The Xen Hypervisor was built for the Cloud from the outset: when Xen was designed, we anticipated a world, which today is known as cloud computing. Today, Xen powers the largest clouds in production. This talk explores success criteria, architecture, trade-offs and challenges for cloudy hypervisors. It is intended for users and developers and starts with a brief introduction to Xen and XCP, their architecture and on common challenges for KVM and Xen. I will introduce the concept of domain disaggregation as an approach to increase security, robustness and scalability: all important factors for building clouds at scale and show how advanced security features suchas Xen Security Modules and SELinux can help secure your cloud further. The talk will conclude with exciting developments in the Xen community, such as Xen for ARM servers, a new virtualization mode for Xen, running applications without OS in a Xen guest and point out their implications for building open source clouds.

1. Virtualization in the Cloud:
Featuring Xen and XCP
Lars Kurth
Xen Community Manager
lars.kurth@xen.org
FREENODE: lars_kurth @lars_kurth

2. A Brief History of Xen in the Cloud
Late 90s
XenoServer
Project

3. A Brief History of Xen in the Cloud
Late 90s ‘03
XenoServer
Project
Xen 1.0

4. A Brief History of Xen in the Cloud
Late 90s ‘03 ‘06 ‘08
XenoServer Amazon EC2
Project and Slicehost
launched
Xen 1.0 Rackspace
Cloud

5. A Brief History of Xen in the Cloud
Late 90s ‘03 ‘06 ‘08 ‘11 ‘12
XenoServer Amazon EC2 XCP 1.x
Project and Slicehost Cloud Mgmt
launched
Xen 1.0 Rackspace
Cloud
XCP packages
in Linux

6. A Brief History of Xen in the Cloud
Late 90s ‘03 ‘06 ‘08 ‘11 ‘12
XenoServer Amazon EC2 XCP 1.x
Project and Slicehost Cloud Mgmt
launched
Xen 1.0 Rackspace Linux 3.0
Cloud
XCP packages
in Linux

7. A Brief History of Xen in the Cloud
Late 90s ‘03 ‘06 ‘08 ‘11 ‘12 ‘13
XenoServer Amazon EC2 XCP 1.x
Project and Slicehost Cloud Mgmt
launched
Xen 1.0 Rackspace Linux 3.0 Xen for
Cloud ARM servers
XCP packages
in Linux
10th
birthday

8. The Xen Hypervisor was designed for
the Cloud straight from the outset!

9. Xen.org
• Guardian of Xen Hypervisor and related OSS Projects
• Xen Governance similar to Linux Kernel
– Plus project lifecycle and Project Management Committee (PMC)
• Projects
– Xen Hypervisor
(led by 5 committers, 2 from Citrix, 1 from Suse, 2 Independent)
– Xen Cloud Platform aka XCP (led by Citrix)
– Xen ARM : Xen for mobile devices (led by Samsung)

10. Xen contributor community is diversifying
100%
90%
• The number of “significant”
80% active vendors is increasing
70%
60%
50% • New feature development driving
40%
30%
new participation
20%
10%
0%
2010 2011 2012
Citrix UPC
SUSE Amazon
University AMD
GridCentric Individual
NSA Intel
Fujitsu iWeb
Misc Oracle
Spectralogic University of British Columbia

11. Xen Overview

12. Hypervisor Architectures
Type 1: Bare metal Hypervisor
A pure Hypervisor that runs directly on the
hardware and hosts Guest OS’s.
VMn
VM1
VM0
Guest OS
and Apps
Scheduler Hypervisor
Device Drivers/Models MMU
Host HW
I/O Memory CPUs
Provides partition isolation + reliability,
higher security

13. Hypervisor Architectures
Type 1: Bare metal Hypervisor Type 2: OS ‘Hosted’
A pure Hypervisor that runs directly on the A Hypervisor that runs within a Host OS and hosts
hardware and hosts Guest OS’s. Guest OS’s inside of it, using the host OS services
to provide the virtual environment.
VMn User-level VMM VMn
VM1 User
VM1
Apps
VM0 Device Models
VM0
Guest OS Guest OS
and Apps and Apps
Host OS
Scheduler Hypervisor
Ring-0 VM Monitor
Device Drivers/Models Device Drivers “Kernel “
MMU
Host HW Host HW
I/O Memory CPUs I/O Memory CPUs
Provides partition isolation + reliability, Low cost, no additional drivers
higher security Ease of use & installation

