Xen Project 4.21 Release Notes

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Revision as of 08:44, 19 November 2025 by Olkur (talk | contribs) (Created page with "= Overview = Xen Project 4.21.0 was released on 19th of November 2025. Xen Project 4.21.0 is the work of 8 months of development. = New Feature Highlights = The list of new features can be found on the following page: Xen Project 4.21 Feature List You can find information on support status (including security support) for various features in [https://xenbits.xenproject.org/docs/4.21-testing/SUPPORT.html SUPPORT.md] and [https://xenbits.xen.org/docs/unstable/supp...")
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Overview

Xen Project 4.21.0 was released on 19th of November 2025.

Xen Project 4.21.0 is the work of 8 months of development.

New Feature Highlights

The list of new features can be found on the following page: Xen Project 4.21 Feature List

You can find information on support status (including security support) for various features in SUPPORT.md and Hypervisor Support Matrix.

Documentation is available online: Xen 4.21 Documentation

Build Requirements

Xen requires gcc v5.1 or later (x86), gcc 5.1 or later (arm32), or gcc 5.1 or later (arm64), gcc 12.2 or later (riscv64).

Build

First of all you will have to get the Xen 4.21 source code, which you can either download through our release tarball (including signature) from our download page. Alternatively, you can get the source in the following way:

  • With a recent enough git (>= 1.7.8.2) just clone and checkout the proper tag (RELEASE-4.21.0) from the xen.git repo directly:
git clone -b RELEASE-4.21.0 https://xenbits.xenproject.org/git-http/xen.git

Build instructions can be found at Compiling Xen From Source or Compiling Xen From Source on NetBSD.

Changes affecting downstreams and users

  • The minimum toolchain requirements have increased for some architectures
  • New dependency on library json-c 0.15 or later, the toolstack will prefer it
 to `YAJL` when available.
  • Introduce libxenmanage as a stable library, replacing xenstored's
 dependency on unstable libraries.
  • Allow configuring the number of altp2m tables per domain via vm.cfg.
  • Introduce new PDX compression algorithm to cope with Intel Sierra Forest and
 Granite Rapids having sparse memory maps.
  • New amd-cppc/amd-cppc-epp cpufreq driver.
  • GNTTABOP_cache_flush: it's unused on x86 and the implementation is
 broken.
  • Support of qemu-traditional has been removed.
  • The in-tree oxenstored is deprecated and will be removed in a future
 version of Xen.  It is moving into the Xapi project
 https://github.com/xapi-project/oxenstored so it can be maintained in line
 with the other Ocaml projects in the Xen ecosystem.

Known issues

While we do the utmost to make the release perfect, there are always fixes which are not quite complete on time. We will add those here. So if you run into trouble, please check this section.

Currently known issues are: