KVM Preps For New Intel CPU Instructions With Linux 6.2

Written by Michael Larabel in Virtualization on 16 December 2022 at 12:00 AM EST. Add A Comment
The initial batch of feature updates for the Kernel-based Virtual Machine (KVM) have been submitted for the Linux 6.2 merge window.

As usual there is a wide assortment of KVM enhancements with this next kernel version and also fairly as usual when it comes to hardware/architecture-specific changes does tilt in favor of x86_64 and ARM64 work.

KVM for x86/x86_64 now allows compiling without the System Management Mode (SMM) support, various Hyper-V improvements, advertising of new Intel CPU instructions, and other fixes/optimizations. Among the new Intel CPU instructions that can be properly advertised to guests are AMX-FP16, AVX-IFMA, AVX-VNNI-INT8, AVX-NE-CONVERT, PREFETCHIT0/1, and CMPccXADD. Intel engineers have been busy preparing these new instructions in the LLVM/Clang and GCC compilers, Linux kernel, and related components ahead of next-generation processors coming with these instructions over the next two years.

KVM with Linux 6.2 adds a new FOLL_INTERRUPTIBLE flag with support for responding to signals during page faults. This started after a bug report over libvirt being unable to stop a virtual machine using the "stop" QMP command during a paused post-copy migration of a virtual machine.

The AArch64 (ARM64) code has seen a number of improvements including the enabling of the per-vCPU dirty-ring tracking mechanism, switching to relaxed parallel fault handling, relaxing the memory tagging extension (MTE) ABI, support for the PMUv3p5 architecture revision, and various fixes. The relaxed parallel fault handling for ARM64 should help enhance the AArch64 KVM performance under system load.

The full list of KVM updates for Linux 6.2 can be found via this pull request.
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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, LinkedIn, or contacted via MichaelLarabel.com.

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