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, 10 years after the project started, 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, common challenges for KVM and Xen and securing the cloud. It will introduce concepts such as the virtualization spectrum, the concept of domain disaggregation and the Xen Security Modules as techniques to increase security, robustness and scalability. All important factors for building clouds at scale. The talk will conclude with exciting developments in the Xen community, such as Xen support for ARM servers, Mirage appliances that can be run on any Xen based cloud, etc. and explore their implications for building open source clouds.

1. Lars Kurth
Xen Project Community Manager
lars.kurth@xen.org
10 Years of Xen and beyond …
@lars_kurth
FREENODE: lars_kurth

2. • Teams aka sub-projects
– Hypervisor
– XAPI
– ARM Hypervisor (for Servers as well as Mobile Devices)
– Mirage OS
• Governance : mixture between Linux Kernel and Apache
– Consensus decision making
– Sub-project life-cycle (aka incubator)
– PMC style structure for team leadership
– Funded by member companies (Advisory Board)
Xen.org becomes XenProject.org

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

4. Hypervisor Architecture

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

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

7. Xen: Type 1 with a Twist
Type 1: Bare metal Hypervisor
Host HW
Memory CPUsI/O
HypervisorScheduler
MMUDevice Drivers/Models
VMn
VM1
VM0
Guest OS
and Apps

8. Xen: Type 1 with a Twist
Type 1: Bare metal Hypervisor
Host HW
Memory CPUsI/O
HypervisorScheduler
MMUDevice Drivers/Models
VMn
VM1
VM0
Guest OS
and Apps
Host HW
Memory CPUsI/O
Hypervisor
VMn
VM1
VM0
Guest OS
and Apps
Xen Architecture
Scheduler MMU

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

10. Xen Project 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

11. Basic Xen Concepts
11
Control domain
(dom0)
Host HW
VMn
VM1
VM0
Guest OS
and Apps
Memory CPUsI/O
Console
• Interface to the outside world
Control Domain aka Dom0
• Dom0 kernel with drivers
• Xen Management Toolstack
Guest Domains
• Your apps
Driver/Stub/Service Domain(s)
• A “driver, device model or control
service in a box”
• De-privileged and isolated
• Lifetime: start, stop, kill
Dom0 Kernel
HypervisorScheduler MMU XSM
Trusted Computing Base

12. Basic Xen Concepts
12
Control domain
(dom0)
Host HW
VMn
VM1
VM0
Guest OS
and Apps
Console
Memory CPUsI/O
Dom0 Kernel
Toolstack
HypervisorScheduler MMU XSM
Console
• Interface to the outside world
Control Domain aka Dom0
• Dom0 kernel with drivers
• Xen Management Toolstack
Guest Domains
• Your apps
Driver/Stub/Service Domain(s)
• A “driver, device model or control
service in a box”
• De-privileged and isolated
• Lifetime: start, stop, kill
Trusted Computing Base

13. Basic Xen Concepts
13
Control domain
(dom0)
Host HW
VMn
VM1
VM0
Guest OS
and Apps
Console
Memory CPUsI/O
One or more
driver, stub or
service domains
Dom0 Kernel
Toolstack
HypervisorScheduler MMU XSM
Console
• Interface to the outside world
Control Domain aka Dom0
• Dom0 kernel with drivers
• Xen Management Toolstack
Guest Domains
• Your apps
Driver/Stub/Service Domain(s)
• A “driver, device model or control
service in a box”
• De-privileged and isolated
• Lifetime: start, stop, kill
Trusted Computing Base

14. 14
Xen Variants for Server & Cloud
Xen HypervisorHypervisor

15. Single Host
Basic Functions
Multiple Hosts
Additional Functionality
15
Xen Variants for Server & Cloud
Increased level of functionality and integration with other components
Default / XL (XM)Toolstack / Console Libvirt / VIRSH XAPI / XE
Hypervisor
Single Host
Additional Functionality
Xen Hypervisor

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

17. 17
Xen Variants for Server & Cloud
Increased level of functionality and integration with other components
Default / XL (XM)Toolstack / Console Libvirt / VIRSH
Products Oracle VM Huawei UVP Citrix XenServer
Project
XAPI / XE
Xen Hypervisor

18. 18
Xen Variants for Server & Cloud
Increased level of functionality and integration with other components
Default / XL (XM)Toolstack / Console Libvirt / VIRSH
Used by …
Project
XAPI / XE
Products Oracle VM Huawei UVP Citrix XenServer
Xen Hypervisor

