At least based on my tests it is not possible to remove the impact of the mitigations with boot-time flags: this "disabled" the mitigations but the code paths f

At least based on my tests it is not possible to remove the impact of the mitigations with boot-time flags: this "disabled" the mitigations but the code paths for eg for kernel calls is still much different and slower than pre-mitigation kernels. Pre-mitigation I measured just over 100 ns for a bare do-nothing system call, while after it is over 1,000. However if you disable mitigations on the boot command line I still see over 500 ns so it is not close to the old performance. You'd have to run an old kernel to really get pre-mitigation performance. I tested this just after Meltdown + Spectre 1-3, so things may have better or worse since then, I'm not sure.