Processor Virtualization

This chapter introduces the concepts underlying processor virtualization and explores the many benefits to individual users and large organizations from its effective use. We will discuss the principal virtualization techniques and the open source and commercial tools that implement them.

Virtualization tools enable the emulation of instruction set-accurate representations of various computer architectures and operating systems on general-purpose computers. Virtualization is used widely in the deployment of real-world software applications in cloud environments.

After completing this chapter, you will understand the technology and benefits associated with hardware virtualization and how modern processors support virtualization at the instruction set level. You will have learned the technical features of several open source and commercial tools providing virtualization capabilities and will understand how virtualization is used to build and deploy scalable...

Technical requirements

The files for this chapter, including the answers to the exercises, are available at https://github.com/PacktPublishing/Modern-Computer-Architecture-and-Organization-Second-Edition.

Introducing virtualization

In the domain of computer architecture, virtualization refers to the use of hardware and software to create an emulated version of an environment in which a piece of software runs, as opposed to the real environment in which the code normally expects to run.

We have already looked at one form of virtualization in Chapter 7, Processor and Memory Architectures, in some depth: virtual memory. Virtual memory uses software, with supporting hardware, to create an environment in which each running application functions as if it has exclusive access to the entire computer, including all the memory it requires at the addresses it expects. This allows the virtual address ranges used by a program to be the same as those in use by other currently running processes.

Systems using virtual memory create multiple sandboxed environments in which each application runs without interference from other applications, except in competition for shared system resources.

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Virtualization challenges

In simple terms, the goal of processor virtualization is to run an operating system within a hypervisor, which itself either runs on the bare metal of a computer system or executes as an application under the control of another operating system.

In this section, we will focus on the hosted (type 2) hypervisor because this mode of operation presents a few additional challenges that a bare-metal hypervisor may not face because the type-1 hypervisor has been optimized to support virtualization.

In a type-2 hypervisor, the host operating system supports kernel and user modes, as does the guest operating system (in the guest’s perception). As the guest operating system and the applications running within it request system services, the hypervisor must intercept each request and translate it into a suitable call to the host operating system.

In a nonvirtualized system, peripheral devices such as the keyboard and mouse interact directly with...

Virtualizing modern processors

The hardware architectures of most general-purpose processor families have matured to the point where they fully support the execution of virtualized guest operating systems, at least in their higher-end variants. The following sections briefly introduce the virtualization capabilities provided by modern general-purpose processor families.

x86 processor virtualization

The x86 architecture was not originally designed to support the execution of virtualized operating systems.

As a result, x86 processors, from the earliest days through to the Pentium series, implemented instruction sets containing several unsafe but non-trapping instructions. These instructions caused problems with virtualization by, for example, allowing the guest operating system to access privileged registers that did not contain data corresponding to the state of the virtual machine.

X86 CURRENT PRIVILEGE LEVEL AND UNSAFE INSTRUCTIONS

In the x86 architecture...

Virtualization tools

In this section, we will look at several widely available open source and commercial tools that implement different forms of processor virtualization. This information may be useful as a starting point the next time you initiate a project involving virtualization.

VirtualBox

VirtualBox is a free, open source type-2 hypervisor from Oracle Corporation. Supported host operating systems include Windows and several Linux distributions. One or more guest operating systems on a single host can simultaneously run Windows, macOS, Solaris, Open Solaris, and a variety of Linux distributions.

GUEST OS LICENSING REQUIREMENTS

For organizations and individuals to remain in compliance with copyright laws, operating systems requiring licensing, such as Windows, must be properly licensed even when running as guest operating systems.

Individual virtual machines can be started, stopped, and paused under the control of the interactive VirtualBox management...

Virtualization and cloud computing

The terms virtualization and cloud computing are often tossed about with vague, sometimes overlapping meanings. Here is an attempt to highlight the difference between them:

• Virtualization is a technology for abstracting software systems from the environment in which they operate
• Cloud computing is a methodology for employing virtualization and other technologies to enable the deployment, monitoring, and control of large-scale data centers

The use of virtualization in cloud computing environments enables the flexible deployment of application workloads across an array of generic computing hardware in a controlled, coherent manner. By implementing applications such as web servers within virtual machines, it is possible to dynamically scale online computing capacity to match varying load conditions.

Commercial cloud service providers generally offer the use of their systems on a pay-per-capacity-used basis. A website that...

Summary

This chapter presented the concepts underlying processor virtualization and explained the many benefits to individual users and large organizations that derive from the effective use of virtualization. We examined the principal virtualization techniques and the open source and commercial tools that implement them.

We also saw the benefits of virtualization in the deployment of real-world software applications in cloud environments.

You should now understand the technology and benefits associated with processor virtualization and how modern processor ISAs support virtualization at the instruction set level. We learned about several open source and commercial tools providing virtualization capabilities. You should now understand how virtualization can be used to build and deploy scalable applications in cloud computing environments.

In the next chapter, we will look at the architecture of some specific application categories, including mobile devices, personal computers...

Exercises

1. Download and install the current version of VirtualBox. Download, install, and bring up Ubuntu Linux as a virtual machine within VirtualBox. Connect the guest OS to the internet using a bridged network adapter. Configure and enable clipboard sharing and file sharing between the Ubuntu guest and your host operating system.
2. Within the Ubuntu operating system you installed in Exercise 1, install VirtualBox and then install and bring up a virtual machine version of FreeDOS, available from https://www.freedos.org/download/.

   Verify that DOS commands, such as echo Hello World! and mem, perform properly in the FreeDOS virtual machine. After completing this exercise, you will have implemented an instance of nested virtualization.

3. Create two separate copies of your Ubuntu guest machine in your host system’s VirtualBox environment. Configure both Ubuntu guests to connect to the VirtualBox internal network. Set up the two machines with compatible IP...