14. Xen: Type 1 with a Twist
Type 1: Bare metal Hypervisor
VMn
VM1
VM0
Guest OS
and Apps
Scheduler Hypervisor
Device Drivers/Models MMU
Host HW
I/O Memory CPUs

15. Xen: Type 1 with a Twist
Type 1: Bare metal Hypervisor Xen Architecture
VMn
VM1 VMn
VM0 VM1
Guest OS VM0
and Apps
Guest OS
and Apps
Scheduler Hypervisor
Device Drivers/Models MMU Scheduler MMU Hypervisor
Host HW Host HW
I/O Memory CPUs I/O Memory CPUs

16. Xen: Type 1 with a Twist
Type 1: Bare metal Hypervisor Xen Architecture
Control domain
(dom0)
VMn
VM1 Device Models VMn
VM0 VM1
Guest OS VM0
and Apps Drivers
Guest OS
Linux & BSD and Apps
Scheduler Hypervisor
Device Drivers/Models MMU Scheduler MMU Hypervisor
Host HW Host HW
I/O Memory CPUs I/O Memory CPUs

17. Xen and Linux
• Xen Hypervisor is not in the Linux kernel
• BUT: everything Xen and Xen Guests need to run is!
• Xen packages are in all Linux distros (except RHEL6)
– Install Dom0 Linux distro
– Install Xen package(s) or meta package
– Reboot
– Config stuff: set up disks, peripherals, etc.
More info: wiki.xen.org/wiki/Category:Host_Install

18. Basic Xen Concepts
Console
• Interface to the outside world
Control Domain aka Dom0
VMn
• Dom0 kernel with drivers
Control domain VM1
(dom0) • Xen Management Toolstack
VM0
Guest OS
Guest Domains
Dom0 Kernel and Apps • Your apps
Scheduler MMU XSM Hypervisor Driver/Stub/Service Domain(s)
• A “driver, device model or control
Host HW service in a box”
I/O Memory CPUs
• De-privileged and isolated
• Lifetime: start, stop, kill
Trusted Computing Base 18

19. Basic Xen Concepts
Console
Console • Interface to the outside world
Control Domain aka Dom0
VMn
• Dom0 kernel with drivers
Control domain VM1
(dom0) • Xen Management Toolstack
VM0
Toolstack
Guest OS
Guest Domains
Dom0 Kernel and Apps • Your apps
Scheduler MMU XSM Hypervisor Driver/Stub/Service Domain(s)
• A “driver, device model or control
Host HW service in a box”
I/O Memory CPUs
• De-privileged and isolated
• Lifetime: start, stop, kill
Trusted Computing Base 19

20. Basic Xen Concepts
Console
Console • Interface to the outside world
Control Domain aka Dom0
VMn
• Dom0 kernel with drivers
Control domain VM1
(dom0) • Xen Management Toolstack
One or more VM0
Toolstack driver, stub or
service domains Guest OS
Guest Domains
Dom0 Kernel and Apps • Your apps
Scheduler MMU XSM Hypervisor Driver/Stub/Service Domain(s)
• A “driver, device model or control
Host HW service in a box”
I/O Memory CPUs
• De-privileged and isolated
• Lifetime: start, stop, kill
Trusted Computing Base 20

21. Xen Variants for Server & Cloud
Hypervisor Xen
21

22. Xen Variants for Server & Cloud
Hypervisor Xen
Toolstack / Console Default / XL (XM) Libvirt / VIRSH XAPI / XE
Increased level of functionality and integration with other components
Single Host Single Host
Basic Functions Additional Functionality
Multiple Hosts
Additional Functionality
22

23. Xen Variants for Server & Cloud
Hypervisor Xen XCP
Toolstack / Console Default / XL (XM) Libvirt / VIRSH XAPI / XE
Increased level of functionality and integration with other components
Single Host Single Host
Basic Functions Additional Functionality
Multiple Hosts
Additional Functionality
23

