lectures

CS 8803CS 8803

Nate Clark

(many slides from Jim Smith)

GradesGrades

20% - Presentation 8% - Paper writeup 2% - Project proposal 8% - Status report 32% - Final project 30% - Exam

Curve

2

VMs (c) 2006, J. E. Smith 3

IntroductionIntroduction

Why virtual machines?

They allow transcending of standardized interfaces (which sometimes are an obstacle to innovation)

They enable innovation in flexible, adaptive software & hardware, security, network computing (and others)

They involve computer architecture in a pure sense

Virtualization technologies will be a key part of most future computer systems


AbstractionAbstraction

Computer systems are built on levels of abstraction

Higher level of abstraction hide details at lower levels

Example: files are an abstraction of a disk

filefile

abstraction

I/O devicesand

Networking

Controllers

System Interconnect(bus)

Controllers

MemoryTranslation

Execution Hardware

DriversMemoryManager

Scheduler

Operating System

Libraries

ApplicationPrograms

MainMemory

Software

Hardware


VirtualizationVirtualization

Similar to abstractionExcept• Same level of detail

Construct Virtual Disks• As files on a larger disk• Map state• Map operations

VMs: do the same thing with the whole “machine”

Key concepts: Map state; Map Operations

file file

virtualization


There are lots of “virtual machines”IBM VM/370JavaVMware products

The Family of Virtual MachinesThe Family of Virtual Machines

“The subjects of virtual machines and emulators have been treated as entirely separate. … they have much in common. Not only do the usual implementations have many shared characteristics, but this commonality extends to the theoretical concepts on which they are based”

-- Efrem G. Wallach, 1973

Including things not called “virtual machines” IA-32 EL

HP Dynamo Transmeta Crusoe


““Machines”Machines”

Different perspectives on what the Machine is:

OS developer Compiler developer Application programmer

Instruction Set Architecture• ISA• Major division between hardware

and software

Application Binary Interface• ABI• User ISA + OS calls

Application Program Interface• API• User ISA + library calls I/O devices

andNetworking

System Interconnect(bus)

MemoryTranslation

Execution Hardware

ApplicationPrograms

MainMemory

Operating System

Libraries


System Virtual MachinesSystem Virtual Machines

ISA level Provide a system

environment VMM manages

guest OS + apps Persistent Examples: IBM

VM/360, VMware, Transmeta Crusoe

guestprocess

HOST PLATFORM

virtualnetwork communication

Guest OS

VMM

guestprocess

guestprocess

guestprocess

Guest OS2

VMM

guestprocess

guestprocess


Process Virtual MachinesProcess Virtual Machines

ABI level Runtime manages guest

process Guest processes may

intermingle with host processes

Not persistent Guest and host OSes are

often the same Dynamic optimizers are

a special case Examples: IA-32 EL, FX!

32, Dynamo

HOST OS

Disk

file sharing

network communication

guestprocess

create

hostprocess

guestprocess

runtimeruntime

guestprocess

runtime

hostprocess

VMs (c) 2006, J. E. Smith 10

High Level Language Virtual MachinesHigh Level Language Virtual Machines

Constructed at API level• User higher level virtual ISA• OS abstracted as standard libraries

A form of process VM

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

VMs (c) 2006, J. E. Smith 11

Virtual Machine ArchitecturesVirtual Machine Architectures

Multiprogrammed

Systems

HLL VMsCo-Designed

VMs

same ISAdifferent

ISA

Process VMs System VMs

WholeSystem VMs

differentISA

same ISA

ClassicOS VMs

DynamicBinary

Optimizers

DynamicTranslators

HostedVMs

VMs (c) 2006, J. E. Smith 12

VM Technology – State MappingVM Technology – State Mapping

VM SW re-maps virtual state to real state

• Recall virtual disk• Registers to registers• Registers to memory• Memory to memory• Memory to disk

Guest Code

Guest Data

RuntimeData

RuntimeCode

Guest Registers

Host Registers

Host ABIAddress Space

HostRegister Space

VMs (c) 2006, J. E. Smith 13

VM Technology – Operation MappingVM Technology – Operation Mapping

VM SW re-maps operations on state Instruction-level state changes

• Emulation

Protected state changes• OS operations• Done under VMM control

Key concepts: Emulation and Control

VMs (c) 2006, J. E. Smith 14

VM Technology – EmulationVM Technology – Emulation

Interpretation• Software loop

decodes and dispatches each instruction

source code

dispatchloop

interpreter

routines

"data"accesses

VMs (c) 2006, J. E. Smith 15


Binary translation and code caching

• Translate blocks of instructions at a time

• Hold translated blocks in code cache

• This was a key enabler for VMware success

source code

binarytranslator

binary translatedtarget code

VMs (c) 2006, J. E. Smith 16


Staged Emulation• Emulation techniques invoked in staged manner• Based on performance tradeoffs

