The only way to prevent it on the current installed base of affected processors (Intel, ARM, maybe AMD or not) is to turn off speculative execution which could negatively affect performance (by as much as 30 percent).

I'm guessing the exploit is hard to use and unlikely to yield quick results.

It was criminal that the chip architects didn't think about this exploit (allowing speculative execution to bypass normal addressing checks enforced by virtual to physical address mapping (page table entries).

My understanding is that possibly some versions of Linux / Unix would not be open to the exploit due to how the address translation is set up (but I would have to defer to a Linux kernel expert on this).