19. Xen : Types of Virtualization

20. 20
Xen Hypervisor
Control domain
(dom0)
Host HW
Guest VMn
Apps
Memory CPUsI/O
Technology:
• Paravirtualization
Linux PV guests have limitations:
• limited to a subset of set of virtual HW
Advantages
• Fast
• Works on any system
(even without virt extensions)
HW Drivers
PV Back Ends PV Front Ends
Guest OSDom0 Kernel
PV Domains

21. 21
Xen Hypervisor
Control domain
(dom0)
Host HW
Guest VMn
Apps
Memory CPUsI/O
Technology:
• Paravirtualization
Linux PV guests have limitations:
• limited to a subset of virtual HW
Advantages
• Fast
• Works on any system
(even without virt extensions)
Driver Domains
• Security
• Isolation
• Reliability and Robustness
HW Drivers
PV Back Ends PV Front Ends
Driver Domain
e.g.
• Disk
• Network
HW Driver
PV Back End
Dom0 Kernel*
*) Can be MiniOS
Guest OSDom0 Kernel
PV Domains & Driver Domains

22. 22
Xen Hypervisor
Dom0
Host HW
Guest VMn
Technology:
• Shows emulation using QEMU/Device
Model (SW Virtualization)
• In other situation HW can be used
Disadvantages
• Emulation slower than PV
(mainly I/O devices)
Advantages
• No kernel support needed
Device Model
IO Emulation
IO Event
VMEXITDom0 Kernel
HVM & Stub Domains
Memory CPUsI/O

23. 23
Xen Hypervisor
Dom0
Host HW
Guest VMn
Technology:
• Shows emulation using QEMU/Device
Model (SW Virtualization)
• In other situation HW can be used
Disadvantages
• Emulation slower than PV
(mainly I/O devices)
Advantages
• No kernel support needed
Stub Domains
• Security
• Isolation
• Reliability and Robustness
Device Model
IO Emulation
IO Event
VMEXIT
Stubdomn
Device Model
Mini OS
Guest VMn
IO Emulation
IO Event
VMEXITDom0 Kernel
HVM & Stub Domains
Memory CPUsI/O

24. The Virtualization Spectrum
Fully Virtualized (FV) VS VS VS VH
FV with PV for disk & network P VS VS VH
PVHVM P P VS VH
PVH P P P VH
Fully Paravirtualized (PV) P P P P
VH Virtualized (HW)
P Paravirtualized
VS Virtualized (SW)
HVM mode/domain
PV mode/domain
Xen 4.4

25. The Virtualization Spectrum
Fully Virtualized (FV) VS VS VS VH
FV with PV for disk & network P VS VS VH
PVHVM P P VS VH
PVH P P P VH
Fully Paravirtualized (PV) P P P P
Scope for improvement
Poor performance
Optimal performance
HVM mode/domain
Xen 4.4
PV mode/domain

26. The Virtualization Spectrum
Fully Virtualized (FV) VS VS VS VH
FV with PV for disk & network P VS VS VH
PVHVM P P VS VH
PVH P P P VH
Fully Paravirtualized (PV) P P P P
Scope for improvement
Poor performance
Optimal performance
HVM mode/domain
Xen 4.4
PV mode/domain
Important: Xen automatically picks the best
option based on HW & OS capabilities and
available drivers.
As a Xen user I chose a HVM or PV domain.

27. Single Host
Basic Functions
Multiple Hosts
Additional Functionality
XAPI, XCP and XCP-XAPI : What is it?
Increased level of functionality and integration with other components
Default / XL (XM)Toolstack / Console Libvirt / VIRSH XAPI / XE
Hypervisor
Single Host
Additional Functionality
Xen Hypervisor

28. XAPI : What do I get?
Multiple Hosts
Additional Functionality
XAPI / XE
Xen Hypervisor
• VM lifecycle: live snapshots, checkpoint, migration
• Storage XenMotion: Migrate VMs between hosts or pools
without shared storage (while the VM is running)
• Resource pools: flexible storage and networking
• Event tracking: progress, notification
• Upgrade and patching capabilities
• Real-time performance monitoring and alerting
• Templates for Windows and Linux guests
• Open vSwitch support built-in (default)
More info: wiki.xen.org/wiki/XCP_Release_Features

29. XAPI : two variants!
Multiple Hosts
Additional Functionality
XAPI / XE
Xen Hypervisor
XCP ISO (at v1.6)
Xen 4.1.3 + XAPI
CentOS 5.3
Kernel (v2.6.32.43)
OVS 1.4.2
XCP-XAPI packages
Debian Wheezy
Ubuntu 12.04 LTS
Others in progress …

30. XAPI : Orchestration and UIs
Multiple Hosts
Additional Functionality
XAPI / XE
Xen Hypervisor

31. Other XEN Cloud Orchestration
Single Host
Basic Functions
XM or XL
Xen Hypervisor
Single Host
Additional Functionality
Libvirt
Xen Hypervisor

