The Performance Hit For A Xeon-Backed Ubuntu Linux VM With L1TF / Foreshadow Patches

The Stress-NG Linux kernel benchmarks also show off some of the possible performance implications of this mitigation.

Under sysbench the performance only took a measurable hit with the fully mitigated approach where Hyper Threading is no longer available.

The Apache performance was only slightly impacted by the default mitigation approach but more so under the "always flushing" and full mitigation levels.

In most workloads, the default mitigation for L1 Terminal Fault / Foreshadow yielded up to a few percent performance impact in the default behavior for this mitigation that only should impact the virtual machine performance and not the bare metal system's performance abilities. Obviously when switching to unconditional L1D cache flushing the performance tended to have a more profound performance cost while if opting for the "full" mitigation that disables SMT there is a very sizable performance impact for VMs due to losing out on Hyper Threading. Additional tests are currently running as we continue exploring the performance cost of L1TF/Foreshadow.