The lkml thread can be read, e.g., here. As for "simple instruction" , I see it this way:

Clearly, for some processors an update without reboot is dangerous, because it lead to situation when the kernel thinks that the processor support TSX, while in reality it was disabled by the update. Hence, the corresponding dangerous files in /lib/firmware/intel-ucode better not be created by the Slackbuild. Specialists who really know what they are doing can easily create them themselves. Since it not possible to be 100% sure on which files are safe, a simple solution is do not generate /lib/firmware/intel-ucode at all.

I feel that not generating /lib/firmware/intel-ucode is a better solution, but maybe this is because all my computers have "dangerous" processors.

Most programs will use the TSX instructions via glibc pthreads. The TSX stuff was added to glibc 2.18, but it's disabled by default unless --enable-lock-elision=yes is used. Slackware 14.1 uses glibc 2.17, and Slackware-current uses glibc 2.22 without --enable-lock-elision=yes, so in this case the non-early microcode loading should be safe on Haswell CPUs (though it's obviously better to use early microcode loading to avoid any potential problems in the future and IIRC it also prevents incorrect info in /proc/cpuinfo).

Also, from kernel 3.19 onwards, if early microcode is used, the kernel should reload it on resume from suspend (but I haven't confirmed so myself since I don't use suspend). Relevant commits are here and here.

Hi,

Well, we'll follow the Slackware principle here: if you're using nonstandard stuff, you're on your own.

I'd argue and say if you're dealing with microcode, you already should know something about what you're doing. If not, you'll learn quickly when the system crashes

So far, we know that TSX is a problem, but probably not for stock Slackware as this does not enable support for TSX in glibc. Are there any other potential users of TSX?

Asking more broadly, do you know of any other problems with microcode?

From what I read, there was/is a problem with coming back from suspend if you don't reapply the microcode. But I don't know if it's related to TSX or not.

For the moment, SlackBuild stays as it is (@slalik hates me).
Once I get more info, I can adjust the SlackBuild and/or add more info to the README.

--
Best regards,
Andrzej Telszewski