize the operating system itself. The operating system provides a set of user spaces that are isolated from each other and each application is limited to each user space.

Reference Links:

-IBM column of Linux virtualization technology

Introduction to Virtualization related http://xjsunjie.blog.51cto.com/999372/1322646

The world of KVM Learning Blog: http://smilejay.com/

Introduction to Virtualization Technology