virtualization - os3 · virtualization what is virtualization "a technique for hiding the...

LIA

Large Installation Administration

Virtualization

Virtualization

What is Virtualization"a technique for hiding the physical characteristics of

computing resources from the way in which other systems, applications, or end users interact with those resources."

Virtualization is the process of making things more abstract in order to make them easier to use.

Examples?

Storage virtualization

Files Linear sequence of bytes Instead of blocks on a disk (or magnetic particles)

Disk partitioning RAID - redundant array of independent disks Logical Volume management

Combines disks and partitions into logical disks.

Network virtualization

VLAN Multiple logical networks on same physical wires

Channel bonding multiple links combined offered a single, higher-

bandwidth link Computer clusters

multiple discrete computers into larger metacomputers

e.g. Hadoop Virtual NICs and bridges for VM communication

Resource virtualization

Multiprogramming Each process thinks it has CPU to itself

Virtual memory Present linear address space composed of non-

consecutive blocks of: Physical memory Disk space

Virtual MachinesVirtual Machines

Credits

Slides largely based on: “Virtual Machines: Versatile Platforms for Systems

and Processes” James E. Smith Ravi Nair

Morgan Kaufmann Publishers 2005

Why Virtual Machines?

Isolate applications in separate VMs Sandbox applications for security Support different OSes concurrently Legacy applications on legacy OSes Application testing using VMs with known state Testing OS upgrades, training OS development

Why Virtual Machines?

LIA context: Resource utilization

“Server consolidation” Facilitate maintenance Basis for cloud computing

Computer Architecture Computer Architecture RecapRecap

Instruction Set Architecture

Software

Hardware

ISA

E.g. x86_64

User + System ISA

Application Programs

Hardware

Operating System

UserISA

SystemISA

User ISA

= For doing computations Simple Memory Instructions

Move data from memory to registers and v.v. Integer Instructions Floating-Point Instructions Branch instructions

Jump to address Jump to address if ...

Part of SHA1 in assembly:

addl %esi, %e;movl %c, %esi;xorl %d, %esi;andl %b, %esi;xorl %d, %esi;

System ISA (1/2)

= Management of system resources System Resources:

Main memory Storage Other I/O devices

Management: Fair allocation between user programs Prevent concurrent/unauthorized access

Role of the Operating System

User Mode

System ISA (2/2)

OS requires special privileges over user programs OS runs in CPU Kernel mode Apps run in CPU User Mode

x86: Implemented via 2 privilege levels / rings

Kernel Mode

Ring 0 1 2 3

System ISA Instructions

Processor Management “Change to user mode + run application” Timer interrupt gives control back to OS

Memory Management Manage page table, TLB: virtual memory

I/O Management load and store to/from device

Traps “Change to kernel mode from application” On purpose (system call) or on exception

System Call Instruction

Application Programs

Hardware

Operating System

System callHandler

System call: read(file)

I/O instructions

Disk

E.g. syscall on x86 or svc on ARM.

System Call

= Mechanism for User Mode code to request services from Kernel Mode

What services? Read/write to files and devices Create processes

i.e. use Operating System abstractions: File abstraction for storing blocks on disk Process abstraction for running different code in

parallel

System Call Interface (1/2)

Application Programs

Hardware

Operating System

ISA

System calls

System Call Interface (2/2)

Read/write files or devices: open(filename, …) CreateFile(...) read(fd,data, …) ReadFile(...) write(fd,data, …) WriteFile(...) ioctl() SetConsoleMode(...)

Manipulate processes fork() CreateProcess(…) exit() ExitProcess(…)

More...

System calls via libraries

Application Programs

Hardware

Libraries

Operating System

System calls

E.g. libc

Architecture Model

Application Programs

Hardware

Libraries

Operating System

System calls

Run

Interrupts, Traps, faults

Privileged instructions

User Mode

Kernel Mode

Virtual MachinesVirtual Machines

Virtualize the machine?

What is the machine? Machine is defined by an interface 3 interfaces that can be virtualized:1. Instruction Set Architecture (ISA)2. Application Binary Interface (ABI)3. Application Programming Interface (API)

Interface 1: ISA

Application Programs

Hardware

Libraries

Operating System

System calls

ISA

Virtualize a complete machine, running an OS supporting multiple processes

= System VM

Interface 2: ABI

Application Programs

Hardware

Libraries

Operating System

ABI =System calls + user ISA

System calls

Virtualize the environment of a single process

= Process VM

Interface 3: API

Application Programs

Hardware

Libraries

Operating System

API =Libraries + user ISA

System calls

Example Virtualizing ISA

Support a machine's complete ISA VM/370 Xen* KVM*

Example Virtualizing ABI

Run binaries unmodified on different platform Sun WABI

Run Win32-x86 binaries on Solaris-SPARC Digital FX!32

Run Win32-x86 binaries on Win32-Alpha

Example Virtualizing API

Recompile applications from source Runs on any platform with same API

E.g. Linux-x86 and Linux-ARM (Assuming platform-independent code)

