[PPT] - Introduction to Virtual Machines Introduction Abstraction and PowerPoint Presentation

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Introduction to Virtual Machines

Introduction
Abstraction and interfaces
Virtualization
Computer system architecture
Process virtual machines
System virtual machines

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Abstraction

Mechanism to manage complexity in computer

systems.

Mechanism consists of

– partition the design of a system into levels – allow higher levels to ignore the implementation details of lower levels

In computer systems, lower levels are

implemented in hardware, and higher levels in software.

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Interfaces

An interface defines the communication

boundary between two entities

– hierarchical relationship – linear relationship

Software can run on any machine supporting a

compatible interface

PowerPC MacOS MacIntosh apps. x86 Linux Linux apps x86 Windows Windows apps.

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Interfaces – Advantages

Allows de-coupling of computer design tasks

– each component provides an abstraction of itself to the

utside world
Work on different components can progress

independently

Helps manage system complexity

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Interface – Disadvantages

Software compiled for one ISA will not run on

hardware with a different ISA

– powerPC binaries on an x86 machine ?

Even if ISA's are same Oses may differ

– MS–Windows applications Sun Solaris ?

MacOS MacIntosh apps x86 x86 Windows apps. Linux

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Interface – Disadvantages (2)

Binaries may not be optimized for the platform

they run on

– Intel Pentium binaries on AMD Athlon ?

Innovation may be inhibited by a fixed ISA

– hard to change instruction sets

Application software cannot directly exploit

microprocessor implementation features

– software supposed to be implementation-neutral !

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Virtualization

Removes some constraints imposed by system

interfaces, and increases flexibility

– improves availability of application software – removes the assumption of a single management regime, improving security and failure isolation

Provide a different view to a particular computer

resource

– not necessarily a simpler view

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Virtualization (2)

Virtualization constructs an isomorphism that

maps a virtual guest system to a real host.

Si S Si ' S

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Guest Host

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V( S

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Virtualization (3)

Virtualization Vs. abstraction

– virtualization does not necessarily hide details

file file virtualization

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Virtual Machines

Concept of virtualization applied to the entire

machine.

A virtual machine is implemented by adding a

layer of software to a real machine to support the desired virtual machine’s architecture.

Virtualization

– mapping of virtual resources or state to real resources – use of real machine instructions to carry out actions specified by the virtual machine instructions

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Some Benefits of VMs

Flexibility
Portability
Isolation
Security

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Computer System Architecture

Architecture – functionality and appearance of a

computer system, but not the details of its implementation

Implementation – the actual embodiment of an

architecture

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Computer Architecture (2)

Computer systems are

built of levels of abstraction

– hierarchical abstraction – well-defined interfaces

I/O devices and Networking Controllers System Interconnect (bus) Controllers Memory Translation Execution Hardware Drivers Memory Manager Scheduler Operating System Libraries Application Programs Main Memory

Software Hardware

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The ISA Interface

Interface between

hardware and software

Important for

– OS developer

I/O devices and Networking System Interconnect (bus) Memory Translation Execution Hardware Application Programs Main Memory Operating System Libraries

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The ABI Interface

Application Binary

Interface (ABI)

– user ISA + system calls

Important for

– compiler writers

I/O devices and Networking System Interconnect (bus) Memory Translation Execution Hardware Application Programs Main Memory Operating System Libraries

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The API Interface

Application

Programming Interface (API)

– user ISA + library calls

Important for

– application programmers

I/O devices and Networking System Interconnect (bus) Memory Translation Execution Hardware Application Programs Main Memory Operating System Libraries

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Major Program Interfaces

ISA – supports all conventional software
ABI – supports application software only

System Calls User ISA System ISA

ISA

Application Software Operating System System Calls User ISA System ISA

ABI

Application Software Operating System

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Process Virtual Machines

Process virtual machine is capable of

supporting an individual process

– different guest and host ISA – couple at ABI level via runtime system

Virtualizing Software Application Process Machine OS Hardware

Guest Runtime Host

Application Process

Virtual Machine

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Process Virtual Machines (2)

