Server virtualization concepts allow partitioning of physical servers into multiple virtual servers using virtualization software and hardware techniques. This improves resource utilization by running multiple virtual machines on a single physical server. Server virtualization provides benefits like reduced costs, higher efficiency, lower power consumption, and improved availability compared to running each application on its own physical server. Key components of server virtualization include virtual machines, hypervisors, CPU virtualization using techniques like Intel VT-x or AMD-V, memory virtualization, and I/O virtualization through methods like emulated, paravirtualized or direct I/O. KVM and QEMU are popular open source virtualization solutions, with KVM providing kernel-level virtualization support and Q

1. Server Virtualization Concepts
Kingston Smiler. S (kingstonsmiler@gmail.com)

2. About Me
Author
•“OpenFlow CookBook”, which is one
of the recognized study material by
ONF (Open Networking Foundation)
•Learning CoreOS
•1 RFC & 2 IETF Drafts in MPLS and
TRILL WG
•Frequent Presenter in various
networking Forums
•Trainer of SDN, NFV and Network
Virtualization Concepts
Experience
•14+ years of Industry Experience
•6+ years of experience in SDN, NFV
and OpenFlow
•Working as a pre-sales consultant
and product manager
•Having Work Experience in all the
three commercial L2, L3 networking
stack (IPInfusion ZebOS, Aricent ISS,
MetaSwitch L2,L3 and MPLS stack)

3. Levels of Server Virtualization
Types of Server Virtualization
Components of Server Virtualization
HyperVisors
Virtual Machine
Containers
Dockers

4. Server Virtualization
Wikipedia Definition
Partitioning of physical server into
number of small virtual servers
Uses Virtualization Software and
hardware virtualization techniques
In most cases the servers are not
utilized fully which results in
inefficient usage

5. Why Server Virtualization
Less Resource Utilization
High Cost
Power Consumption
Server Downtime
High Infrastructure

6. History of Server Virtualization
IBM Mainframes
with Virtualization
Evolution of
Personal
Computers
(1990s)
Back to
virtualization to
reduce Capex and
Opex
(2000s)
1970s 1990s 2000s

7. IBM Mainframes
IBM CP-67 (Mid
1960s)
First Virtualized IBM Mainframe
Server
Split the computer into multiple
virtual machines
Different “tasks” can be run separately
and independently on the same
mainframe
If one virtual machine or “task” has a
problem, other virtual machines are
unaffected

8. Personal Computer Evolution
• Introduction of Intel/AMD servers (x86 architecture)
• Each PC/server runs its own OS (Windows / Unix) and runs application.
• Best approach for personal computers.
• For server and IT infrastructure brings overhead while going for massive
scale.
• Typically in IT and infrastructure deployment one server runs one
application (Email Server, Application Server, DB Server etc)
File
Server
Web
Server
File
Server
Web
Server
File
Server
Domain
Server
App
Server
DNS
Server
Each Server Running
1 Application

9. Server Virtualization

10. Physical Server vs Virtual Server

11. Components of Server Virtualization
Virtual Machine
Software Implementation of a
machine that executes program
like a physical machine.
Host Operating System
Operating System actually
running in the server / hardware
Guest Operating System
The Operating System running
in the simulated virtual machine
HyperVisor or VMM
The Operating System running in the
simulated virtual machine
Host Operating System
Hardware -- “real machine”
Virtual
Machine
Guest Operating
System
APP APP
Virtual
Machine
Guest Operating
System
APP APP
Hypervisor / VMM

12. Virtual Machine
System Virtual Machine
Full Virtualization VMs run
directly on the server
infrastructure without any
general purpose OS
Hardware -- “real machine”
Virtual Machine Monitor (VMM)
Simulated
Machine
Operating
System
APP APP
Simulated
Machine
Operating
System
APP APP
Hardware -- “real machine”
Host Operating System
Simulated
Machine
Operating
System
APP APP
Simulated
Machine
Operating
System
APP APP
Process Virtual Machine?
Needs host operating system
Virtual Machine running as a
process in the host OS

