[cesarb]

According to https://access.redhat.com/articles/3311301 PTI should be enabled on Intel even with the new microcode, so the microcode update probably doesn't fix variant 3 (Meltdown).

Also, I don't think the microcode updates just expose some chicken bits. IBRS seems to be exposing one or more chicken bits as a single bit, but IBPB seems to be a command to run a routine in the microcode to immediately clear part of the branch predictor state, not a chicken bit.

Yes, the kernel changes in the Linus tree only fix variant 3, there are several partial and/or mutually incompatible patch sets being posted on the linux kernel mailing list to fix the other variants; the Red Hat kernel seems to have an early version of some of these. See also the just posted http://kroah.com/log/blog/2018/01/06/meltdown-status/ for more detail.

[usernam]

I read both, and I can confirm that meltdown is not fixed by the microcode update alone. But I'm confused by intel claiming a fix for all three variants of exploits: I would have realistically expected a proper fix for meltdown, but it seems that intel can't really fix it in microcode.