Code Cache

Translator/Optimizer

Binary MemoryImage

Profile Data

Interpreter Emulationmanager

VMs (c) 2006, J. E. Smith 17

Code CachesCode Caches

Contain• Basic blocks• Superblocks (one entrance, multiple exits)• Optimized Superblocks

Used in many VMs• Dynamic binary translators: Intel IA-32 EL, Compaq FX!32• Dynamic binary optimizers: Dynamo family• Co-designed virtual machines: Transmeta, IBM DAISY• High performance Java virtual machines• System VMs with “inefficiently virtualizable” ISAs• “Sandboxing” secure VMs (x86 DynamoRIO)

VMs (c) 2006, J. E. Smith 18

Code Caching with ChainingCode Caching with Chaining

Chaining of blocks in code cache minimizes VM overhead

Superblock

Dispatch table

lookup code

Superblock

Superblock

Superblock

Code Cache

VMs (c) 2006, J. E. Smith 19

VM Technology – ControlVM Technology – Control

Interpretation • Fine grain control• Every dynamic instruction “inspected” before execution

Binary translation and code caching• Coarser grain control• Every static instruction inspected before execution• Jumps to VM SW can be inserted anywhere

Protection levels• Very coarse grain control• Every resource-related instruction trapped by protection system

Otherwise, use interpretation/translation techniques• Used in system VMs

VMs (c) 2006, J. E. Smith 20

Resource Control in System VMsResource Control in System VMs

Traps and interrupts (& sys calls)• Transfer to VMM• VMM determines appropriate Guest OS• VMM transfers to Guest OS

Guest OS “return” to user app.• Transfer to VMM• VMM bounces return back to Guest app.

Resource sensitive instructions• Trap to VMM• VMM checks correctness• VMM reads/modifies guest resource• Returns to Guest

privileged operation

next instruction

check privileges

perform operation

return

system call/trap

vector location:

virtual vector location:

Application

Guest OS

VMM

system return

VMs (c) 2006, J. E. Smith 21

VMs and Computer ArchitectureVMs and Computer Architecture

Use virtualization to give computer architects a layer of software

• Beneath all conventional software• Maintains vision of hardware as seen by conventional software

Performance optimizations via Co-designed VMs• VM SW can alter/enhance architecture via emulation

Resource management – Private Virtual Machines• VM SW can manage microarchitecture resources

VMs (c) 2006, J. E. Smith 22

Co-Designed Virtual MachinesCo-Designed Virtual Machines

Separate the hardware/software interface from the ISA level of abstraction Restore the ISA to its “natural” place

as an Implementation ISA that reflects actual hardware Support existing ISAs

as a Virtual ISA Let processor designers use both hardware and software A form of system VM

OS

libs.

User Applications

V-ISA

I-ISA

Hardware

Software

Hardware

OS

libs.

User Applications

ISA

VMs (c) 2006, J. E. Smith 23

VM Technology -- Concealed MemoryVM Technology -- Concealed Memory

VM software resides in memory concealed from all conventional software

This software is available to hardware designer

Source ISA Data

CodeCache

VM Code

ICacheHierarchy

DCacheHierarchy

ProcessorCore

Source ISA Code

VM Data

concealed memory

conventionalmemory

VMs (c) 2006, J. E. Smith 24

Co-Designed VMsCo-Designed VMs

Of interest to both architects and micro-architects

• Offers opportunities for performance, power saving, fault tolerance and other implementation-dependent features

• Allows transcending conventional ISAs• Don’t confuse them with VLIW!

Early examples: IBM Daisy and Transmeta Crusoe

“pioneers are the ones with arrows in their backs”

VMs (c) 2006, J. E. Smith 25

Another Way of Doing ThingsAnother Way of Doing Things

conventional

dynamic translation

Code CacheProcessor

Pipeline

Software

Translator

Main Memory

Func.Unit

Func.Unit

. ..

Main MemoryCache

HierarchyProcessor

Pipeline

TranslationUnit

(form uops)

Func.Unit

Func.Unit

Func.Unit

. ..

TranslationUnit

(form uops)

CacheHierarchy

lectures

Technology

vm technology

designed virtual

virtual machines

binary translation

vm sw

guest os

conventional

virtual isa