Slides from the presentation by Russell Pavlicek to the Frontier Big Data Virtualization Cloud Meetup from Oct 14, 2013 in Mountain View, CA.

1. Xen: FOSS Hypervisor for the Cloud
Russell Pavlicek
Xen Project Evangelist
Russell.Pavlicek@XenProject.org
@RCPavlicek

2. So Who’s the Fat Geek up Front?

3. About the Speaker...
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Linux user since 1995; Linux desktop since 1997
Linux advocate before I ever saw the software
Early Linux advocate at Digital Equipment Corporation, Compaq
Former FOSS columnist for Infoworld, Processor magazines
Former panelist on The Linux Show webcast
Wrote book, Embracing Insanity: Open Source Software Development (2000)
Speaker at 50+ Open Source conferences
Became Xen Project Evangelist employed by Citrix in January 2013
Formerly with Cassatt Corporation in San Jose, cloud startup (2004-2009)

4. A Word About the Xen Stack
• The main components:
– Xen Hypervisor, the central FOSS project
– Xen API, the Cloud enabled subproject
• Better known as “XAPI”
– Xen Project is a Linux Foundation Collaborative Project
– These are the subjects of this talk
• And then there’s:
– XenServer, a popular Xen-based product
• Was partially closed source; recently open-sourced by Citrix

5. The Cloud “Problem”

6. IT: Pre-Cloud
• Stability is Paramount
– The value of IT to the corporation is consistent service availability
– Service capacity specified a year or more in advance
– What’s up, stays up
• Change is Bad
– Change to status quo is disruptive and dangerous
– Changes are beaten into submission until they become part of
the new status quo – and then they are no longer changes

7. IT in the Cloud
• Availability of Services is Paramount
– The value of IT to the corporation is consistent service availability
at levels matching dynamic business demand
– Service capacity must move with business needs
– What’s up when depends on what’s needed when
• Change is Good
– Services must change to cover the needs of the moment
– Lack of change = lack of value

8. Layers of the Cloud
App
Operating System Layer
Virtualization Layer
Cloud Orchestration Layer

9. Virtualization in the Cloud
• It must be stable
• It must be secure
• It must be configurable on a large scale
– The “user at machine” paradigm does not work
– If it requires a mouse, you’re in trouble
• It must take orchestration (APIs, command line)
• It must be multi-tenant
• It must not lock you into one concept or provider of Cloud

10. Xen: Stable
• Solid track record
– Amazon’s AWS cloud business uses Xen
– Verizon launched a new Xen-based cloud
• Linux Foundation Project Partners:
– AMD, Amazon, Cisco, Citrix, Google, Intel,
NetApp, Oracle, Samsung, Verizon, and more

11. Xen: Secure
• SELINUX
• FLASK
– SELINUX capabilities at the VM level by the same team
• Disaggregation
– Segment device drivers into discrete VMs
• Architectural advantages of a Type-1 Hypervisor
– See my separate talk on security from CloudOpen NA 2013

12. Xen: Configurable at Scale
• Toolstacks give rich API and command line capabilities
• Not GUI-centric
• Empowers orchestration via scripting, power tools (Puppet,
Chef, etc.), GUIs, and Cloud layers

13. Xen: Rich Toolstacks
Hypervisor
Toolstack / Console
Xen Hypervisor
Default / XL (XM)
Libvirt / VIRSH
XAPI / XE
Increased level of functionality and integration with other components
Single Host
Basic Functions
Single Host
Additional Functionality
Multiple Hosts
Additional Functionality

14. Xen: Tools for Different Solutions
Project
Toolstack / Console
Xen Hypervisor
Default / XL (XM)
Libvirt / VIRSH
XAPI / XE
Increased level of functionality and integration with other components
Products
Oracle VM
Huawei UVP
Citrix XenServer
14

