The Kernel-based Virtual Machine changes for [1]Linux 6.9 continue to enhance the capabilities of the open-source Linux virtualization software stack.

For KVM on x86 (x86_64) there is an optimization to triggering of emulated events. Developers found this provides a nice approximate 10% performance improvement for VM-Exit micro-benchmarks.

There is also some improvements as a result of reworking the code around "force immediate exit" on x86_64 so that vendor code decides how and when to force the exit. This allows optimizations for both AMD and Intel processors.

There are also various other smaller optimizations and code improvements. The KVM x86 Xen emulation code has also seen some improvements for Linux 6.9.

Another change worth noting from the KVM pull request is AMD now reports a "ept_5level" flag in /proc/cpuinfo for VMX supporting 5-level EPT paging. This user-space ability to query 5-level paging support is important since the MSRs indicating support aren't easily accessible by user-space. This information is needed so user-space can correctly configure KVM virtual machines on AMD 5-level paging configurations.

Over on the KVM RISC-V side is support for the Ztso and Zacas extensions. LoongArch and ARM have also seen various minor enhancements this cycle.

More details on the KVM changes for Linux 6.9 via [2]this pull that was already merged. Linux 6.9-rc1 should be out later today to culminate the Linux 6.9 merge window.



[1] https://www.phoronix.com/search/Linux+6.9

[2] https://lore.kernel.org/lkml/20240315174939.2530483-1-pbonzini@redhat.com/T/#u