The many Kernel-based Virtual Machine (KVM) improvements have been merged for Linux 7.4 to deliver a number of new features for different server processors.
First up with KVM on Linux 7.4 is adding the initial ARM64 on IBM s390/Z support. This stems from the IBM and Arm collaboration aroound dual-architecture hardware and following that announcement earlier this year they began posting patches for ARM64 virtualization acceleration on IBM Z servers. Now in Linux 7.4 is that initial ARM64 on s390 support in the mainline kernel. Expect more improvements over the coming kernel cycles.
Over on the Intel side, the KVM code in Linux 7.4 enables Intel Instruction Timeout support formerly known as Notify VM-Exit. This is a security feature for mitigating possible denial of service attacks against servers with TDX-protected virtual machines. The attack vector mitigated is that a malicious guest VM could cause problems for the Linux server by blocking interrupt/event handling to starve host resources or locking up a CPU core.
Intel KVM support in Linux 7.4 also introduces Bus Lock VM Exit support for forcing a VM to exit to user-space whenever a guest CPU executes a bus lock instruction. This too is for preventing denial of service attacks and other performance concerns by malicious VMs.
On the AMD side with KVM for Linux 7.4 is support for Page Modification Logging (PML) for guests on AMD EPYC Zen 6 processors. This brings hardware-assisted dirty logging support to track guest-modified memory pages. This feature is enabled by default on capable EPYC Zen 6 server processors.
On the ARM side, there is pKVM state isolation support along with other pKVM enhancements. There is also more work on ARM confidential compute.
Another AMD virtualization improvement is support for virtualizing Bus Lock Detect on SVM.
The lengthy list of KVM changes for Linux 7.4 can be found via this pull request.