Red Hat Working On Optimizing KVM Virtualization Performance Stemming From Spectre

Red Hat's Andrea Arcangeli sent out an interesting patch series on Friday to micro-optimize the Kernel-based Virtual Machine (KVM) to enhance the VMEXIT performance in wake of Spectre mitigations. The "KVM monolithic" patch series ends up linking the KVM common code both into kvm-intel and kvm-amd so that the common "kvm" kernel module can be dropped. This occupies more disk space but should yield better run-time performance particularly for systems mitigated against Spectre Variant Two. For default Spectre V2 mitigations with Retpolines, this change has a surprising impact on the Intel and AMD virtualization performance for KVM. Andre noted, "This improves the vmexit performance by two digits percent on microbenchmarks with the spectre_v2 default mitigation on both VMX and SVM.