15. Xen: Tools for Different Clouds
Project
Toolstack / Console
Xen Hypervisor
Default / XL (XM)
Libvirt / VIRSH
XAPI / XE
Increased level of functionality and integration with other components
Products
Oracle VM
Huawei UVP
Citrix XenServer
Used by …
15

16. Focus on XAPI: The Cloud Layer
Xen Hypervisor
XAPI / XE
• 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
Multiple Hosts
Additional Functionality
• 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.xenproject.org/wiki/XCP_Release_Features

17. Xen: A Multi-tenant Solution
• Multiple groups share common resources securely
– Clouds require sharing common resources
– Organizations often need their VMs to be visible to each other,
but entirely invisible to all other VMs
– XAPI makes this happen
– Critical ability for hosting providers

18. Xen: Doesn’t lock you in
• Xen does not force its view of the Cloud on you
• Xen does not force you to use a “favored” Cloud solution
• This is one of the reasons why Cloud innovation happens in
the world of FOSS: It gives power to the Cloud, but allows
Cloud orchestration solutions to innovate
• There is no attempt to bend your efforts to the will of
some corporate business plan

19. XAPI : Orchestration Choices
Xen Hypervisor
XAPI / XE
Multiple Hosts
Additional Functionality

20. Xen Project Healthcheck

21. News: Xen Project in Linux Foundation
• See the following teams on the new XenProject.org site:
–
–
–
–
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

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

23. More Xen Features
• Live Migration of VMs: XenMotion (via XAPI)
• High Availability: Remus
• Wide variety of Control Domains supported
• Even wider variety of Guest Domains
• Multiple virtualization modes improve performance

24. Hypervisor Architecture

25. 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
Device Drivers/Models
I/O
Memory
Hypervisor
MMU
CPUs
Host HW
Provides partition isolation + reliability,
higher security

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

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

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

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

30. Xen Project and Linux
• Xen Hypervisor is not in the Linux kernel
• BUT: everything Xen and Xen Guests need to run is
• Xen packages in all distros (not RHEL6, but CentOS 6)
–
–
–
–
Install Control Domain (Dom0) Linux distribution
Install Xen package(s) or meta package
Reboot
Configure stuff: set up disks, peripherals, etc.
More info: wiki.xenproject.org/wiki/Category:Host_Install

31. Basic Xen Concepts
Console
•
Interface to the outside world
Control Domain aka Dom0
VMn
Control domain
(dom0)
VM1
VM0
Guest OS
and Apps
Dom0 Kernel
Scheduler
MMU
XSM
Hypervisor
•
•
Guest Domains
•
Memory
Trusted Computing Base
CPUs
Your apps
Driver/Stub/Service Domain(s)
•
I/O
Dom0 kernel with drivers
Xen Management Toolstack
Host HW
•
•
A “driver, device model or control
service in a box”
De-privileged and isolated
Lifetime: start, stop, kill
31

32. Basic Xen Concepts: Toolstack+
Console
Console
•
Interface to the outside world
Control Domain aka Dom0
VMn
Control domain
(dom0)
VM1
VM0
Toolstack
Guest OS
and Apps
Dom0 Kernel
Scheduler
MMU
XSM
Hypervisor
•
•
Guest Domains
•
Memory
Trusted Computing Base
CPUs
Your apps
Driver/Stub/Service Domain(s)
•
I/O
Dom0 kernel with drivers
Xen Management Toolstack
Host HW
•
•
A “driver, device model or control
service in a box”
De-privileged and isolated
Lifetime: start, stop, kill
32

33. Basic Xen Concepts: Disaggregation
Console
Console
•
Interface to the outside world
Control Domain aka Dom0
VMn
Control domain
(dom0)
Toolstack
VM1
One or more
driver, stub or
service domains
Dom0 Kernel
Scheduler
MMU
XSM
VM0
Guest OS
and Apps
Hypervisor
•
•
Guest Domains
•
Memory
Trusted Computing Base
CPUs
Your apps
Driver/Stub/Service Domain(s)
•
I/O
Dom0 kernel with drivers
Xen Management Toolstack
Host HW
•
•
A “driver, device model or control
service in a box”
De-privileged and isolated
Lifetime: start, stop, kill
33