24. Xen Variants for Server & Cloud
Project Xen XCP
Toolstack / Console Default / XL (XM) Libvirt / VIRSH XAPI / XE
Increased level of functionality and integration with other components
Get Binaries from … Linux Distros Linux Distros Debian & Ubuntu
ISO from Xen.org
24

25. Xen Variants for Server & Cloud
Project Xen Hypervisor XCP
Toolstack / Console Default / XL (XM) Libvirt / VIRSH XAPI / XE
Increased level of functionality and integration with other components
Get Binaries from … Linux Distros Linux Distros Debian & Ubuntu
ISO from Xen.org
Products Oracle VM Huawei UVP Citrix XenServer
25

26. Xen Variants for Server & Cloud
Project Xen Hypervisor XCP
Toolstack / Console Default / XL (XM) Libvirt / VIRSH XAPI / XE
Increased level of functionality and integration with other components
Get Binaries from … Linux Distros Linux Distros Debian & Ubuntu
ISO from Xen.org
Used by …
More info: xen.org/community/ecosystem.html
xen.org/community/presentations.html
26
xen.org/products/case_studies.html

27. Xen : Types of Virtualization

28. PV Domains
Technology:
Control domain Guest VMn
(dom0) • Paravirtualization
Apps Linux PV guests have limitations:
• limited set of virtual hardware
PV Back Ends PV Front Ends
Advantages
HW Drivers • Fast
Dom0 Kernel Guest OS
• Works on any system
(even without virt extensions)
Xen Hypervisor
Host HW
I/O Memory CPUs
28

29. PV Domains & Driver Domains
Technology:
Control domain Guest VMn Driver Domain
(dom0) e.g. • Paravirtualization
• Disk
Apps
• Network
Linux PV guests have limitations:
• limited set of virtual hardware
PV Back Ends PV Front Ends PV Back End
Advantages
HW Drivers HW Driver • Fast
Dom0 Kernel Guest OS Dom0 Kernel*
• Works on any system
(even without virt extensions)
Xen Hypervisor Driver Domains
• Security
Host HW • Isolation
I/O Memory CPUs
• Reliability and Robustness
*) Can be MiniOS
29

30. HVM & Stub Domains
Technology:
Dom0 Guest VMn
• Shows emulation using QEMU/Device
Model
IO Emulation
(SW Virtualization)
Device Model • In other situation HW can be used
Disadvantages
IO Event
• Emulation slower than PV
Dom0 Kernel VMEXIT (mainly I/O devices)
Xen Hypervisor Advantages
• No kernel support needed
Host HW
I/O Memory CPUs
30

31. HVM & Stub Domains
Technology:
Dom0 Guest VMn Stubdomn Guest VMn
• Shows emulation using QEMU/Device
Model
IO Emulation IO Emulation
(SW Virtualization)
Device Model Device Model • In other situation HW can be used
Disadvantages
IO Event IO Event
• Emulation slower than PV
Dom0 Kernel VMEXIT Mini OS VMEXIT (mainly I/O devices)
Xen Hypervisor Advantages
• No kernel support needed
Host HW Stub Domains
I/O Memory CPUs
• Security
• Isolation
• Reliability and Robustness
31

32. The Virtualization Spectrum
VS Virtualized (SW)
VH Virtualized (HW)
P Paravirtualized
Fully Virtualized (FV) VS VS VS VH
FV with PV for disk & network P VS VS VH HVM mode/domain
PVHVM P P VS VH
PVH Xen 4.3 P P P VH
PV mode/domain
Fully Paravirtualized (PV) P P P P

33. The Virtualization Spectrum
Optimal performance
Scope for improvement
Poor performance
Fully Virtualized (FV) VS VS VS VH
FV with PV for disk & network P VS VS VH HVM mode/domain
PVHVM P P VS VH
PVH Xen 4.3 P P P VH
PV mode/domain
Fully Paravirtualized (PV) P P P P

34. The Virtualization Spectrum
Important: Xen automatically picks the best
option based on HW & OS capabilities and
Optimal performance available drivers.
As a Xen user I chose a HVM or PV domain.
Scope for improvement
Poor performance
Fully Virtualized (FV) VS VS VS VH
FV with PV for disk & network P VS VS VH HVM mode/domain
PVHVM P P VS VH
PVH Xen 4.3 P P P VH
PV mode/domain
Fully Paravirtualized (PV) P P P P

