OS Virtualization Tanenbaum 8 3 See references Outline

OS Virtualization Tanenbaum 8. 3 See references

Outline • • • Background What is Virtualization? Why would we want it? Why is it hard? How do we do it? Choices cs 431 -cotter 2

Micro. Kernel

What is Virtualization? • OS virtualization – Create a platform that emulates a hardware platform and allow multiple instances of an OS to use that platform, as though they have full and exclusive access to the underlying hardware cs 431 -cotter 4

What is Virtualization? Applications OS 1 OS 2 OS 3 Applications OS 4 Virtualization Platform Hardware cs 431 -cotter 5

Virtualization – Why? • Server Consolidation – Often many servers support 1 major application – Strong isolation between VMs – Virtualization saves on hardware & energy • Disaster Recovery • High Availability • Testing and Deployment cs 431 -cotter 6

Virtualization – Why? • Desktop Consolidation – Support for legacy applications – Software Development – Training cs 431 -cotter 7

The Problem • OS uses kernel mode / user mode to protect the OS. – System calls (privileged instructions) generate a trap (software interrupt) that forces a switch to kernel mode – These calls trigger sensitive instructions (I/O, MMU control, etc. ) that must only be executed by the kernel cs 431 -cotter 8

The Problem • If our VM now runs in user space, we cannot run sensitive instructions in it, since those must trap to kernel space. • Solved in 2005 with new CPUs – Intel Core 2 – VT (Virtualization Technology) – AMD Pacific – SVM (Secure Virtual Machine) – Provides new instructions that allow VM to capture traps cs 431 -cotter 9

Implementation • Type 1 Hypervisor • Type 2 Hypervisor • Paravirtualization cs 431 -cotter 10

Type 1 Hypervisor • Runs on “bare metal” • Virtual machines run in user mode – VM runs the guest OS (which thinks it is running in kernel mode) – Virtual kernel Mode – If guest OS calls sensitive instructions, hypervisor will trap and execute the instructions. – If application on guest OS calls sensitive instructions (system calls), hypervisor traps to guest OS. cs 431 -cotter 11

Type 1 Hypervisors Figure 8 -26. When the operating system in a virtual machine executes a kernel-only instruction, it traps to the hypervisor if virtualization technology is present. cs 431 -cotter Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0 -13 - 6006639 12

Type 2 Hypervisor • Runs from within a OS. • Supports guest OSs above it. – Boot from CD to load new OS – Read in code, looking for basic blocks – Then inspect basic block to find sensitive instructions. If found, replace with VM call (process called binary translation) – Then, cache block and execute. – Eventually all basic blocks will be modified and cached, and will run at near native speed. cs 431 -cotter 13

Type 2 Hypervisor Applications OS 1 OS 2 OS 3 Virtualization Platform Applications Base Operating System Hardware cs 431 -cotter 14

Paravirtualization • Modify Guest OS so that all calls to sensitive instructions are changed to hypervisor calls. • Much easier (and more efficient) to modify source code than to emulate hardware instructions (as in binary translation). • In effect, turns the hypervisor into a microkernel. cs 431 -cotter 15

Paravirtualization (1) Figure 8 -27. A hypervisor supporting both true virtualization and paravirtualization. cs 431 -cotter Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0 -13 - 6006639 16

Problems with Paravirtualization • Paravirtualized systems won’t run on native hardware • There are many different paravirtualization systems that use different commands, etc. – VMware, Xen, etc. • Proposed solution: – Modify the OS kernel so that it calls a special set of procedures to execute sensitive instructions (Virtual Machine Interface ) • Bare metal – link to library that implement code • On VM – link to VM specific library cs 431 -cotter 17

Paravirtualization (2) Figure 8 -28. VMI Linux running on (a) the bare hardware (b) VMware (c) Xen. cs 431 -cotter Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0 -13 - 6006639 18

Products (partial List) • • Microsoft – Virtual PC, Hyper-V QEMU – Processor Emulation & VM Sun Microsystems – x. VM, Virtual. Box VMware – ESX Server, Workstation, Fusion, Player, Server • Xen – Xen • Virtual. Iron cs 431 -cotter 19

Memory Virtualization • OS tracks mapping of virtual memory pages to physical memory pages. • Builds page tables, then update paging register (trap). • Allow hypervisor to manage page mapping, and use shadow page tables for the VMs cs 431 -cotter 20

Memory Virtualization • Changes to page tables do NOT trap! – One solution: Mark shadow page tables as read only. Then when VM tries to write to table, page fault traps to hypervisor. – Paravirtualized OS: Since OS has been modified to account for hypervisor, page table updates can be followed by call to hypervisor about changes. cs 431 -cotter 21

I/O Virtualization • Each guest OS holds its own “partition”. – Typically implemented as a file or region on disk – Hypervisor must convert guest OS address (block #) into physical address in region – May convert between storage types. – Must deal with DMA requests cs 431 -cotter 22

VM on Multi-core CPUs • Each core can be configured for multiple virtual machines. – A Quad-core CPU could be configured as a 32 node multi-computer – Limiting factor is often memory. Each guest OS has its own requirements (512 MB? ) cs 431 -cotter 23

Installing a Virtual machine • Will first install Virtual. Box as hypervisor • Base OS is Windows 7 • Guest OS will be Ubuntu 12. 04. 1 cs 431 -cotter 24

Installing Virtual. Box cs 431 -cotter 25

Installing Virtual. Box cs 431 -cotter 26

Installing Virtual. Box cs 431 -cotter 27

Installing Virtual. Box cs 431 -cotter 28

Installing Ubuntu VM cs 431 -cotter 29

Installing Ubuntu VM cs 431 -cotter 30

Installing Ubuntu VM cs 431 -cotter 31

Installing Ubuntu VM cs 431 -cotter 32

Installing Ubuntu VM cs 431 -cotter 33

Installing Ubuntu VM cs 431 -cotter 34

Installing Ubuntu VM cs 431 -cotter 35

Installing Ubuntu VM cs 431 -cotter 36

Summary • Virtualization provides a way to consolidate OS installations onto fewer hardware platforms • 3 basic approaches – type 1 hypervisor – type 2 hypervisor – Paravirtualization • Must also account for virtual access to shared resources (memory, I/O) cs 431 -cotter 37

References • Virtual Machine Interface – http: //vmi. ncsa. uiuc. edu/ • Virtual. Box – https: //www. virtualbox. org • Xen Hypervisor (Red Hat Linux) – http: //www. xen. org/ • Virtual PC 2007 – http: //www. microsoft. com cs 431 -cotter 38

Questions • In terms of resource allocation does a type 1 hypervisor leave more or less space for guest OSs than a type 2 hypervisor? Why? • In terms of a access to a guest OS, what is the difference between a bridged interface and a NAT interface? • What changes are needed to convert a guest OS into a paravirtualized OS? • Why has virtualization not been available on PCs until recently (2005)? cs 431 -cotter 39