Xen Project Delivers Xen 4.21, a Modernized Hypervisor with Broader Architecture Support and Improved Performance

Xen 4.21 takes a major step towards modernized virtualization, offering greater maintainability across industries and upgraded efficiency for memory

SAN FRANCISCO, Nov. 19, 2025 /PRNewswire/ -- The Xen Project, an open source hypervisor hosted at the Linux Foundation, today announced the release of Xen 4.21, which updates toolchain requirements across all architectures, improves runtime performance on x86 with smarter memory and cache handling, delivers enhanced security on Arm®-based devices, and adds early RISC-V enablement. This release marks another major modernization milestone for the Xen hypervisor, preparing the Xen Project to support automotive and embedded systems of the future.

For data center and cloud environments, Xen 4.21 delivers more efficient virtualization through smarter cache management, improved PCI handling, and a new AMD CPPC driver that provides finer-grained CPU frequency control. These updates translate to better performance per watt and improved scalability across modern multi-core servers, helping operators run more VMs with less overhead.

In the automotive and embedded space, Xen's progress toward functional-safety compliance and dom0less virtualization enables reliable, secure isolation for instrument clusters, infotainment, and driver-assistance systems. Demonstrations from AMD and Honda at Xen Summit 2025 showcased these capabilities running on real hardware, reinforcing Xen's growing role in production-ready automotive platforms.

Together, these advancements highlight Xen's versatility as a single hypervisor platform that scales from high-performance data centers to safety-critical embedded systems. Work on MISRA-C compliance, dom0less virtualization, and Arm Memory Protection Unit (MPU) support demonstrates Xen's ongoing progress toward functional-safety standards, strengthening its position as a modern, open foundation for the future of virtualization.

"Xen 4.21 shows that open source virtualization is anything but standing still," said Cody Zuschlag, Community Manager for the Xen Project. "We're modernizing the hypervisor from the inside out: updating toolchains, expanding architecture support, and delivering the performance that next-generation hardware deserves. It's exciting to see Xen powering everything from next generation cloud servers to real-world automotive systems."

Xen 4.21 addresses the needs of modern architecture with several integral upgrades, including:

• Modernized foundations and toolchain updates: Xen 4.21 raises the minimum supported versions of GCC, Binutils, and Clang across all architectures, reducing technical debt and improving long-term maintainability. Additionally, Xen 4.21 now formally supports and maintains the use of qemu-xen device models inside a Linux stubdomain, strengthening the security posture of existing downstream projects such as QubesOS.
• Improved x86 performance and hardware flexibility: Included in version 4.21 is a new PDX compression algorithm to reduce hypervisor memory footprint, amd-cppc and amd-cppc-epp cpufreq drivers to enable fine-grained CPU performance scaling on AMD processors through Collaborative Processor Performance Control (CPPC), and resizable BARs now supported for PVH dom0 to allow devices to expose larger memory regions and improving I/O efficiency.
• Expanded support for Arm-based automotive and edge platforms with enhanced security: Xen 4.21 introduces new advancements for automotive and edge applications that require the highest levels of safety, reliability, and performance. This release adds stack protector enablement for improved hypervisor robustness and introduces support for the Extended Shared Peripheral Interrupt (eSPI) range on SoCs with GICv3.1+, improving compatibility with newer automotive and embedded systems. MISRA-C fixes and compliance work continue to raise code quality. Support for split hardware and control domains, dom0less virtualization refactoring, and finer-grained Kconfig options help create smaller and more safety-certifiable builds. Xen 4.21 also adds progress toward MPU support for Arm Cortex®-R52 and Arm Cortex-R82 processors and virtio-pci with parallel boot for dom0less systems. Together, with the existing support for Arm Cortex-A CPUs, these updates move Xen closer to full functional-safety readiness.
• Continued expansion into new architectures: RISC-V support progresses with the addition of UART and external interrupt handling in hypervisor mode. These changes establish the groundwork for future RISC-V guest virtualization and hardware enablement.

The Xen Project is supported by industry members including AMD, Arm, AWS, EPAM, Ford, Honda, Renesas, Vates, and XenServer, along with a global community of maintainers and contributors collaborating under the Linux Foundation.

To follow the Xen Project's development, and download Xen 4.21, visit https://xenproject.org/resources/downloads/.

Supporting Quotes

"This release shows how far the Xen community has come, and how aligned we are on building a hypervisor that's both modern and resilient. The improvements led by safety-critical use cases raise the bar for everyone, including cloud and enterprise environments. At Vates, we're fully committed to this shared vision of open, sustainable virtualization."
– Olivier Lambert, CEO, Vates

"The Xen 4.21 release is another testament to the power of open-source innovation, bringing critical performance and stability improvements to modern cloud and data center workloads. Specifically, updates like the newly introduced page index compression algorithm and better memory cache attribute management translate into better performance, improved scalability for all our enterprise XenServer users. Citrix remains deeply committed to the Xen hypervisor community, ensuring these advancements translate into superior security and reliability for our enterprise XenServer users."
– Jose Augustin, Product Management, Citrix | XenServer

"Virtualization is becoming central to how automotive and edge systems deliver safety, performance, and flexibility, reflecting a broader shift toward software-defined architectures that enable continuous innovation. By expanding support for Arm Cortex-R technology, the latest Xen 4.21 release will help advance more scalable, secure, and safety-critical deployments on Arm-based platforms."
– Andrew Wafaa, Senior Director, Software Communities, Arm

"Xen 4.21 enhances automotive virtualization with architecture-independent parallel VM boot and continued MISRA-C compliance efforts. The new release simplifies configuration and validation of Xen-based PoCs for critical workloads such as infotainment and instrument cluster systems."
– Denis Mukhin, Staff Embedded Software Engineer, Ford Motor Company

"The 4.21 release of Xen is a significant milestone for the community, delivering multiple enhancements for Automotive industry adoption. With changes ranging from functional safety compliance improvements to power management and PCI support on Arm, Xen has become a true enabler of mixed-criticality support for in-vehicle High-Performance Compute. We at EPAM believe this release will serve as a solid foundation for kicking off automotive product integration based on the Xen Project."
– Artem Mygaiev, Technology Solutions Director, EPAM

About the Xen Project
Xen Project software is an open source virtualization platform licensed under the GPLv2 with a similar governance structure to the Linux kernel. A project at The Linux Foundation, the Xen Project community is focused on advancing virtualization in a number of different commercial and open source applications including server virtualization, Infrastructure as a Services (IaaS), desktop virtualization, security applications, embedded and hardware appliances. It counts many industries and open source community leaders among its members including AMD, Arm, AWS, Epam, Ford Motor Company, Honda, Renesas, Vates, and XenServer (Citrix). For more information about the Xen Project software and to participate, please visit XenProject.org.

About the Linux Foundation 
The Linux Foundation is the world's leading home for collaboration on open source software, hardware, standards, and data. Linux Foundation projects are critical to the world's infrastructure, including Linux, Kubernetes, LF Decentralized Trust, Node.js, ONAP, OpenChain, OpenSSF, PyTorch, RISC-V, SPDX, Zephyr, and more. The Linux Foundation focuses on leveraging best practices and addressing the needs of contributors, users, and solution providers to create sustainable models for open collaboration. For more information, please visit us at linuxfoundation.org.

The Linux Foundation has registered trademarks and uses trademarks. For a list of trademarks of The Linux Foundation, please see its trademark usage page: www.linuxfoundation.org/trademark-usage. Linux is a registered trademark of Linus Torvalds.

Media Contact
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The Linux Foundation
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SOURCE Xen Project