Xen 4.2 Release Notes

This is a draft of the Xen 4.2 release notes. Xen 4.2 is not yet released.

New Features

High level features include:

• 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 256 Host CPUs for 64 bit HV
  • Multiple PCI segment support
  • Prefer oxenstored when present
• Performance
  • PCI pass-through for Linux Guests (see "Xen 4.2: XL and PCI pass-through")
  • 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 support
• Libvchan cross domain comms in Xen mainline
• XL improvements, XEND is formally deprecated. For a feature comparisan see "XL vs Xend Feature Comparison".
• Documentation improvements (e.g. "man pages")
• RAS:
  • Enhanced MCA support to include more failure types
  • APEI support (ACPI Platform Error Interface)

A more complete list of new features and changes is available at Xen 4.2

Default Toolstack

XL is now the default toolstack supplied with Xen. Please see the XL page for guidance on migrating from Xend.

The previous Xend toolstack is now formally deprecated and should be expected to be removed in the 4.3 timescale. Therefore it is strongly recommended that users evaluate Xen 4.2 with XL for their use case and report any omissions or blockers such that they can be addressed for 4.3.

Build Requirements

The requirements for building Xen are documented in the README file in the Xen source tree.

Some additional build dependencies have been added since Xen 4.1:

• libyajl
• glib
• pkg-config
• markdown (optional)

In addition Xen will now prefer to use the system wide libaio if it is available. If libaio is not installed then an intree version will be used. Users are strongly encouraged to install their distribution's version of libaio.

An additional step has also been added to the build process. It is now necessary to run:

$ ./configure

before building the tools (e.g. make tools, make world, make dist etc).

As a consequence of this change Xen now defaults to installing libraries into /usr/lib by default. Users on systems which use /usr/lib64 for 64-bit libraries should use the --libdir option. e.g:

$ ./configure --libdir=/usr/lib64