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Comment by hlandau | Hacker News Reader

This seems to contradict the previous assertions that AMD CPUs aren't affected.

Branch prediction is related to the Spectre attack. I believe AMD is only unaffected by Meltdown.

Disabling branch prediction isn't mitigation it is effectively a recall without having to worry about logistics because if you disable branch prediction completely you might as well throw Zen based CPUs to the trash.

I really hope that this is just poor wording and that branch prediction is either disabled in extremely rare circumstances or they just exposed some control mechanism like Intel did which allows you to control the branching.

EDIT:

AMD's response was that mitigation from their side isn't needed for SPECTRE either:

http://www.guru3d.com/news-story/amd-rsponds-on-amd-processo...

I really wonder what has changed, and if now they are vulnerable to variant 2, have they underestimated MELTDOWN as well?

I'm also looking forward for people to look into the victim cache that AMD has implemented with Zen and if InfinityFabric and the added latency between CCXs can't be exploited for side channels attacks.

I might be reading that link wrong, but it looks like it says that Variant 2 is a possibility, just not demonstrated yet. This may be preemptive on their end.. or maybe they were able to replicate it in-house.

That's because those previous assertions were incorrect.

AMD is not affected by Meltdown, true, but Meltdown is also easier to fix. The other issues do affect AMD, and are MUCH harder to fix (also harder to use it should be pointed out).

Meltdown was disclosed first, so everyone was excited to bash Intel. But that was premature.

Intel is affected by spectre as well though.

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