XEN Open Source Hypervisor Name from neXt gENeration virtualization Asst. Prof. NV MahajanCommunity History 2002 Xen hypervisor development starts 2004 Xen 1.0 and 2.0 released, First Xen developer’s summit 2005 XenSource founded, Xen 3.0 released 2006 CPU enhancements for virtualization; Linux distros ship Xen All x86 OSes “enlightened”, VMware and Microsoft adopt paravirtualization First XenEnterprise release Amazon EC2 Launches 2007 XenSource acquired by Citrix Systems, Inc. 2008 Xen embedded in Flash on HP/Dell servers First embedded Xen on laptopsXen Project Mission Build the industry standard open source hypervisor — Core "engine" that is incorporated into multiple vendors! products Maintain Xen’s industry-leading performance — Be first to exploit new hardware acceleration features Help 0S vendors paravirtualize their OSes Maintain Xen’s reputation for stability and quality Security must now be paramount Support multiple CPU types; big and small systems ~ From server to cient to mobile phone Foster innovation Drive interoperability Initially created by University of Cambridge LaboratoryXen Project Advisory Board © Represents major contributors and vendors that offer Xen based products. Current members: w> chex © fg @Bredna Sun Novell. ORACLE! * Defines and approves the Xen® Trademark Policy (“What is Xen?”) * Oversees community code practices and roadmapXen Hypervisor * Is the basic abstraction layer of software that sits directly on hardware below any operating systems * It is responsible for — Scheduling, memory management, interrupt and device control — per-domain and per-vcpu info management * It has no knowledge of networking, external storage devices, video, or any other common I/O functions found on a computing systemXen 3.0 CPU Virtualization * Guest OSs directly call Xen hypervisor instead of emulating sensitive, unprivileged instructions * Xen Hypervisor Platform is comprised of two components — Xen hypervisor which is responsible for the core hypervisor activities such as CPU, memory virtualization, power management — Scheduling of virtual machines * In xen/include/public/xen.h: ~40 hypercalls. E.g. set trap table, mmu update, etc * a fast, very lightweight hypervisor in under 70,000 lines of codeXen Hypervisors : Virtualization Management S/W s . Para-vistualized Para-virtualized — Hardware Virtual Type 1 Hypervisor with PV Spoon ® Tesi ‘Machine (HVM) Most privileged Domain domain(Dom0)> Xen Host Domain U : Xen Guest Virtual 1/0 devices, vAPIC,vPIT,vPIC vMMU,VCPUsXen Hypervisors : Virtualization Management S/W domain(Dom0)> > VM: eave ao Machine gIVN) * isa modified Linux kernel ae * has special rights to access physical I/O resources as well as interact with other virtual machines Domain U :All para-virtualized VM, are modified Linux operating systems. HVM Guests and run standard Windows or any other OS ‘Hardware Platform configured processor with Intel VT-cnablePV Xen Architecture * Xen Hypervisor only handles a few of the instructions, the rest is directly executed by the hardware on behalf of the systemsXen Hypervisor Architecture pv HvM PvHVM Foner Legacy Frontend, Pv Device PV Drivers Drivers Drivers 7 T T ® Memory cpu Timer Xen Hypervisor Management Virtualization VirtualizationXEN Architecture ‘ira Machina Hoa Saver tol Moerine ‘Veua Machioe Vet aehineDomainO(dom0) _ Is a virtual machine, which by default — has direct access to hardware Dom0 provides hardware drivers, communication with hypervisor and the execution of other domains (DomU) Dom0 domain is typically a modified version of Linux, NetBSD or Solaris All Xen virtualization environments require Dom 0 to be running before any other virtual machines can be started Dom0 matches the “host” of other virtualization systems, while a domU can be seen as a “guest” Xen hypervisor remains small and maintainable and that it occupies a little memoryRole of Dom 0 Creates and manages guest VMs Interacts with the Xen hypervisor — Xend (Xen daemon) — Xm(Xen Manager) — Xenstore * Database of configuration information * Used by Domain0 to access guest state * Guest domain drivers can write to xenstore — xenconsoled * Abstraction for guest ttys * Supplies device and I/O services — Runs backend drivers ___— Provides guest storageDomO : Privileged Admin * Xm- Xen Management -main Domain 0 interface for managing Xen guest ‘xm x! xenstore domain: ¥ — omains xend ) QEMUs — to create, pause and shutdown - ~ domains Sara - to list current domains, enable or privemd Legacy Backend pin VCPUs and attach or detach are | Divers | Diners virtual block devices Xend- Xen Daemon- a special process that runs as root in DomainO — Xm sends requests to the xend daemon first, which are in turn relayed to the Xen hypervisor via a hypercallDom0 : Privileged Admin xl (libxl) Xenlight library Xen 4.2 release, xend was declared deprecated and x/ became the default toolstack Xenstored Xen uses a xenstore daemon to allow dom0 and guests get access to information about configuration space for itself and the system Qemu and paravirtual driver backend (high performance passthrough ) Native device driverDrivers with DomO * Two drivers are included in Domain 0 to support network and local disk requests from DomU — Network Backend Driver — Block Backend Driver Network Backend Driver communicates directly with the local networking hardware to process all VM requests coming from the DomU guests Block Backend Driver communicates with the local storage disk to read and write data from the drive based upon DomU requests. . domU Unprivileged