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Patch Posted For Addressing The AMD CPU Performance Regression On Linux 6.15
As a follow-up to the Phoronix article a few days ago entitled A Linux 6.15 Performance Regression Hits Modern AMD CPUs, there continues to be activity to address this issue with the performance impact catching the upstream kernel developers off guard
As outlined in that earlier article after noting the Linux 6.15 regression and bisecting the issue, the change comes down to how an AMD SRSO security mitigation is applied for KVM. With Linux 6.15 the mitigation is applied simply if the KVM module is loaded on the system but not even running any virtual machines (VMs) where it's needed for the guest/host boundary protections. Use a dedicated mutex and counter instead of hooking virtualization enablement, as changing the behavior of kvm.enable_virt_at_load based on SRSO_BP_SPEC_REDUCE is painful, and has its own drawbacks, e.g. could result in performance issues for flows that are sensity to VM creation latency."
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