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Intel Nehalem also has a TLB bug Intel Nehalem also has a TLB bug
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Intel Nehalem also has a TLB bug
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Old 1st December 2008, 13:24   #1
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Default Intel Nehalem also has a TLB bug

We were pointed out that Intel's Nehalem, the CPU that we know as Core i7 has TLB. TLB, three letters that have destroyed the sales of Phenom and Opterons based on 65nm K10 cores stands for Translation Lookaside Buffer and Intel officialy states in its Intel Core i7 Processor, Extreme Edition Series and Intel Core i7 Processor - Specification Update PDF that the CPU has a TLB bug.

If you open Intelís official document that is nicely stored here, on page 37 AAJ1 Clarification of TRANSLATION LOOKASIDE BUFFERS (TLBS) Invalidation part, you will see that Intel tells that in some rare cases improper TLB invalidation may result in unpredictable system behaviour and can hang your OS or result with incorrect data. Here is the word to word "In rare instances, improper TLB invalidation may result in unpredictable system behavior, such as system hangs or incorrect data. Developers of operating systems should take this documentation into account when designing TLB invalidation algorithms. For the processors affected, Intel has provided a recommended update to system and BIOS vendors to incorporate into their BIOS to resolve this issue."

http://www.fudzilla.com/index.php?op...07&It emid=35
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Old 1st December 2008, 20:29   #2
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Intel Core 2 also...

Quote:
Chip bugs

The Core 2 memory management unit (MMU) in X6800, E6000 and E4000 processors does not operate to previous specifications implemented in previous generations of x86 hardware. This may cause problems, many of them serious security and stability issues, with existing operating system software. Intel's documentation states that their programming manuals will be updated "in the coming months" with information on recommended methods of managing the Translation Lookaside Buffer (TLB) for Core 2 to avoid issues, and admits that, "in rare instances, improper TLB invalidation may result in unpredictable system behavior, such as hangs or incorrect data."[55]

Among the issues noted:

* non-execute bit is shared across the cores.
* Floating point instruction non-coherencies.
* Allowed memory corruptions outside of the range of permitted writing for a process by running common instruction sequences.

Intel errata Ax39, Ax43, Ax65, Ax79, Ax90, Ax99 are said to be particularly serious.[56] 39, 43, 79, which can cause unpredictable behavior or system hang, have been fixed in recent steppings.

Among those who have noted the errata to be particularly serious are OpenBSD's Theo de Raadt[57] and DragonFly BSD's Matthew Dillon.[58] Taking a contrasting view was Linus Torvalds, calling the TLB issue "totally insignificant", adding, "The biggest problem is that Intel should just have documented the TLB behavior better."[59]

Microsoft has issued update KB936357 to address the errata by microcode update, with no performance penalty. BIOS updates are also available to fix the issue.
http://en.wikipedia.org/wiki/Intel_Core_2

might be much ado about nothing if BIOS update removes any problems from this bug without speed hit (like with Phenom)
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