I'm willing to bet that it's impossible to fix meltdown with microcode, because the bug is not in a microcoded part of the CPU. In the future, we might see OS

I'm willing to bet that it's impossible to fix meltdown with microcode, because the bug is not in a microcoded part of the CPU. In the future, we might see OS optimisations that work around the slowdowns by doing even less syscalls, but KPTI will stay until meltdown is fixed in silicon (which won't happen for 2-4 years)