Difference between revisions of "Xen 4.2 Feature List"

From Xen
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** Enhanced MCA support to include more failure types
** Enhanced MCA support to include more failure types
** APEI support (ACPI Platform Error Interface)
** APEI support (ACPI Platform Error Interface)
* Credit Scheduler [[Credit_Scheduler#Xen4.2|tuning parameters]:
* Credit Scheduler [[Credit_Scheduler#Xen4.2|tuning parameters]]:
** '''sched_ratelimit_us'''
** sched_ratelimit_us
** '''tslice_ms'''
** tslice_ms
* [[Xen_4.2:_cpupools|cpupools]]
* [[Xen_4.2:_cpupools|cpupools]]

Revision as of 13:01, 7 September 2012

Icon Info.png This is a preliminary list of Xen 4.2 features

Other Xen Releases

See Xen Release Features for a comparison of the featureset of different Xen releases.

High Level features

  • Security:
    • Support for Intel Supervisor Mode Execution Protection (SEMP), which prevents the execution of usermode pages by the Xen hypervisor, making many application-to-hypervisor exploits much harder.
    • Various Xen Security Modules (XSM) / Flask improvements. The XSM framework and the Xen Flask security module is an application of the Flask architecture to the Xen hypervisor.
  • Scalability:
    • Increased VM density for VDI use-cases
    • Up to 4095 Host CPUs for 64 bit hypervisor
    • Up to 5TB host memory support for 64 bit hypervisor
    • Up to 512 VCPUs per PV VM and 256 VCPUs per HVM VM
    • Support for multiple PCI segments
    • Prefer oxenstored when present
  • Performance
    • AMD SVM DecodeAssist support
    • Scheduler improvements
  • EFI boot support for hosts using the 64 bit hypervisor
  • XL improvements, XEND is formally deprecated
  • Documentation improvements (e.g. man pages)
  • RAS:
    • Enhanced MCA support to include more failure types
    • APEI support (ACPI Platform Error Interface)

Detailed List



  • XL is now default toolstack and XEND is formally deprecated
    • For a feature comparison between XL and XEND see "XL vs Xend Feature Comparison".
    • lots of XL improvements, e.g.
      • More complete support for toolstack operations. Includes all basic and day to day functionality and many advanced features.
      • Support for Network driver domains in XL
      • Improved support for PCI pass-through (see "Xen 4.2: XL and PCI pass-through")
  • libxl improvements
    • The libxl API is now stable.
    • The libxl featureset has been greatly expanded:
      • Long running operations can now be done asynchronously.
      • Improved event handling subsystem.
  • Remus compression (compression of memory image improves performance)
  • Prefer oxenstored when available. Oxenstored is faster, more scalable and more reliable than the C xenstored. In particular the transaction model in oxenstored does not involve taking a complete copy of the database and aborting on any (even non-conflicting) other change. For more detail on the design, implementation and a performance comparison see this paper.
  • Support for upstream qemu
    • Used by default when required for PV guests (e.g. qdisk backend or VFB support)
    • Optional for use with HVM guests.
  • Added libvchan interdomain communication library.


  • Improvements to paging and sharing, enabling higher VM density for VDI use-cases
  • EFI (extensible Firmware Interface) support for hypervisor. Allows Xen to boot on machines which use EFI rather than a traditional BIOS
  • Support up to 4095 Host CPUs for 64 bit h/v (from 256)
  • Support for dom0 kernels compressed with xz
  • Per-device interrupt remapping (increases scalability)
  • Support for PVHVM guest direct physical IRQ injection (improves performance for PCI passthrough to Linux Guests)
  • Intel SMEP (Supervisor Mode Execution Protection) support
  • Multiple PCI segment support
  • Added xsave support (support for newer floating point hardware features)
  • Lots of XSM / Flask fixes (security)
  • AMD SVM "DecodeAssist" support (AMD CPU feature that avoids emulation and increases performance)
  • RAS:
    • Enhanced MCA support to include more failure types
    • APEI support (ACPI Platform Error Interface)
  • Credit Scheduler tuning parameters:
    • sched_ratelimit_us
    • tslice_ms
  • cpupools

Removed Functionality

  • ACM (alternative XSM to Flask) was removed (unmaintained)
  • Removed vnet (unmaintained)
  • The IA64 port was removed (unmaintained)

Deprecated Functionality

  • The XEND toolstack is now deprecated.

Xen Development Support

  • Can build with clang
  • Added "make deb" target
  • Lots of xentrace improvements
  • update ocaml bindings and make them usable by xapi (which previously had it's own fork of the same codebase)

Also See

  • Category:Xen 4.2 - Contains articles and tutorials related to new functionality in Xen 4.2