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Software-update: Xen 4.10.0

Xen is een baremetal-hypervisor voor het x86- en ARMv7/v8-platform, en laat diverse besturingssystemen gelijktijdig op één systeem draaien zonder de prestaties drastisch te beïnvloeden. Voor meer informatie over Xen en de bijbehorende community verwijzen we naar deze en deze pagina. Op dit moment worden alleen Linux, NetBSD en FreeBSD als hostsystemen ondersteund, maar men is druk bezig om ook andere besturingssystemen volledig te ondersteunen. De ontwikkelaars hebben versie 4.10.0 uitgebracht met de volgende aankondiging:

What’s New in the Xen Project Hypervisor 4.10

I am pleased to announce the release of the Xen Project Hypervisor 4.10. As always, we focused on improving code quality, security hardening as well as enabling new features.

The Xen Project Hypervisor 4.10 continues to take a security-first approach with improved architecture and more centralized documentation. The release is equipped with the latest hardware updates from Arm and a more intuitive user interface.

We are also pleased to announce that Jürgen Groß will be the next release manager for Xen Project Hypervisor 4.11. Jürgen has been an active developer for the past few years, making significant code contributions to advance Xen support in Linux. He is a virtualization kernel developer at Suse and maintainer of Xen subsystem in Linux as well as parvirtualization.

Hypervisor General

Credit 2 scheduler improvements: Soft-affinity support for the Credit 2 scheduler was added to allow those using the Xen Project in the cloud and server space to specify a preference for running a VM on a specific CPU. This enables NUMA aware scheduling for the Credit 2 scheduler. In addition we added cap support allowing users to set a the maximum amount of CPU a VM will be able to consume, even if the host system has idle CPU cycles.

Null scheduler improvements: The recent updates to the “null” scheduler guarantee near zero scheduling overhead, significantly lower latency, and more predictable performance. Added tracing support enables users to optimise workloads and introduced soft-affinity. Soft affinity adds a flexible way to express placement preference of vcpus on processors, which improves cache and memory performance when configured appropriately.

Virtual Machine Introspection improvements: Performance improvements have been made to VMI. A software page table walker was added to VMI on ARM, which lays the groundwork to alt2pm for ARM CPUs. For more information on alt2pm is available here.

PV Calls Drivers in Linux: In Xen Project 4.9, the Xen Project introduced the PV Calls ABI, which allows forwarding POSIX requests across guests. This enables a new networking model that is a natural fit for cloud-native apps. The PV Calls backend driver was added to Linux 4.14.

Better User Experience through the Xen Project User Interface
The Xen Project community also made significant changes to the hypervisor’s user interface. It is now possible to modify certain boot parameters without the need to reboot Xen. Guest types are now selected using the type option in the configuration file, where users can select a PV, PVH or HVM guest. The builder option is being depreciated in favor of the type option, the PVH option has been removed and a set of PVH specific options have been added.

These changes allow the Xen Project to retain backward compatibility on new hardware without old PV code, providing the same functionality with a much smaller codebase. Additional user interface improvements are detailed in our blog post.

Hypervisor Arm

Support for Latest System-on-chip (SoC) Technology: The Xen Project now supports SoCs based on the 64-bit Armv8-A architecture from Qualcomm Centriq 2400 and Cavium ThunderX.

SBSA UART Emulation for Arm® CPUs: Implementation of SBSA UART emulation support in the in the Xen Project Hypervisor makes it accessible through the command line tools. This enables the guest OS to access the console when no PV console driver is present. In addition, the SBSA UART emulation is also required to be compliant with the VM System specification.

ITS support for ARM CPUs: Xen Project 4.10 adds support for ARM’s Interrupt Translation Service (ITS), which accompanies the GICv3 interrupt controller such as the ARM CoreLink GIC-500. ITS support allows the Xen Project Hypervisor to harnesses all of the benefits of the GICv3 architecture, improving interrupt efficiency and allowing for greater virtualization on-chip for both those using the Xen Project for the server and embedded space. ITS support is essential to virtualize systems with large amounts of interrupts. In addition ITS increases isolation of virtual machines by providing interrupt remapping, enabling safe PCI passthrough on ARM.

GRUB2 on 64-bit Armv8-A architecture: The GRUB community merged support to boot Xen on 64-bit Arm-based CPU platforms. GRUB2 support for Armv8-A improves the user experience when installing Xen via distribution package on UEFI platform.

Hypervisor x86

Rearchitecture Creates Smaller Attack Surface and Cleaner Code
Since the introduction of Xen Project Hypervisor 4.8, the project has overhauled the x86 core of its technology. The intention is to create a cleaner architecture, less code and a smaller computing base for security and performance. As part of this re-architecture, Xen Project 4.10 supports PVHv2 DomU. PVHv2 guests have a smaller TCB and attack surface compared to PV and HVM guests.

In Xen Project Hypervisor 4.9, the interface between Xen Project software and QEMU was completely reworked and consolidated via DMOP. For the Xen Project Hypervisor 4.10, the Xen Project community built on DMOP and added a Technology Preview for dm_restrict to constrain what device models, such as QEMU, can do after startup. This feature limits the impact of security vulnerabilities in QEMU. Any previous QEMU vulnerabilities that could normally be used for escalation privileges to the host cannot escape the sandbox.