35. XCP Project

36. XCP – Xen Cloud Platform
Complete stack for server virtualization
• Extends Xen to cover multiple hosts
• Adds further functionality and integrations
for cloud, storage and networking to Xen HV
• GPLv2
• XenServer is a commercial XCP distro
Two Flavours
• Appliance (ISO using CentOS Dom0)
• Packages in Debian & Ubuntu
(more distros to come)

37. Major XCP Features
• VM lifecycle: live snapshots, checkpoint, migration
• Resource pools: flexible storage and networking
• Event tracking: progress, notification
• Upgrade and patching capabilities
• Real-time performance monitoring and alerting
• Built-in support and templates for Windows and Linux guests
• Open vSwitch support built-in (default)
More info: wiki.xen.org/wiki/XCP_Release_Features

38. XCP 1.6
• New format Windows drivers:
installable by Windows Update Service
• Networking: Better VLAN scalability, LACP bonding, IPv6
• Storage XenMotion:
– Migrate VMs between hosts or pools without shared storage
– Move a VM’s disks between storage repositories while the VM is running
• Other: more templates, latest Xen, OVS, etc.
More info: xen.org/download/xcp/releasenotes_1.6.0.html &
More info: xen.org/download/xcp/index_1.6.0.html

39. XCP and Cloud Orchestration Stacks

40. Challenges for FOSS hypervisors

41. “Security and QoS/Reliability are amongst
the top 3 blockers for cloud adoption”
www.colt.net/cio-research

42. System characteristics cloud users care about:
“Robustness, Performance, Scalability & Security”
Results XCP User Survey 2012 – 90% of users quoted these as most important attributes

43. Disaggregation
Split Control Domain into Driver,
Stub and Service Domains
– See: ”Breaking up is hard to do” @ Xen Papers
– See: “Domain 0 Disaggregation for XCP and XenServer”
Used today by Qubes OS and Citrix XenClient XT
Prototypes for XCP
See qubes-os.org
Different windows run
in different VMs

44. Benefits of Disaggregation
More Security
Increased serviceability and flexibility
Better Robustness
Better Performance Ability to safely restart parts of the system
(e.g. just 275ms outage from failed Ethernet driver)
Better Scalability

45. Next: XCP Architecture Diagram
Before and After Disaggregation

46. User VM User VM
NF BF NF BF
NB gntdev NB gntdev gntdev
Dom0 Network NFS/
Dom0 Qemu xapi Qemu Network NFS/ Local
drivers iSCSI drivers iSCSI storage
Domain
manager
drivers . drivers drivers
qemu
. qemu
healthd storaged storaged storaged
networkd . networkd
xenopsd tapdisk syslogd . tapdisk tapdisk
libxl vswitch blktap3 vswitch blktap3 blktap3
xapi xapi
eth eth
Dom0 eth eth scsi
Xen Xen
CPU CPU
NIC NIC RAM RAM NIC NIC
(or SR- (or SR- (or SR- (or SR- RAID
IOV VF) IOV VF) IOV VF) IOV VF)

47. User VM User VM
NF BF NF BF
NB gntdev NB gntdev gntdev
Dom0 Network NFS/ Qemu xapi D Logging Network NFS/ Local
driver iSCSI domain domain domain driver iSCSI storage
Domain o
manager
domain driver
m
. domain driver driver
domain domain domain
healthd storaged
qemu 0 . storaged storaged
networkd networkd
xenopsd tapdisk
. tapdisk tapdisk
libxl vswitch blktap3 xapi syslogd vswitch blktap3 blktap3
dbus over v4v dbus over v4v
eth eth eth eth scsi
Xen Xen
CPU CPU
NIC NIC RAM RAM NIC NIC
(or SR- (or SR- (or SR- (or SR- RAID
IOV VF) IOV VF) IOV VF) IOV VF)

