I am aware that there is no microcode fix for Meltdown available (it has already been answered in various questions), and that the only extant microcode patches (IBRS and IPBP) only help with one of the Spectre variants, but I would like to know if a microcode fix for Meltdown is possible and feasible.
Specifically, I am curious whether or not:
- Intel's microcode implementation is sufficiently capable to mitigate Meltdown.
- Such a mitigation would be possible without an extreme performance hit.
- A microcode fix is practical enough that, in the future, one may be released.
- There is simply not enough public information to answer this question.
I already know that KPTI is the current "official" fix for Meltdown and that microcode and that new compiler instrumentation partially deal with Spectre. Disclaimer: I have not watched the 34c3 talk which may shed light on the limitations of Intel microcode, but I am aware that it has limitations.