This work significantly reduces potential security vulnerabilities in the Xen Project software stack.

L2 CAT for Intel CPUs: In Xen 4.10 we added support for Intel’s L2 Cache Allocation Technology(CAT) — available on certain models of (Micro) Server platforms. Xen L2 CAT support provides Xen users a mechanism to partition or share the L2 Cache among virtual machines, if such technology is present on the hardware Xen runs. This allows users to make better use of the shared L2 cache depending on the VM characteristic (e.g. priority).

Local Machine-Check Exception(LMCE) for Intel CPUs: Xen 4.10 provides LMCE support for HVM guests. A LMCE, if the affected vCPU is known, will be injected to related vCPU, otherwise, the LMCE will be broadcasted to all vCPUs running on the host. This allows for more efficient passing of MCE from hypervisor to virtual machines for further handling.

User Mode Instruction Prevention(UMIP) for Intel CPUs: User-Mode Instruction Prevention (UMIP) is a security feature present in new Intel Processors. If enabled, it prevents the execution of certain instructions if the Current Privilege Level (CPL) is greater than 0. Xen 4.10 exposes UMIP to virtual machines to take advantage of this feature.


Improved Support Documentation
In Xen Project 4.10, a machine-readable file ( was added to describe support related information in a single document. It defines support status and whether features are security supported and to which degree. For example, a feature may be security supported on x86, but not on Arm.

This file will be back-ported to older Xen releases and will be used to generate support information for Xen Project releases and will be published on This effort will both allow users to better understand how they are impacted by security issues, and centralizing security support related information is a pre-condition to become a CVE Numbering authority.


Despite the shorter release cycle, the community developed several major features, and found and fixed many more bugs. It is also rather impressive to see multiple vendors collaborate on the Xen Project Hypervisor to drive multiple projects forward. Contributions for this release of the Xen Project came from Amazon Web Services, AMD, Aporeto, Arm, BAE Systems, BitDefender, Cavium, Citrix, EPAM, GlobalLogic, Greenhost, Huawei Technologies, Intel, Invisible Things Lab, Linaro, Nokia, Oracle, Red Hat, Suse, US National Security Agency, and a number of universities and individuals.

As in Xen 4.9, we took a security-first approach for Xen 4.10 and spent a lot of energy to improve code quality and harden security. This inevitably slowed down the acceptance of new features somewhat and also delayed the release. However, we believe that we reached a meaningful balance between mature security practices and innovation.

On behalf of the Xen Project Hypervisor team, I would like to thank everyone for their contributions (either in the form of patches, code reviews, bug reports or packaging efforts) to the Xen Project. Please check our acknowledgement page, which recognises all those who helped make this release happen.

The source can be located in the 4.10.0 tree (tag RELEASE-4.10.0) or can be downloaded as tarball from our website. For detailed download and build instructions check out the guide on building Xen 4.10
Versienummer 4.10.0
Releasestatus Final
Besturingssystemen Linux, BSD
Website Xen
Licentietype Voorwaarden (GNU/BSD/etc.)



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Bron: Xen


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Reacties (5)

Wijzig sortering
Artikel: "Op dit moment worden alleen Linux, NetBSD en FreeBSD als hostsystemen ondersteund".
Xen website: "Supports multiple guest operating systems: Linux, Windows, NetBSD, FreeBSD".
M.i. wordt daarmee bedoeld dat Xen alleen op die hostsystemen kan worden ge´nstalleerd, dat je een Windows guest (dus VM) kan draaien is weer een ander verhaal.
Je hebt gelijk. I nam aan dat op een bare-metal hypervisor geen host OS aanwezig zou zijn, maar bij Xen kan dat een range aan Linux distributies zijn, en niet Windows. Bare-metal betekent niet host-loos. Weer wat geleerd.
De term "host" is hier waarschijnlijk wat ongelukkig gekozen. Voor zover ik weet (maar correct me if I'm wrong, ik heb me alweer een tijd niet verdiept in hypervisors) heeft Xen een zogenaamde dom0, wat je management host is. Deze draait op het hypervisor want Xen is bare-metal en draait dus op de hardware, je kunt hem dus ook herstarten en dan draaien de andere VM's gewoon door, maar je hebt hem wel nodig om je virtualisatieomgeving te beheren.

Edit: laatste deel sloeg nergens op, een herstart van dom0 herstart je hele Xen hypervisors en dus ook je andere VM's.

[Reactie gewijzigd door rbr320 op 19 december 2017 17:23]

Ooit heb ik bij VMware op training nog duidelijk uitleg gekregen over het verschil tussen 'host' en 'guest': Host is de gastheer (gastvrouw?) dus het OS dat op de fysieke machine is ge´nstalleerd.
Guest is de gast die gebruik maakt van de services van de host.

Bij VMware is daar bij 'hosted' virtualisatie een duidelijk verschil tussen: De host kan geen gebruik maken van de voordelen van virtueel draaien.

Bij Xen is dat net even iets anders: Daar is de hypervizor (de virtualisatie software) zo in het host-os geweven dat je zou kunnen zeggen dat de host ook deels als gast draait. De netwerk kaart krijgt soms een mac address uit de gasten reeks en is ook van een 'virtueel' type.

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