It is no longer valid to not replace instructions, since we depend on
different behaviour depending on CPU capabilities.

If you need to limit the capabilities of the replacements (because the
boot CPU has features that non-boot CPU's do not have, for example), you
need to explicitly disable those capabilities that are not shared across
all CPU's.

For example, if your boot CPU has FXSR, but other CPU's in your system
do not, you need to use the "nofxsr" kernel command line, not disable
instruction replacement per se.