13. HyperVisor
Hypervisor
Hypervisor is a variant of supervisor
and is the “Supervisor of Supervisor”
Piece of computer software, firmware
or hardware that creates and runs VM
Presents the guest operating system a
virtual operating platform and
manages the execution of guest OS
Multiple instances of a variety of
operating systems may share the
virtualized hardware resources

14. Type 1 Hypervisors
• Also known as bare-metal implementation
• They sit directly on the top of hardware, without needing any operating
system.
• Since they can directly communicate with hardware resources, they are
much faster than type 2 hypervisor
Pro’s
• Single virtual machine crash does not
affect rest of guest system.
• More Secure than type2.
• Generate less overhead and fast.
Example
Vmware Esx, Microsoft Hyper-V

15. Type 2 Hypervisors
• Type 2 hypervisor resides on top of the operating system.
• They cannot directly communicate with the hardware, they are less
efficient than the type 1
Pro’s
• Install is easier.
• OS takes care of all the hardware, that’s
why can support wide range of
hardware.
Con’s
• More points of failure, anything that
affects the stability of base os can also
affect the guest os.
Examples
KVM, VirtualBox

16. Server Virtualization Components
Server
Virtualization
CPU
Virtualization
Memory
Virtualization
I/O Device
Virtualization

17. CPU Virtualization

18. CPU Virtualization
What is CPU Virtualization?
• Single CPU acting as if there are more than 1 CPU in the
system.
• Most instructions are executed directly on the physical CPU
• The Hypervisor / VMM safely performs privileged instructions

19. X86 Architecture Privileges
• Four Levels of Privileges as Ring
0, 1, 2, 3 for both kernel space
(OS) and user space
applications
• These privileges are meant for
accessing the hardware
resources by the OS and user
space applications
• User Apps run in Ring 3 and OS
runs in Ring 0
• The AMD-V and Intel-VT CPUs
use a new privilege level called
Ring -1 for the VMM

20. Server Virtualization Components
CPU
Virtualization
Full
Virtualization
Bare Metal /
Type1
Hypervisor
Type 2
Hypervisor
Para
Virtualization
Type 2
Hypervisor
Hardware
Assisted
Virtualization
Bare Metal /
Type1
Hypervisor
Type 2
Hypervisor

21. Full Virtualization
User Apps
Guest OS
VMM
System Hardware
Ring 3
Ring 2
Ring 1
Ring 0
Full Virtualization
Requires no hardware assist or OS
assist for virtualization support
Guest OS is not aware of whether it is
running in VM or physical server.
The Guest OS runs in Ring 1 privilege
Hypervisor runs in Ring 0 privilege

22. Bare Metal Execution Methodology
• Guest user apps can’t tamper
with the guest OS due to ring
protections. However user level
code can be directly executed
on the processor for high
performance virtualization.
• Guest user apps and guest OS
can’t tamper with VMM due to
ring protections
• When the guest OS executes a
privileged instruction, it will
trap into the VMM
• When a guest app generates a
system call or exception, the
app will trap into the VMM
• VMM’s trap handler uses a
policy to decide what to do
(e.g., emulate the instruction)
User Apps
Guest OS
VMM
System Hardware
Ring 3
Ring 2
Ring 1
Ring 0
Direct Execution of
virtualizable instructions
Binary Translation of non-
virtualizable instructions
Bare Metal

23. Full Virtualization – Execution Methodology
• Guest user apps can’t tamper
with the guest OS due to ring
protections. However user level
code can be directly executed
on the processor for high
performance virtualization.
• Guest user apps and guest OS
can’t tamper with VMM due to
ring protections
• Any instruction either privileged
or non-privileged will trap into
the VMM
• When a guest app generates a
system call or exception, the
app will trap into the VMM
• VMM’s trap handler uses a
policy to decide what to do
(e.g., emulate the instruction)
User Apps
Guest OS
Host OS
System Hardware
Ring 3
Ring 2
Ring 1
Ring 0
Binary Translation of All
Instructions
Host Based VM