Constructed at ABI level
Runtime manages guest process
Runtime communicates with

host OS

Guest processes may

intermingle with host processes

As a practical matter, binaries

built for same OS

Dynamic optimizers are a

special case

Examples: IA-32 EL, FX!32,

Dynamo

HOST OS

Disk

file sharing network communication guest process create host process guest process

runtime runtime

guest process

runtime

host process

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System Virtual Machines

System Virtual Machine capable of supporting

an OS with potentially many user processes

– couple at ISA level – eg., IBM VM/360, VMWare, Transmeta Crusoe

Hardware "Machine" OS Applications Virtualizing Software

Virtual Machine

OS Applications

Guest VMM Host

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PVM – Multiprogramming

PVM provided by a multi-process OS for each

concurrently executing application.

Combination of the OS system call interface,

and the user-level ISA.

Each process is given the illusion of having the

complete machine to itself.

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PVM – Emulators

Execute binaries compiled to a different

instruction set than that executed by the host’s hardware.

Interpretation

– low startup overhead – high steady-state per instruction emulation overhead

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PVM – Dynamic Translators

Run-time translation of blocks of source

instructions to equivalent target instructions.

– high start-up translation overhead – fast steady-state execution

Uses a code cache to

store translated blocks

f code for reuse.
e.g., Digital’s FX!32

system, Aries system, Intel IA-32 EL system

HP PA UNIX HP Apps

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PVM – Same ISA Binary Optimizers

Same source and target ISAs.
Main task is the optimization of the source

binary

– ABI level optimization – may also collect performance profiles – may also enhance security

e.g., Dynamo system, developed at Hewlett-

Packard.

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PVM – High Level Language VM

A HLL is designed for VM execution

– minimize hardware-specific and OS-specific features that could compromise portability

HLL Program Intermediate Code Memory Image Object Code (ISA) Compiler front-end Compiler back-end Loader HLL Program Portable Code (Virtual ISA ) Host Instructions

Virt. Mem. Image

Compiler VM loader VM Interpreter/Translator Traditional HLL VM

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PVM – High Level Language VM

Binary class files are distributed

– ISA part of class file (no real implementation)

OS interaction via API
e.g., Java, Microsoft CLI

Sparc Workstation Java Binary Classes x86 PC Apple Mac VM implementation VM implementation VM implementation

Java VM Architecture

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Linux process

Classic System Virtual Machine

Original meaning of the term virtual machine

– all guest and host software use the same ISA – VMM runs on bare hardware (most privileged mode) – VMM intercepts and implements all the privileged

perations for the guest OS.

Win process HOST PLATFORM

virtual network communication

Guest OS (Windows) Win process Win process Guest OS2 (Linux)

VMM

Linux process Linux process

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Hosted System Virtual Machine

Virtualizing software is built on top of an

existing host OS.

Advantages

– installation is like installing application programs – host OS provides device driver support

Drawbacks

– less efficient

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Whole System VMs

Different ISA for guest and host systems.

– both application and OS code require emulation

Implemented by placing the VMM and the

guest software on top of a conventional host OS running on the hardware

e.g., Virtual PC

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Codesigned Virtual Machines

VMs designed to enable innovative ISAs and/or

hardware implementations for improved performance, power efficiency, etc.

Similar hardware virtualization is common for

microprocessors, such as Pentium IV.

Software VM is part of the hardware design

– applications/OS never directly execute native ISA instructions

e.g., Transmeta Crusoe processor

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VM Taxonomy

Multiprogrammed Systems HLL VM

Java VM MS CLI

Codesigned VM

Transmeta Crusoe

same ISA different ISA

Process VMs System VMs

Whole System VM

Virtual PC for Mac

different ISA same ISA Classic System VM

IBM VM/370

Hosted VM

VMware

Dynamic Binary Optimizers

Dynamo

Dynamic Translators

IA-32EL, FX!32