Xen 4.2 Feature List

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Revision as of 12:14, 7 September 2012 by Ijc (talk | contribs) (Sync with release notes)
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 usermode of 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
    • Multiple PCI segment support
    • Prefer oxenstored when present
  • Performance
    • PCI pass-through for Linux Guests
    • AMD SVM DecodeAssist support
    • Remus memory image compression
    • Scheduler improvements (sched_ratelimit_us and tslice_ms; see "new commands" and "Xen 4.2: CPUPOOLS")
  • EFI boot support for the 64 bit hypervisor hosts
  • 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


  • Documentation improvements (e.g. man pages)
  • Lots of bug fixing of course.


  • XL is now default toolstack and XEND is formally deprecated
  • libxl improvements
    • The libxl API is now stable.
    • The libxl featureset has been greatly expanded:
      • Many slow 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; nearing feature parity (non default still, but we want people to be testing it)
  • Added libvchan to xen mainline(cross domain comms)


  • Improvements to paging and sharing, enabling higher VM density for VDI use-cases
  • EFI (extensible Firmware Interface) support for HV (i.e. if I have a machine that has EFI, I can use Xen on it)
  • Support up to 256 Host CPUs for 64 bit h/v (from 128)
  • Support dom0 kernels compressed with xz
  • Per-device interrupt remapping (increases scalability)
  • Support for pvhvm guest direct pirq injection (Performance improvement for PCI passthrough for Linux Guests)
  • Intel SMEP (Supervisor Mode Execution Protection) support
  • Mem event stuff? (Allows to externally observe what guests are up to and can be used for external virus checking - not sure what the right terminology is)
  • Multiple PCI segment support
  • Added xsave support(floating point)
  • 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)
  • New scheduler parameters [1]

Removed Functionality

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

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