24. Full Virtualization – Drawbacks
Low Performance, typically
in the range of 80 – 97%
Running I/O intensive
applications will be
challenging
Code cache increases the
performance with the cost
of memory

25. Para Virtualization
Para Virtualization
Requires communication between the
guest OS and hypervisor to improve
performance and efficiency
Guest OS should be aware of whether
it is running in VM or physical server
Guest OS kernel needs to be modified
to replace non virtualizable
instructions with hypercalls that
communicate directly with the
hypervisor
The Guest OS runs in Ring 1 privilege.
Hypervisor runs in Ring 0 privilege
User Apps
Guest OS
Instrumented
Host S
System Hardware
Ring 3
Ring 2
Ring 1
Ring 0
Virtualization Layer

26. Para Virtualization – Execution Methodology
• Guest user apps can’t tamper
with the guest OS due to ring
protections. However user level
code can be directly executed
on the processor for high
performance virtualization.
• Guest user apps and guest OS
can’t tamper with VMM due to
ring protections
• As the guest OS kernel is
modified to replace non
virtualizable instructions with
hypercalls that communicate
directly with the hypervisor
• it will issue a hypercall to the
VMM
• VMM’s trap handler uses a
policy to decide what to do
(e.g., execute the instruction)

27. Hardware Assisted Virtualization
Hardware Assisted
Virtualization
Techniques like Intel VT-X, AMD-V
facilitates the hardware assisted
virtualization
Privileged and sensitive calls are set to
automatically trap to the hypervisor
and handled by hardware
The Guest OS runs in Ring 1 privilege
Hypervisor runs in Ring 0 privilege
User Apps
Guest OS
System Hardware
Ring 3
Ring 2
Ring 1
Ring 0
VMMRing -1

28. Multithread Vs Multicore Vs CPU Virtualization

29. Memory Virtualization
What is Memory Virtualization?
• Abstracts the physical memory resources in a virtualized
server.
• Handles the physical memory, virtual memory of both guest
and host OS and maintains mapping between these entities.

30. I/O Virtualization
I/O
Virtualization
Emulated I/O
Para-
virtualized
I/O
Direct I/O

31. Emulated I/O
Guest VM
Guest OS
Host OS
(Linux)
KVM (kernel module)
QEMU
vCPU vCPU
User space
Kernel space
I/O
emulation
I/O operation
MMIO or PIO
Trap
Native drivers
Interrupt
• Software emulates real hardware device
• VMs run same driver for the emulated hardware device
• Trap  hypervisor  I/O emulator (e.g., QEMU)
• Every I/O operation generates trap and emulation
• Poor performance

32. Para-Virtualized I/O
• Split driver model
• Front-end driver in a guest VM
• Virtual driver to forward an I/O request to its back-end driver
• Back-end driver in a host OS
• Request a forwarded I/O to HW via native driver
Guest VM
Guest OS
Host OS
(Linux)
KVM (kernel module)
QEMU
vCPU vCPUUser space
Kernel space
VirtIO
Backend
I/O operation
Native drivers
VirtIO
Frontend
Shared descriptor ring:
Optimization by batching
I/O requests
 Reducing VMM
intervention cost

33. Direct I/O
Guest VM
Guest OS
Host OS
(Linux)
KVM (kernel module)
QEMU
vCPU vCPU
User space
Kernel space
I/O
emulation
I/O operation
MMIO or PIO
Native drivers
33/32
• Directly assign device to Guest
• High performance and low CPU utilization

34. KVM, QEMU, LibVirt

35. Agenda
Introduction
KVM, QEMU, LibVirt
KVM Virtualization
CPU Virtualization in KVM
Memory Virtualization in VM
Para Virtualized Drivers and Network Device Virtualization
Example QEMU, LibVirt commands

36. KVM (Kernel Virtual Machine)
By itself, KVM does not perform any emulation. It exposes
/dev/kvm interface for virtualization
KVM (Kernel VM)
Hardware Assisted Virtualization infra
for linux on X86
Requires hardware containing
virtualization extensions (Intel VT or
AMD-V)
Open Source Software under GPL
license
Two Components: Kernel Component
part of mainline linux for 2.6.20. User
Component (part of Qemu)

