Last I checked: the linux kernel initially had a comment saying something to the effect of "assume all x86 processors are vulnerable." Later, they added a chec

Last I checked: the linux kernel initially had a comment saying something to the effect of "assume all x86 processors are vulnerable." Later, they added a check for amd, which they don't do mitigations on. It seems likely they'll add another check, when future processors come out. As for windows and macosx, it's up for speculation. No other OSes yet have mitigations in place.