32. Challenges for FOSS hypervisors

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

34. System characteristics cloud users care about:
“Robustness, Performance, Scalability & Security”
Results XCP User Survey 2013 – 90% of users quoted these as most important attributes

35. 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 XAPI
Disaggregation
See qubes-os.org
Different windows run
in different VMs

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

37. Next: XAPI Architecture Diagram
Before and After Disaggregation

38. CPUCPU
RAM RAMNIC
(or SR-
IOV VF)
NIC
(or SR-
IOV VF)
NIC
(or SR-
IOV VF)
NIC
(or SR-
IOV VF)
RAID
Xen
Dom0Network
drivers
NFS/
iSCSI
drivers
Qemu xapi Local
storage
drivers
NFS/
iSCSI
drivers
Network
drivers
Qemu
eth eth eth eth scsi
User VM User VM
NB gntdev NB
NF BF NF BF
qemu qemu
xapi
vswitch
networkd
tapdisk
blktap3
storaged
syslogd
vswitch
networkd
tapdisk
blktap3
storaged
tapdisk
blktap3
storaged
gntdev gntdev
Dom0
xenopsd
libxl
healthd
Domain
manager
Dom0
.
.
.
.
Xen
xapi

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

40. 40
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

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

42. 42
Xen Advanced Security Recipes
• Xen has many Security Features (besides the ones I covered)
• Most are not switched on by default
• Although most are simple to use, some seen complicated
See: http://www.slideshare.net/xen_com_mgr/
a-brief-tutorial-on-xens-advanced-security-features
And more are be coming!

43. ARM Hypervisor

44. Xen on ARM
• by Stefano Stabellini –
Xen and Xen-ARM Linux maintainer
• New York III from 10:45 to 11:30
• Including a demo
In depth presentation tomorrow …
One mode to
rule them all

45. Mirage OS

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

47. • Recently added to Xen Project incubator
• In beta stage : first release on its way (July 2013)
• Clean-slate protocols implementations, e.g.
– TCP/IP, DNS, SSH, Openflow (switch/controller), HTTP, XMPP, ...
– New applications using next generation XAPI
(disaggregated XAPI architecture)
Mirage OS
More info: http://www.slideshare.net/xen_com_mgr/
mirage-extreme-specialisation-of-virtual-appliances

48. Hot Topics and Projects

49. • Release candidates & Xen Test Days (today, June 5th)
• Xen ARM for Servers
• Extend scope of Xen Security Modules
• Default to QEMU upstream
• Updated and improved libvirt drivers for Xen
• Lots of other stuff:
– scalability, performance, better NUMA support, …
Xen 4.3 Release (June 2013)
More info: http://lists.xen.org/archives/html/xen-devel/2013-05/msg01134.html

50. “For about a year members of the Xen Project, the CentOS community
and large Xen Users have worked on bringing Xen and XAPI to
CentOS 6”
Driven by demand from the community :
• Can run Xen on CentOS 6 today, but non-trivial
• We wanted “YUM INSTALL XEN”
• Mostly a packaging problem
• Teams from CentOS, Citrix, Go Daddy & Rackspace
• QA and usability sanity checks
Xen 4 + XAPI in CentOS 6 (June 2013)

51. “Growth is leading to more structure & more collaboration & more openness!”
• Establishing a shared and open test infrastructure
– Goal: Increase development velocity
• Improved usability and better distro-integration
– Xen + XAPI in CentOS 6.4
• More focus on downstreams
– OpenStack and Xen Orchestra
– Better libvirt and virt-manager integration
• Changing the XAPI / XCP release model
• Xen on ARM and collaboration with Linaro
The Xen Community is Changing

52. Online : xenproject.org > User & Help menus
• Mailing Lists and IRC
• Q&A System
• Find me and I can get you hooked up!
Events : xenproject.org/about/events.html
• Test Days (IRC at #xentest) … today, June 5th
• Document Days (IRC at #xendocs) … the next one is May 28th
• User (Sept 18, New Orleans) and Developer Summits (Oct 24-25, Edinburgh)
• Hackathons - last week search for “[Hackathon Minutes]” on xen-devel
Getting Started with Xen Projects

53. Thank You!
Slides available under CC-BY-SA 3.0
From www.slideshare.net/xen_com_mgr
@lars_kurth
FREENODE: lars_kurth
• News: blog.xenproject.org
• Web: xenproject.org > Help
– Help for IRC, Lists, …
– Stackoverflow like Q&A
• Wiki: wiki.xenproject.org
• Presentations: slideshare.net/xen_com_mgr
• Videos: vimeo.com/channels/xen