Tracking Down The AMD "Processor Bug"

tercero writes: "over at the Gentoo Linux website there is an update on the AMD processor bug mentioned here. The sum up is that AMD claims it's not a bug with the Athlon processor, but with the motherboard. More detailed information can be found on this LKML post." An Anonymous Coward points to a similar explanation at Linux Weekly News. Update: 01/25 01:25 GMT by T : Daniel Robbins from Gentoo clarifies: "AMD is not calling this a 'motherboard' issue, it is an interaction between a feature of the Athlon called 'speculative writes' and the design of the GART, which is not cache-coherent. It's a 'Athlon/cache coherency/GART' problem, not a 'motherboard' problem."

Comments

Don't blame AMD entirely

[ekrout]

Don't blame AMD entirely. They acknowledged the bug back in September of 2000 and immediately released patches for Windows 2000. Consequently, it doesn't affect users of Windows XP either. It's been around for over a year and now it's "news"? This should've been fixed in the Linux kernel months ago. Sorry for sounding so harsh.

Re:It is (not?) a CPU bug.

[tommck]

If the bug doesn't appear on intel chips, then how are we supposed to believe that it's not an AMD bug?

Well, based on my reading of other posts, it is a simple case of AMD taking advantage of some features of AGP that are within spec that Intel is not. When the OS assumes that things are done Intel's way instead of adhering to the spec, things will show up on an AMD processor and not on an Intel.

AMD is doing things correctly, albeit differently from Intel. This is exactly how we are supposed to believe that it's not an AMD bug.

T

You are assuming...

[Arker]

You are assuming that AMDs current explanation is 100% true, correct, and complete. There are good reasons to doubt this.

The "explanation" so far has just raised more questions. Why does the same code that causes the athlon to crash work fine on pentiums? Apparently the GART is cacheable on pentium systems? And the Athlon is billed as pentium-compatible...

Why does disabling large pages fix the problem? If their explanation is correct, that fix should not work, because it doesn't address the issue they claim to be the problem.

I'm sure this will get worked around in software (and the linux fix will actually workaround the underlying problem, rather than just making it less likely as the windows world seems to be satisfied with) once the real details of this are known. But to claim it's not a hardware bug is ludicrous. It's a bug with the Athlon CPU, or with certain GARTS found in Athlon chipsets, or both. If AMD were less worried about spin-controlling it and claiming it's the software at fault maybe they would be more forthcoming about what is really going on here.