Mill Computing, Inc. › Forums › The Mill › Architecture › Meltdown and Spectre › Reply To: Meltdown and Spectre
On at least some architectures, you could use the spiller with the prefetching service to mitigate (not eliminate, but reduce the reliability of) cache snooping techniques. Since fast PLB lookups would drop
NaRs on the belt before the cache gets touched at all, the most reliable way to snoop would be to fill the cache, portal out (to the task switcher or the victim code), and then time loads when the portal call returns.
However, there’s nothing stopping you from spilling the cache line base addresses across calls, so you can reload the old cache data in advance of a predicted return. Of course, that reduces other processes’ ability to snoop.
Not sure how viable this is; regardless, it’s offered as an open-source technique, free of charge.
I came up with this while thinking about how to potentially fix Spectre on OOO machines; I was thinking about a scheme to eliminate the side-channel by tagging every cache line with the hardware turf that originated it, so that IPC could avoid a full cache invalidation, but then I realized that the attacker could still snoop to see which of their own lines were evicted so we’d need a full cache invalidation to hide it anyway.