KVM Changes Land In Linux 5.16: RISC-V Hypervisor Support, AMD PSF Control Bit
Written by Michael Larabel in Virtualization on 8 November 2021 at 05:47 AM EST. 1 Comment
VIRTUALIZATION --
Last week the Kernel-based Virtual Machine (KVM) feature patches were sent out and subsequently merged for Linux 5.16.

Arguably most notable for KVM with Linux 5.16 is the introduction of the RISC-V architecture code for the Kernel-based Virtual Machine. The KVM RISC-V hypervisor support depends upon the RISC-V ISA's hypervisor extension, which was recently frozen. Now to wait for RISC-V processors to market that are performant and supporting the extension...

Over on the x86 (x86_64) side, there are various minor improvements to the code. One user-facing change for AMD SVM is support for turning off AMD PSF to KVM guests. PSF is Predictive Store Forwarding with Zen 3 and what was disclosed earlier this year as possible security implications. The AMD PSF toggle patch to outright disable it has yet to be merged to the Linux kernel while for 5.16 is now the patch to at least allowing the PSF control bit to be toggled by guest kernels.

KVM on the Arm front has continued its enablement around protected virtual machines. There are also workarounds for the Apple M1 with a broke VGIC implementation. The KVM s390 code has also seen various improvements, including work around handling for lazy destroying of secure VMs.

The full list of KVM patches so far for Linux 5.16 can be found via this mailing list post. A second batch of KVM changes for this new kernel are likely to be posted this week.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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