From: Michal Marek
Date: Tue Jan 19 2016 - 07:43:31 EST

Dne 19.1.2016 v 13:29 Måns Rullgård napsal(a):
> Force-enabling BLK_DEV_INITRD isn't going to make anyone change their
> boot scripts.

If you are on a regular distro, /sbin/installkernel should do the right
thing: Run mkinitrd / dracut and if the tools are recent enough and
there is a microcode update for your CPU, a cpio with the microcode blob
will be prepended to the initrd. So this is more or less covered.

> I'd also like to get a coherent answer to why microcode update is
> preferably done from an initrd as opposed to shortly after mounting
> a regular disk. My systems seem perfectly happy doing the latter.

It's not even done *from* the initrd but way earlier. We learned the
hard way when Intel released a microcode update for Haswell which
disabled TSX: Userspace did not expect the feature flags to change and
previously valid instructions to start trapping. This can in principle
happen again and with any vendor.