34. Xen : Types of Virtualization

35. Xen Virtualization Vocabulary
• PV – Paravirtualization
– Hypervisor provides API used by the OS of the Guest VM
– Guest OS needs to be modified to provide the API
• HVM – Hardware-assisted Virtual Machine
– Uses CPU VM extensions to handle Guest requests
– No modification to Guest OS
– But CPU must provide VM extensions
• FV – Full Virtualization (another name for HVM)

36. Xen Virtualization Vocabulary
• PVHVM – PV on HVM drivers
– Allows H/W virtualized guests to use PV disk and I/O drivers
– No modifications to guest OS
– Better performance than straight HVM
• PVH – PV in HVM Container (coming in 4.4)
– Almost fully PV
– Uses HW extensions to eliminate PV MMU
– Possibly best mode for CPUs with virtual H/W extensions

37. 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
PVHVM
P
P
VS
VH
P
P
P
VH
P
P
P
P
PVH
Fully Paravirtualized (PV)
Xen 4.4
HVM mode/domain
PV mode/domain

38. 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
PVHVM
P
P
VS
VH
P
P
P
VH
P
P
P
P
PVH
Fully Paravirtualized (PV)
Xen 4.4
HVM mode/domain
PV mode/domain

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

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

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

42. Next: XAPI Architecture Diagram
Before and After Disaggregation

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

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

45. 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 (Linux Security Modules)
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
45

46. Xen Security Modules (XSM) -- FLASK
• What does FLASK provide?
– Granular security
•
•
•
•
•
•
•
Can a guest domain talk with other guest domains?
Can a guest domain only communicate with the Control Domain?
Can a Guest domain have memory which cannot be read by the Control Domain?
What type of device model is used in this domain?
The ability to define multiple security roles on the domain level
User types can be defined and assign roles
Policy constraint logic
More info: http://wiki.xenproject.org/wiki/Xen_Security_Modules_:_XSM-FLASK
46

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

48. ARM Hypervisor

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

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

51. Xen + ARM = a perfect Match
ARM Architecture Features for Virtualization
ARM SOC
EL0
Device Tree describes …
EL1
I/O
HVC
GT
GIC
v2
2 stage
MMU
EL2
Xen Hypervisor

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

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

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

55. Code Size of x86 and ARM Hypervisors
X86 Hypervisor
100K -120K LOC
Any x86 CPU
ARM Hypervisor for
mobile Devices
60K LOC
ARM Hypervisor for
Servers
17K LOC
ARM v5 – v7
(no virtual extensions)
(extra code for RT)
ARM v7+
(w/ virtual extensions)

56. Mirage OS

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

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

59. What’s Next?

60. New in Xen 4.3 (July 2013)
•
•
•
•
•
Xen ARM for Servers
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, …
Next Release Info: http://wiki.xenproject.org/wiki/Xen_Roadmap/4.4

61. What’s next (and already happening)
• Establish a shared test infrastructure
– Most major contributors are duplicating effort
– Mirage OS provides interesting opportunities
• Usability and better distribution integration
– Example: Xen + XAPI in CentOS 6.4
• More focus on downstreams
– Examples: CloudStack and Xen Orchestra
• Disaggregation in Xen toolstacks (e.g XAPI)
• Better Libvirt and virt-manager integration
– Embed Xen more into the Linux ecosystem and provide benefits for the
wider Linux community

62. Getting Started with Xen Project
•
•
•
•
Document Days (monthly)
Test Days (prior to release)
Mailing Lists , IRC, Newsletter
XenProject.org (sign up, it’s free!)
Xen Hackathon, Next one expected Spring 2014
Xen Developer Summit, 10/25-26, Edinburgh
Xen User Summit, last month, New Orleans

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