37. Why KVM
Hardware Based Virtualization
Native Support for any guest OS
Better Performance
Open Source & Flexible
Enhanced Security

38. KVM

39. QEMU (Quick Emulator)
QEMU (Quick
EMUlator)
Generic and open source machine
emulator and virtualizer
QEMU can run programs made for one
machine (for example: an ARM board)
on a different machine
Hosted hypervisor/VMM that
performs hardware virtualization
Work along with KVM for providing
Hardware Assisted Virtualization

40. Emulation Vs Virtualization
 Both can act as a hypervisor
 Virtualization
 Slice the underlying hardware into multiple disjoint virtual
devices
 The ISA of host and guest typically are same
 Guest operations can be directly dispatched to hardware
 Emulation
 Host and Guest may have different ISA
 Guest ISA is managed in software
 Guest operations needs translation

41. Usage of QEMU
QEMU
Emulation
System
Emulation
Device
Emulation
Virtualization
Standalone KVM

42. KVM vs QEMU
 Both are hypervisors
 Stand alone QEMU uses
paravirtualization where as
KVM provides infra for
hardware virtualization
 KVM virtualizes only CPU
and memory whereas Qemu
virtualizes all other devices
 When QEMU and KVM are
working together we get
hardware assisted
virtualization

43. KVM – Components
 KVM.ko
 Core KVM kernel module
 Implements vCPU and MMU
 Emulates few virtual devices in
kernel
 Provides ioctls for
communications
 Kvm-intel.ko / kvm-amd.ko
 Provide support for Intel VMX
and AMDs SVM support
 qemu-kvm
 Based on Qemu emulator
 Implements much of virtual
devices
 Provides user interface to KVM

44. 44
KVM – High Level Overview

45. 45
KVM – High Level Overview

46. libvirt
Libvirt
Provides Open Source API for
managing the various hypervisors
The management task includes
provision, creation, modification,
monitoring, control, migration etc
Various cloud orchestration platforms
uses libvirt libraries for instantiating
the VMs
Any libvirt client can remotely connect
to the libvirt running in a host server

47. Libvirt and QEMU

48. KVM Virtualization

49. KVM Concepts
 KVM converts the Linux Kernel to provide Hypervisor
support
 However there is no change introduced in the Linux
kernel to provide the Hypervisor support.
 Instead new kernel modules are introduced.
 Linux kernel already does all the process, memory and
i/o management for the process running in the host OS
 KVM introduces a new mode called guest mode along
with the User Mode and Kernel Mode

50. KVM Virtualization
CPU
• CPU Virtualization
Memory
• Memory Virtualization
IO Device
• I/O Virtualization

51. Intel Hardware Support For Virtualization
Intel Virtualization
Support
For processor virtualization, Intel
offers the VT-x . VT-X adds the guest
mode or ring –1 privilege for KVM
For memory virtualization, Intel offers
the EPT, which translates the virtual
address to the machine's physical
addresses to improve performance
For I/O virtualization, Intel
implements VT-d and VT-c

52. CPU Virtualization
 Every VM is a normal application
process in the host machine.
 The VM process in the host machine
can be scheduled to run on the CPU by
the host OS (like normal process).
 However KVM allows the quest code /
OS to run directly into the host CPU
(although the quest OS / code runs as
an application process) using the guest
mode execution
 For scheduling, memory management,
and other services KVM uses the linux
kernel however it helps the user
program to make use of the hardware
virtualization

53. CPU Modes

54. Mode Transitions

55. Virtual Memory Virtualization
 Virtual Memory Virtualization is similar to Virtual Memory concept.
 In virtual memory concept the operating system maintains mappings of
virtual memory to machine memory using page tables.
 However in VM environment, virtual memory virtualization involves
mapping between virtual memory of guest operating system to physical
memory of guest operating system along with the mapping of physical
memory of guest operating system to the machine memory
 The first mapping will be maintained by guest OS and the second
mapping will be maintained by the hypervisor