domain Each virtual machine is a domU containing a modified Linux kernel Lees | Instead of communicating directly with hardware, it interfaces with Xen hypervisor Domain U PV Guest contains two drivers for network and disk access — PV Network Driver — PV Block DriverXen Hypervisors : Virtualization Management S/W Two drivers are included in Domain 0 to support network and local disk requests from Domain U PV Guests * Network Backend Driver * Block Backend Driver. Dom0: provide user interface to hypervisor> xend-> administrative interaction xenstore->backend storage Domain U P" Penn naan! Access with hardware aware Not aware Other VM running aware Not aware Drivers PY Network Driver No, but special daemon known as PV Block Driver Qemu-dm for networking and disk access requests.Dom 0 to DomU Communication A hypercall is a software trap from a dom0 to the hypervisor Event channel exists between Dom0 and DomU Guest to communicate via asynchronous inter-domain interrupts Is the basic primitive provided by Xen for event notifications Return path from the hypervisor to the domain uses event channelsXen-MS Windows as guests * Xen version 3.0 introduced the capability to run Microsoft Windows as a guest OS unmodified if the host machine's processor supports hardware virtualization provided by Intel VT-x or AMD-V * A Domain U HVM Guest does not have the PV drivers located within the virtual machine; instead a special daemon is started for each HVM Guest in Domain 0Xen Split Device Driver * Xen device drivers are divided into four parts: — Real Device Driver — Bottom Half of Split Device Driver (Back End) — Shared Ring Buffer — Upper Half of Split Device Driver (Front End)Back End Drivers * Responsible for multiplexing of device among all the dom Os and provide generic interface t 0 all the device like disk & NIC * Interact to with real device driver to do actual operation on hardware * Notifies availability of data to destination dom o by Xen EventShared I/O Ring Buffer * Ashared memory segment (Ring based Producer- Consumer) used for exporting the data between the split device drivers * Back end driver allocates shared memory pages and stores its grant reference in the Xenstore * All domains refers to Xenstore to get the reference to shared ring bufferFront End Driver * On reception on Xen Event, queries the Xenstore for grant reference * Using this grant reference, it can retrieve the data from shared ring bufferXen PC! Passtnru * New feature designed to improve overall performance and reduce load on the Dom 0 Guest * Allows the Dom U Guest to have direct access to local hardware without using the Dom 0 for hardware access (QEMU Graphics Virtualization PCI Device/Graphics Pass-through] Service Guest viata) ServicoVM Guest HVA]Warm Migration + Using xm migrate command + Process: ~Pauses a guest Transfers guest state across network to @ new Domaind Resumes guest on destination host + Benefits: Guest and processes remains running “Less data transfer than live migration + Limitations: “Fora short time, the guest is not externally accessible “Requires shared storage Network connections to and from guest are interrupted and will probably timeoutLive Migration * Using xm migrate -live command * «Process: Copies a guest's state to a new domaino -Repeatedly copies dirtied memory until transfer is complete (Pre-copy) + -Re-routes network connections + *Benefits: + No down time, process requires a stoppage of around 60-300 ms to perform final synchronization before VM begins executing at its final destination, providing an illusion of seamless migration Network connections to and from guest often remain active and uninterrupted —Server is still onlineXen Migration Setup * By default migration is disabled * To enable the use of migration a few changes must be made to configuration file /etc/xen/xend-config.sxp. * Need to do changes on both xen host machines * Machine must reside on shared storage * Must be on the same layer 2 network * Sufficient resources needed on target machine * DomainOs must be similaria soe rate pany copy fo = 2 5 © c 20 = o = a}Challenges faced by Xen * Needed to implement features, such as scheduler and memory manager from the ground up *Patches required to build the Linux Domain0 for Xen are still not part of the Linux kernel and require vendors to create and maintain a fork of the Linux kernel —lead to an increased burden on distributors of Xen who cannot easily leverage the features of the upstream kernel —Any new feature, bug fix or patch added to the upstream kernel must be back-ported to work with the Xen patch sets © “Invisible Things Lab” exploit in 2008 where a Xen domU was able to compromise the domainO hostCommercial versions of Xen * With proprietary additions —Citrix XenServer -Oracle VM —Sun xVM (discontinued by Oracle) -Virtual Iron (discontinued by Oracle) -Thinsy CorporationXen Community: Information Sources Xen.org Site ~Source Code www.xen.org/download —Blog blog.xen.org —Mailing Lists lists.xensource.com —Projects www.xen.org/community/projects. html —Wiki wiki.xensource.com —Weekly Community Update wiki.xensource.com/xenwiki/XenWeekly ~Case Studies wiki.xensource.com/xenwiki/Xen_Case_Studies *Other Sites —Solution Search Tool xen.cyberneticos.com Social Networking Facebook, XING, Linkedin, Ohloh, Plaxo, Twitter —Marketing Community (Xen Champions) xenchampions.ning.comerrr reaHypervisors : Virtualization Management S/W Moc eee Prey e eO) TAU PCa en a Ve Xcefromxenore | Huawei UVP Citrix XenServer ) (used |] amazon otc ackspacecloud © Webservices" J