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computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, e ...
, hardware-assisted virtualization is a
platform virtualization Hardware virtualization is the virtualization of computers as complete hardware platforms, certain logical abstractions of their componentry, or only the functionality required to run various operating systems. Virtualization hides the physica ...
approach that enables efficient
full virtualization In computer science, virtualization is a modern technique developed in late 1990s and is different from simulation and emulation. Virtualization employs techniques used to create instances of an environment, as opposed to simulation, which model ...
using help from hardware capabilities, primarily from the host processors. A full virtualization is used to emulate a complete hardware environment, or
virtual machine In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardw ...
, in which an unmodified guest
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
(using the same
instruction set In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ' ...
as the host machine) effectively executes in complete isolation. Hardware-assisted virtualization was added to
x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was introd ...
processors (
Intel VT-x x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-a ...
, AMD-V or VIA VT) in 2005, 2006 and 2010 (respectively). Hardware-assisted virtualization is also known as accelerated virtualization; Xen calls it hardware virtual machine (HVM), and Virtual Iron calls it native virtualization.


History

Hardware-assisted virtualization first appeared on the
IBM System/370 The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path ...
in 1972, for use with
VM/370 VM (often: VM/CMS) is a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules (emulator), Hercules emulator for personal computers. The ...
, the first virtual machine operating system. With the increasing demand for high-definition computer graphics (e.g.
CAD Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve co ...
), virtualization of mainframes lost some attention in the late 1970s, when the upcoming
minicomputer A minicomputer, or colloquially mini, is a class of smaller general purpose computers that developed in the mid-1960s and sold at a much lower price than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, ...
s fostered resource allocation through
distributed computing A distributed system is a system whose components are located on different computer network, networked computers, which communicate and coordinate their actions by message passing, passing messages to one another from any system. Distributed com ...
, encompassing the commoditization of
microcomputer A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (PC ...
s. IBM offers
hardware virtualization Hardware virtualization is the virtualization of computers as complete hardware platforms, certain logical abstractions of their componentry, or only the functionality required to run various operating systems. Virtualization hides the physica ...
for its
IBM Power Systems Power Systems is a family of server computers from IBM that are based on its Power processors. It was created in 2008 as a merger of the System p and System i product lines. History IBM had two distinct POWER- and PowerPC-based hardware l ...
hardware for
AIX Aix or AIX may refer to: Computing * AIX, a line of IBM computer operating systems *An Alternate Index, for a Virtual Storage Access Method Key Sequenced Data Set * Athens Internet Exchange, a European Internet exchange point Places Belgi ...
,
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...
and IBM i, and for its IBM- Mainframes
System z IBM Z is a family name used by IBM for all of its z/Architecture mainframe computers. In July 2017, with another generation of products, the official family was changed to IBM Z from IBM z Systems; the IBM Z family now includes the newest mode ...
. IBM refers to its specific form of hardware virtualization as "logical partition", or more commonly as
LPAR A logical partition (LPAR) is a subset of a computer's hardware resources, virtualized as a separate computer. In effect, a physical machine can be partitioned into multiple logical partitions, each hosting a separate instance of an operating ...
. The increase in compute capacity per x86 server (and in particular the substantial increase in modern networks' bandwidths) rekindled interest in data-center based computing which is based on virtualization techniques. The primary driver was the potential for server consolidation: virtualization allowed a single server to cost-efficiently consolidate compute power on multiple underutilized dedicated servers. The most visible hallmark of a return to the roots of computing is
cloud computing Cloud computing is the on-demand availability of computer system resources, especially data storage ( cloud storage) and computing power, without direct active management by the user. Large clouds often have functions distributed over mul ...
, which is a synonym for data center based computing (or mainframe-like computing) through high bandwidth networks. It is closely connected to virtualization. The initial implementation x86 architecture did not meet the
Popek and Goldberg virtualization requirements The Popek and Goldberg virtualization requirements are a set of conditions sufficient for a computer architecture to support system virtualization efficiently. They were introduced by Gerald J. Popek and Robert P. Goldberg in their 1974 article "F ...
to achieve "classical virtualization": * equivalence: a program running under the virtual machine monitor (VMM) should exhibit a behavior essentially identical to that demonstrated when running on an equivalent machine directly * resource control (also called safety): the VMM must be in complete control of the virtualized resources * efficiency: a statistically dominant fraction of machine instructions must be executed without VMM intervention This made it difficult to implement a virtual machine monitor for this type of processor. Specific limitations included the inability to
trap A trap is a mechanical device used to capture or restrain an animal for purposes such as hunting, pest control, or ecological research. Trap or TRAP may also refer to: Art and entertainment Films and television * ''Trap'' (2015 film), Fil ...
on some privileged instructions. To compensate for these architectural limitations, designers have accomplished virtualization of the x86 architecture through two methods: full virtualization or paravirtualization. Both create the illusion of physical hardware to achieve the goal of operating system independence from the hardware but present some trade-offs in performance and complexity. # Full virtualization was implemented in first-generation x86 VMMs. It relies on
binary translation In computing, binary translation is a form of binary recompilation where sequences of instructions are translated from a ''source'' instruction set to the ''target'' instruction set. In some cases such as instruction set simulation, the target ...
to trap and virtualize the execution of certain sensitive, non-virtualizable instructions. With this approach, critical instructions are discovered (statically or dynamically at run-time) and replaced with traps into the VMM to be emulated in software. Binary translation can incur a large performance overhead in comparison to a virtual machine running on natively virtualized architectures such as the IBM System/370.
VirtualBox Oracle VM VirtualBox (formerly Sun VirtualBox, Sun xVM VirtualBox and Innotek VirtualBox) is a type-2 hypervisor for x86 virtualization developed by Oracle Corporation. VirtualBox was originally created by Innotek GmbH, which was acquired by S ...
,
VMware Workstation VMware Workstation Pro (known as VMware Workstation until release of VMware Workstation 12 in 2015) is a hosted (Type 2) hypervisor that runs on x64 versions of Windows and Linux operating systemshttps://kb.vmware.com/selfservice/microsites/sear ...
(for 32-bit guests only), and
Microsoft Virtual PC Windows Virtual PC (successor to Microsoft Virtual PC 2007, Microsoft Virtual PC 2004, and Connectix Virtual PC) is a virtualization program for Microsoft Windows. In July 2006, Microsoft released the Windows version free of charge. In August ...
, are well-known commercial implementations of full virtualization. #
Paravirtualization In computing, paravirtualization or para-virtualization is a virtualization technique that presents a software interface to the virtual machines which is similar, yet not identical, to the underlying hardware–software interface. The intent o ...
is a technique in which the hypervisor provides an API and the OS of the guest virtual machine calls that API, requiring OS modifications. In 2005 and 2006,
Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...
and
AMD Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufactur ...
(working independently) created new processor extensions to the
x86 architecture x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was int ...
called Intel VT-x and AMD-V, respectively. On the
Itanium Itanium ( ) is a discontinued family of 64-bit Intel microprocessors that implement the Intel Itanium architecture (formerly called IA-64). Launched in June 2001, Intel marketed the processors for enterprise servers and high-performance comput ...
architecture, hardware-assisted virtualization is known as VT-i. The first generation of x86 processors to support these extensions were released in late 2005 early 2006: *On November 13, 2005, Intel released two models of Pentium 4 (Model 662 and 672) as the first Intel processors to support VT-x. *On May 23, 2006, AMD released the Athlon 64 ("Orleans"), the Athlon 64 X2 ("Windsor") and the Athlon 64 FX ("Windsor") as the first AMD processors to support this technology. Well-known implementations of hardware-assisted x86 virtualization include VMware Workstation (for 64-bit guests only), XenCenter, Xen 3.x (including derivatives like Virtual Iron), Linux KVM and
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
Hyper-V Microsoft Hyper-V, codenamed Viridian, and briefly known before its release as Windows Server Virtualization, is a native hypervisor; it can create virtual machines on x86-64 systems running Windows. Starting with Windows 8, Hyper-V superseded W ...
.


