I just noticed that there is another leftover regarding FRED:
arch/x86/kernel/cpu/cpuid-deps.c:86: { X86_FEATURE_FRED, X86_FEATURE_WRMSRNS },
We removed the dependency on X86_FEATURE_WRMSRNS, right? So this is
stale and should be removed too.
Right, I did plan to include such a change per your ask to remove the
comment in arch/x86/include/asm/switch_to.h:
https://lore.kernel.org/lkml/87ttfw18jy.ffs@tglx/
So it will be in the next iteration of that patch set.