56. KVM Device Virtualization
Device
Virtualization
Emulation
Para
Virtualization

57. KVM Emulated Device Virtualization
 QEMU in user space provides the emulated device which is a software
implementation of the hardware.
 The guest VM is not aware that it is an emulated device and interacts
with the device
 When there is any I/O operation by the guest VM, the hypervisor
intercepts all I/O requests from the guest operating system and
emulates the operation of the real I/O hardware

58. KVM Para Device Virtualization / VirtIO
 Para-virtualized devices are software implementations of hardware
devices
 Para-virtualization requires that the guest operating system be modified
to communicate with the hypervisor.
 It’s a split driver implementation with front-end driver sitting in VM and
backend driver sitting in KVM
 The frontend and backend drivers communicate through a path that is
nothing but virtio
 The frontend driver manages the I/O requests of the guest OSes and the
backend driver is responsible for managing the real I/O devices and
multiplexing the I/O data of different VMs

59. KVM Para Device Virtualization / VirtIO

60. KVM Network Virtualization
Network
Virtualization
Network
Device
Virtualization
NIC
TUN/TAP
Interface
Bridge OVS
Network
backend
User
Networking
Private Virtual
Bridge
Public Bridge
Routing with
iptables

61. vNIC, TUN/TAP Interface
vNIC
A VNIC is a virtualized Network Interface Card, used by a Virtual Machine as
its network interface.
Linux Bridge
The Linux bridge code implements a subset of the ANSI/IEEE 802.1d standard.
Bridge can be created inside a system and can be used to provide
connectivity across the VM
TAP Interface
TAP simulates a link layer device and it operates with layer 2 packets like
Ethernet frames. Packets sent by an operating system via a TAP device are
delivered to a user-space program which attaches itself to the device
OVS
open-source implementation of a distributed virtual multilayer switch.
Provides a switching stack for hardware virtualization environments

62. KVM Network Virtualization
Network
backend
User
Networking
Private
Virtual Bridge
Public Bridge
Routing with
iptables

63. User Networking
When?
• When the virtual machine is required to access to the host, to internet or to
resources available on your local network.
• There is no need to access your guest from the network or from another guest.
Procedure
• Simply run guest without specifying network parameters, which by default will
create user-level (a.k.a slirp) networking

64. Private Virtual Bridge
When?
• When setting up a private network between 2 or more virtual machines.
• This network won't be seen from the other virtual machines nor from the real
network.
Procedure
• Create a bridge
• Create a tap device
• Attach the tap device to the bridge

65. Public Bridge
When?
• You want to assign IP
addresses to your virtual
machines and make them
accessible from your local
network
Procedure
• Create a bridge
• Create a tap device
• Attach the tap device to the
bridge
• Attach the host machine
interface to the bridge

66. Routing With IP Tables
When?
• You want to pass through
all the traffic from VM to
IP tables of Host
Procedure
• Create a bridge
• Create a tap device
• Attach the tap device to
the bridge
• Attach the host machine
interface to the bridge

67. VirtIO Example (Packet IO)

68. Handson

69. KVM Installation
 Check your CPU has hardware virtualization
support – either Intel VT-x or AMD-V.
 egrep -c ‘(svm|vmx)’ /proc/cpuinfo should return a value 1 or more
 Install KVM, lib-virt, linux bridge utilities and GUI
based virt-manager
 sudo apt-get install qemu-kvm libvirt-bin bridge-utils virt-manager
 Run the command to add your user account to
the libvirt group
 sudo adduser name libvirtd

70. Basic QEMU-KVM CLI Commands
 qemu-kvm options disk_img
 qemu-kvm -name “Telsites" -M pc-0.12 -m 512 -cpu kvm64 -smp 2
/images/telsitessp1.raw
 qemu-kvm -hda /images/selsitessp1.raw -net nic -net user
 qemu-kvm -hda /images/imagei1.raw -hdb /images/image2.raw -hdc
/images/image3.raw -hdd /images/image4.raw

71. Thank you
kingstonsmiler@gmail.com