The Xen Project has just announced the release of Xen 4.22, a major update to the open-source type-1 hypervisor which includes new x86 capabilities, better power management for ARM guests, stronger Xenstore resource controls, and carries on the project’s initial efforts in the area of RISC-V virtualization.
A notable new feature on x86 systems is support for Flexible Return and Event Delivery, or FRED. This more recent processor mechanism has been developed to simplify and modernize how interrupts, exceptions, and system calls are handled by reducing some of the complexity of the traditional x86 event-delivery model.
Xen 4.22 also includes support for AMD Bus Lock Threshold, which reduces system-wide performance degradation caused by a virtual machine repeatedly executing atomic instructions that lock the processor bus. Plus, through the standard Power State Coordination Interface, users of Arm systems can now suspend and resume a guest.
The x86 improvements also involve the ability to provide CPIO-packaged CPU microcode as a separate Multiboot module. Furthermore, the xenpm utility is given a new get-core-temp command which allows per-core temperature information to be obtained on Intel processors that are supported.
Moreover, this update also takes Xen’s support for the Arm Firmware Framework as specified for Arm A-profiles up to version 1.2. Work on Armv8-R MPU support is still going on, with the aim of serving embedded and safety-critical systems where memory protection and predictable behavior are especially important.
However, the development of RISC-V support is still ongoing and has not yet reached a stage where it can be used for general-purpose guest virtualization.
A major aspect of the release relates to Xenstore, the shared configuration and coordination service used by Xen domains. In version 4.22, per-domain quotas and watch-depth limits have been introduced in order to prevent any individual guest from using an excessive amount of Xenstore resources.
Along with the changes to the hypervisor, Xen 4.22 also enhances the project’s ability to conduct functional safety testing. It now includes QEMU-based Software-in-the-Loop equipment, which allows for repeatable fault injection and the simulation of interface behavior, and code-coverage tools are available to evaluate the testing starting from basic coverage and extending to modified condition/decision coverage.
Finally, according to the devs, the project has likewise continued to remove interfaces that have long since become obsolete, as well as other obsolete components.
For more detailed information on all changes, visit the release notes or check out the list of new features in Xen 4.22 here.