48. Xen Security Advantages
• Even without Advanced Security Features
– Well-defined trusted computing base (much smaller than on type-2 HV)
– Minimal services in hypervisor layer
• Xen Security Modules (or XSM) and FLASK
– XSM is Xen equivalent of LSM
– FLASK is Xen equivalent of SELinux
– Developed, maintained and contributed to Xen by NSA
– Compatible with SELinux (tools, architecture)
– XSM object classes maps onto Xen features
More info: http://www.slideshare.net/xen_com_mgr/
a-brief-tutorial-on-xens-advanced-security-features
50

49. User VM User VM
NF BF NF BF
NB gntdev NB gntdev gntdev
Dom0 Network NFS/ Qemu xapi D Logging Network NFS/ Local
driver iSCSI domain domain domain driver iSCSI storage
Domain o
manager
domain driver
m . domain driver driver
domain domain domain
healthd storaged
qemu 0 . storaged storaged
networkd networkd
xenopsd tapdisk
. tapdisk tapdisk
libxl vswitch blktap3 xapi syslogd vswitch blktap3 blktap3
dbus over v4v dbus over v4v
eth eth eth eth scsi
FLASK policy
restricting access Xen Xen
CPU CPU
NIC NIC RAM RAM NIC NIC
(or SR- (or SR- (or SR- (or SR- RAID
IOV VF) IOV VF) IOV VF) IOV VF)

50. News from the Xen Community

51. Coming in Xen 4.3 (Q2 2013)
• PVH virtualization mode
• Extend scope of Xen Security Modules
• qxl Spice support for 3d acceleration
• Updated and improved libvirt drivers for Xen
• Lots of other stuff:
– scalability, performance, better NUMA support, …
More info: blog.xen.org/index.php/2013/02/11/xen-4-3-mid-release-roadmap-update

52. Xen 4.3 for ARM Servers
Fully functional for ARM v7 & v8
ARM v7: Versatile Express, Arndale &
Samsung Chromebook
ARM v8: Fast Model

53. Xen and ARM : a perfect Match
ARM SOC ARM Architecture Features for Virtualization
User mode : EL0
Device Tree describes …
Kernel mode : EL1
I/O
Hypercall interface :HVC
GIC 2 stage
GT
v2 MMU Hypervisor mode : EL2

54. Xen and ARM : a perfect Match
ARM SOC ARM Architecture Features for Virtualization
Dom0 Any Xen Guest VM (including Dom0)
only EL0
Device Tree describes … User Space
Kernel
EL1
I/O
HVC
GIC 2 stage
GT
v2 MMU EL2
Xen Hypervisor

55. One mode to rule them all
Optimal performance
Scope for improvement
x86: PVHVM P P VS VH HVM mode/domain
x86: PVH P P P VH PV mode/domain
ARM v7 & v8 P VH VH VH

56. Xen in CentOS 6.4+
Xen is coming back to CentOS
In semi-private beta
Planned release in CentOS 6.4
Include XAPI packages – aka XCP in CentOS

57. Xen Library Operating Systems
Application stacks only running on Xen APIs
Control domain Guest VMn
Works on any Xen based cloud or hosting service (dom0)
Apps
Examples
PV Back Ends
– ErlangOnXen.org : Erlang Library OS
embedded
– HalVM : Haskell HW Drivers in Language
run-time
– OpenMirage : Ocaml Dom0 Kernel
Benefits: Xen
– Small footprint Host HW
– Low startup latency
– Extremely fast migration of VMs

58. Summary: Why Xen?

59. • Designed for the Cloud : many advantages for cloud use!
– Resilience, Robustness & Scalability
– Security: Small surface of attack,
Isolation & Advanced Security Features
• Widely used by Cloud Providers and Vendors
• XCP
– Ready for use with cloud orchestration stacks
• Open Source with a large community and eco-system
– Xen is still on top of the game
– Exciting new developments and features in the pipeline

60. • IRC: ##xen @ FREENODE
• Mailing List: xen-users & xen-api (lists.xen.org)
• Wiki: wiki.xen.org
• Ecosystem pages:
xen.org/community/ecosystem.html
• Presentations & Videos:
xen.org/community/presentations.html
Thank You! @lars_kurth
FREENODE: lars_kurth
Slides available under CC-BY-SA 3.0
From www.slideshare.net/xen_com_mgr