The "What If" Performance Cost To Kernel Page Table Isolation On AMD CPUs

Made public this week by CPU security researchers at Graz University of Technology and CISPA Helmholtz Center for Information Security was the research paper published "AMD Prefetch Attacks through Power and Time". The paper points to AMD CPUs suffering from a side-channel leakage vulnerability through timing and power variations of the PREFETCH instruction. The paper argues that AMD CPUs should activate stronger page table isolation by default. AMD has now published their security response where they are not recommending any mitigation changes at this time. But what if Kernel Page Table Isolation (KPTI/PTI) proves necessary for AMD CPUs? Here are some initial benchmarks showing what that performance impact could look like.