VM Implementations

Virtual Machine Monitor

Application Programs

Hardware

Libraries

Guest OS

Application Programs

(a) System VM (b) Process VM

Virtual Machine Monitor

Hardware

Host OS

What ISA? Same or different

Same: Run Win32-x86 on Linux-x86 Diff: Run Linux-ARM on Win32-x86

Virtual Machine Monitor

Application Programs

Hardware

Libraries

OS

Target ISA

Source ISA

Taxonomy

Same ISA

MultiprogrammedSystems

Different ISA

Emulators/Translators

High-levelLanguage VMs

Same ISA

Classic-SystemVMs

Hosted VMs

Different ISA

Whole-SystemVMs

Codesigned VMs

Process VMs System VMs

Win32native

Example: Windows Multiprogramming

Process

Win32native

Windows OS

X86 Hardware

Win32 API

One CPU, illusion of processes running in parallel

Example: Android

Java

Java VM + Libs

ARM Hardware

Linux OS

High-level Language VM (HLL-VM)

Different ISA: Java vs. ARM

Example: Android Emulation

Process

Java

Java VM

ARM VMRuntime

Linux OS Win32native

Windows OS

X86 Hardware

Win32 API

Example: Android Emulation on Xen

Java Java VM

ARM VMRuntime

Linux OSWin32Native

Windows OS

LinuxNative

LinuxNative

Linux OS

Xen Hypervisor

X86 Hardware

Xen domain

Example: VMWare

VMApp

Host OS

VMMonitor

X86 Hardware

VMDriver

Applications

Guest OS

Example: AS/400

Virtual Machine Monitor

Application Programs

Hardware

OS

Target ISA

Source ISA

Higher level ISA

Allow evolution of hardware ISA

Taxonomy Examples

Same ISA

MultiprogrammedSystems

Different ISA

Emulators/Translators

High-levelLanguage VMs

Same ISA

Classic-SystemVMs

Hosted VMs

Different ISA

Whole-SystemVMs

Codesigned VMs

Process VMs System VMs

ARM VM runtime

Java VM, MS CLR

VM/370

VMware, Xen,Docker*

UNIX

AS/400

FX!32

Implementing Virtual Machines Implementing Virtual Machines with Different ISAswith Different ISAs

VM implementation: Emulation

Emulation = implement interface of one system on another system with a different interface

Example: x86 instruction addl %edx,4(%eax)

Emulated via PowerPC instructions: lwz r4,0(r1) lddi r5,r4,4 lwzx r5,r2,r5 lwz r4,12(r1) add r5,r4,r5 stw r5,12(r1)

Emulation Model

Sa S

b

e

Source

Executing instruction e changes state of Source machine from S

a to S

b

Emulation Model

Sa

S'a

Sb

S'b

e

e'

Source

Target

Real machine has corresponding state S'a

Performs e by means of instruction(s) e'

Recall: Registers + Memory

CPU

r0

r1

r2

rN

PC MEM

Example: Change registers

e

e'

CPU MEM CPU MEM

Source

TargetCPU MEM CPU MEM

Example: Change registers

e

e'

CPU MEM CPU MEM

Source

TargetCPU MEM CPU MEM

CPU state of Source kept in Target memory, not registers!

Emulation Performance + Methods

Can be slow because of mapping Source to Target! Range of emulation methods:

Interpretation Binary translation

Interpretation: Decode a single source instruction and execute

using target instructions Binary translation:

Translate a block of source instructions once and reuse

Interpretation

Source instruction is a series of bytes Different formats

RISC: clean and simple CISC: complex with legacy Non-hardware: Java bytecodes

Complexity of format influences interpretation performance!

Example Formats

x86:

Java:

Prefixes Opcode Opcode ModR/M SIB Displace-ment Immediate

0-4 bytes optional optional optional 0,1,2,4 0,1,2,4 bytes

Opcode Index

Opcode Index1 Index2Opcode Index1

Opcode Data1 Data2Opcode

Index1

Software developer's manual: 3796 pages!

Java VM Specification: 604 pages

x86 Format

Prefixes: Repetition for strings, overrides for address and operand sizes

ModR/M: addressing mode and which register SIB: base register, index register, index scale Displacement: offset to be added to address Immediate: variable length operand

Prefixes Opcode Opcode ModR/M SIB Displace-ment Immediate

0-4 bytes optional optional optional 0,1,2,4 0,1,2,4 bytes

Binary Translation

Per-instruction interpretation slow Especially when complex

Alternative: Translate blocks of source instructions once Reuse

cf. Just-in-Time compilers Hard

Performance Tradeoff

E(n) = time needed to execute an instruction n times

Formula: E(n) = S + n*T S = startup time T = time required per emulation of the instruction

Interpretation: S low, T high

Binary translation S high, T low

Performance Tradeoff

E

n

Interpretation

Binary Translation

In practise: automatic profiling, often used code is binary translated

OS Emulation

For Process VMs have to emulate whole ABI User ISA System call interface

System call instructions (e.g. sysenter) emulated Translate from Source OS to Target OS Same OS: straightforward to hard Diff OS: straightfoward to impossible

No guarantees that Target OS has same features as Source!

E.g. fsync()