Advantages

Hardware-assisted virtualization reduces the maintenance overhead of paravirtualization as it reduces (ideally, eliminates) the changes needed in the guest operating system. It is also considerably easier to obtain better performance. A practical benefit of hardware-assisted virtualization has been cited by VMware engineers and Virtual Iron.


Disadvantages

Hardware-assisted virtualization requires explicit support in the host CPU, which is available on not all x86/x86_64 processors. A "pure" hardware-assisted virtualization approach, using entirely unmodified guest operating systems, involves many VM traps, and thus high CPU overheads, limiting scalability and the efficiency of server consolidation. This performance hit can be mitigated by the use of paravirtualized drivers; the combination has been called "hybrid virtualization". In 2006 first-generation 32- and 64-bit x86 hardware support was found rarely to offer performance advantages over software virtualization.A Comparison of Software and Hardware Techniques for x86 Virtualization, Keith Adams and Ole Agesen, VMware, ASPLOS’06 October 21–25, 2006, San Jose, California, USA
Surprisingly, we find that the first-generation hardware support rarely offers performance advantages over existing software techniques. We ascribe this situation to high VMM/guest transition costs and a rigid programming model that leaves little room for software flexibility in managing either the frequency or cost of these transitions.


See also

*
Intel VT-d x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-as ...
* Further refinements of hardware-assisted virtualization are possible using an IOMMU; this allows native-speed access to dedicated hardware from a guest operating system, including DMA-capable hardware * Second Level Address Translation (SLAT), implementations including
Rapid Virtualization Indexing Second Level Address Translation (SLAT), also known as nested paging, is a hardware-assisted virtualization technology which makes it possible to avoid the overhead associated with software-managed shadow page tables. AMD has supported SLAT through ...
or Extended Page Tables * Other virtualization techniques include
operating system-level virtualization OS-level virtualization is an operating system (OS) paradigm in which the Kernel (computer science), kernel allows the existence of multiple isolated user space instances, called ''containers'' (LXC, Solaris Containers, Solaris containers, Docker ...
, as practiced by Parallels Virtuozzo Containers, and
application virtualization Application virtualization is a software technology that encapsulates computer programs from the underlying operating system on which they are executed. A fully virtualized application is not installed in the traditional sense, although it is sti ...
. *
Nanokernel In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management ...
*
Hardware emulation In integrated circuit design, hardware emulation is the process of imitating the behavior of one or more pieces of hardware (typically a system under design) with another piece of hardware, typically a special purpose emulation system. The emu ...
*
Emulator In computing, an emulator is hardware or software that enables one computer system (called the ''host'') to behave like another computer system (called the ''guest''). An emulator typically enables the host system to run software or use pe ...
* JTAG *
Background Debug Mode interface Background debug mode (BDM) interface is an electronic interface that allows debugging of embedded systems. Specifically, it provides in-circuit debugging functionality in microcontrollers. It requires a single wire and specialized electronics ...
* In-circuit emulator


References


Further reading

* * * * * * {{DEFAULTSORT:Hardware-Assisted Virtualization Hardware virtualization