Looking At The LVI Mitigation Impact On Intel Cascade Lake Refresh

Intel has publicly said they believe LVI to be mostly a hypothetical attack.

But if production software ends up making use of the LLVM mitigation or that to other toolchains like we have also seen out of GNU, the performance hit is very sizable due to all of the additional load fence instructions.

When firing up over 50 C/C++ tests for comparing this LVI mitigation in LLVM, the geometric mean of all the benchmarks on the current Clang 11 code with this Intel Xeon Scalable Cascade Lake Refresh server amounted to a 20% performance hit. Thankfully though for performance sake this mitigation is not enabled by default and hopefully LVI will only remain a theoretical attack, but we'll leave it up to the security experts for their recommendations on building software with these mitigations.