Xen Project improves the art of virtual machine maintenance with annual hypervisor release

Version 4.18 brings first ports to RISC-V and PowerPC, support for next-gen datacenter CPUs

The Xen Project has quietly debuted version 4.18 of its eponymous hypervisor – the year's only release of the virtualization tool.

The update appeared on November 17 and The Register understands a formal announcement will follow on Monday, November 20, US time.

This is not a direction-changing release. It merely offers worthy updates such as 20 security fixes.

Ports to the RISC-V and PowerPC architectures have advanced to what the org describes as "Gitlab-CI doing 'Early printk' (i.e., 'Hello world' implementation)."

On Arm, Xen's developers have merged Scalable Vector Extension (SVE) as a tech preview and done likewise for the Arm Firmware Framework for Arm A-profile. The Arm64 memory subsystem has been made more compliant with the Arm architecture.

For x86 machines, Intel users can now see MSR_ARCH_CAPS info in guests, and controllable from the VM's config file. Xen's feature list explains that means "For CPUs from ~2019 onwards, this allows guest kernels to see details about hardware fixes for speculative mitigations."

AMD's fourth-gen Genoa CPUs and Intel's Granite Rapids both get support for their new features.

The Xen Project has in recent years chosen to focus more on embedded applications. This release advances that shift by adopting more rules set by MISRA-C – the effort to create coding guidelines for C and C++ that promote safety, security and reliability in embedded systems.

Xen 4.17 implemented four directives and 24 rules. Version 4.18 supports six directives and 65 rules of MISRA-C.

That effort has been welcomed by stakeholders who, in canned quotes The Register has seen ahead of Xen's official release announcement, praised the combination of more MISRA-C work and the port to RISC-V as making Xen a better option for embedded, industrial, automotive, and other similar applications.

Which is just what the Xen Project wants.

A decade ago, Xen was a server virtualization contender and a favorite of big clouds, including AWS. But in 2017 the Amazonian cloud adopted a homebrew cut of the KVM hypervisor instead, in part to allow its adoption of the "Nitro" SmartNIC that isolates networking and storage scutwork to free servers' resources to run workloads.

Additions to Xen 4.18 that improve x86 capabilities mean Xen is still more than viable for mainstream compute chores and, combined with the tweaks for embedded and/or industrial roles, also give Intel and AMD more ways to address those markets.

All is not sunshine and rainbows, however. The software shipped known issues that mean the hypervisor will crash if live patching is attempted, or when moving a domain from a cpupool with the credit2 scheduler to another cpupool. Known issues are usually ironed out with minor updates that don't take long to arrive. ®

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