Xen 4.2 Feature List

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

General

• Documentation improvements. Documentation is now available online:
  • man pages
  • hypervisor command line options
  • full listing:
• Lots of bug fixing of course.

Tools

• 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.

Xen

• 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