Virtual Machines. Jinkyu Jeong Computer Systems Laboratory Sungkyunkwan University

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1 Virtual Machines Jinkyu Jeong Computer Systems Laboratory Sungkyunkwan University

2 Today's Topics History and benefits of virtual machines Virtual machine technologies Virtualization implementation methods Hardware-supported virtualization Cloud computing 2

Overview Fundamental idea Abstract hardware of a single computer into several different execution environments Similar to layered approach But layer creates virtual system (virtual machine, or VM) on

3 Overview Fundamental idea Abstract hardware of a single computer into several different execution environments Similar to layered approach But layer creates virtual system (virtual machine, or VM) on which operation systems or applications can run Several components Host underlying hardware system Virtual machine manager (VMM) or hypervisor creates and runs virtual machines by providing interface that is identical to the host Guest process provided with virtual copy of the host Single physical machine can run multiple operating systems concurrently, each in its own virtual machine 3

4 System Models Non-virtual machine Virtual machine 4

5 Why Virtualization? Efficient resource utilization Low resource utilization of each server machine Consolidate multiple servers on a single physical machine Flexible VM management VM suspend, resume, snapshot, clone Live migration no interruption of service Strong isolation Host system protected from VMs, VMs protected from each other Multiple OSes on a single machine Windows + Linux OS development at user-level 5

Types of VMM Type 0 hypervisors Hardware-based solutions

hypervisors Operating-system-like software built to

2 hypervisors Applications on operating systems provide

6 Types of VMM Type 0 hypervisors Hardware-based solutions IBM LPARs and Oracle LDOMs are examples Type 1 hypervisors Operating-system-like software built to provide virtualization VMware ESX, Citrix XenServer Type 2 hypervisors Applications on operating systems provide VMM features VMware Workstation, Parallels Desktop, and Oracle VirtualBox 6

7 VMM Implementation Goal Provide an illusion of multiple machines Retain control of the physical machine CPU virtualization Memory virtualization I/O virtualization 7

8 CPU Virtualization VMM runs in kernel-mode Guest OS runs in usermode Trap-and-emulate Attempting a privileged instruction in user mode causes an error -> trap VMM gains control, analyzes error, executes operation as attempted by guest Returns control to guest in user mode 8

9 x86 CPU Virtualization x86 architecture is not fully virtualizable Certain privileged instructions behave differently when run in unprivileged mode Certain unprivileged instructions can access privileged state Techniques to address inability to virtualize x86 Replace non-virtualizable instructions with easily virtualized ones statically (Para-virtualization) Perform Binary Translation (Full Virtualization) 9

10 Memory Virtualization (1) OS assumes it has full control over memory Managing physical memory and mapping virtual page to physical page VMM wants to partition physical memory among VMs VMM needs to manage physical memory VMM wants to control OS virtual page mappings OS can only map a physical page given by VMM Hardware-managed TLBs make this difficult Once TLB miss, hardware walks page tables VMM needs to control access by OS to page tables 10

11 Memory Virtualization (2) Shadow paging VMM manages a shadow of a VM s page table VM s page table is marked read-only When guest OS updates its page table Trap-and-emulate: VMM updates the shadow Page table base register sees shadow page table Para-virtualized paging Guest OS manages page table Guest OS is modified to make a call to VMM when updating its page table Hypercall VMM validates and update VM s page table Page table base register sees VM s page table 11

12 I/O Virtualization VMM provides virtual I/O devices for sharing between VMMs Full-virtualized device model Trap-and-emulate Para-virtualized device model Virtualization-aware device drivers» Front-end driver in guest OS» Back-end driver in VMM Shared memory communication specialized to virtualization Performance penalty due to virtualization overhead Devices can be shared between VMs Guest OS manages device directly No performance penalty Impossible to share a device between VMs 12

13 Hardware-supported Virtualization CPU architecture supports virtualization CPU virtualization Additional CPU modes for hypervisor e.g., VMEnter, VMExit in x86 Memory virtualization Nested paging Guest physical to machine translation by hardware I/O virtualization Virtual I/O device (function) support by harware» E.g., SR-IOV enabled network device Guest OS directly access hardware device I/O device memory access protection by IOMMU (I/O memory management unit) e.g., Intel VT-x, VT-d, AMD-V 13

14 Cloud Computing (1) On-demand self-service Ubiquitous network access Anywhere, anytime, anydevice Location-independent resource pooling Rapid elasticity Pay as you go E.g., Amazon EC2, Microsoft Azure, Google AppEngine, 14

15 Cloud Computing (2) Service models IaaS (infrastructure as a service) PaaS (Platform as a service) SaaS (Software as a service) Deployment models Private cloud Public cloud Hybrid cloud 15

Chapter 5 C. Virtual machines

Chapter 5 C. Virtual machines Chapter 5 C Virtual machines Virtual Machines Host computer emulates guest operating system and machine resources Improved isolation of multiple guests Avoids security and reliability problems Aids sharing