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Is hyperthreading dangerous?

Is hyperthreading dangerous?

Posted May 19, 2005 15:13 UTC (Thu) by khim (subscriber, #9252)
In reply to: Is hyperthreading dangerous? by filipjoelsson
Parent article: Is hyperthreading dangerous?

Does this very theoretical exploit affect multicore systems too?

Yes and no. Yes - it's possible to use the same technique for dual-core systems. But in reality it'll require way too much brute force. The problem with Hyper-Threading is size of L1 cache - it's too small. Multicore systems only share L2 cache (if even that) and it's much bigger so problem becomes pure theory.

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Dual cores...

Posted May 26, 2005 13:30 UTC (Thu) by MarkWilliamson (subscriber, #30166) [Link]

IIRC, the initial dual-cores from AMD and Intel will not share any cache.
Intel's (initial) implementation in particular is basically two
independent CPUs on the same die. Even when shared L2 caches are
implemented, it seems that sharing an L2 cache will provide lower
bandwidth to this kind of exploit, which benefits hugely from the shared
L1 cache of the two hyperthreads.

Note that IBM's POWER4 shares caches across multiple cores and the POWER5
also has SMT...

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