DragonFly BSD
DragonFly kernel List (threaded) for 2012-03
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AMD cpu bug update -- AMD confirms! (additional info)

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Tue, 6 Mar 2012 16:46:59 -0800 (PST)

    Upfront before people dive this please note that Bulldozer is NOT
    effected by this bug.

    I talked with AMD a bit more after it got slashdotted and they suggested
    that I include the second paragraph as well, because the slashdotting
    created some confusion.  I posted the clarification to slashdot
    which I will include here.  Here are both paragraphs:

	AMD has taken your example and also analyzed the segmentation
	fault and the fill_sons_in_loop code. We confirm that you have
	found an erratum with some AMD processor families. The specific
	compiled version of the fill_sons_in_loop code, through a very
	specific sequence of consecutive back-to-back pops and (near)
	return instructions, can create a condition where the processor
	incorrectly updates the stack pointer.

	AMD will be updating the Revision Guide for AMD Family
	10h Processors and the Revision Guide for AMD Family
	12h Processors, to document this erratum. In this documentation
	update, which will be available on amd.com<http://amd.com/> later
	this month, the erratum number for this issue will be #721. The
	revision guide will also note a workaround that can be programmed
	in a model-specific register (MSR).

    (and in another email):

	Bulldozer processors, by the way, do not have this erratum.

    I don't know precisely which of the older family processors has the bug.
    We will all have to wait for the errata to come out to get that info.
    I can only attest to the two specific cpus I was testing on
    (a Phenom II X4 820 and a quad-socket Opteron 6118 = 48 cores).
    However, AMD has told me specifically that Bulldozer is NOT effected.

    Here is a reference to the email I posted to the DragonFly lists
    in December outlining my suspicions, for additional background on
    what it took to narrow the bug down:



    Again, while this is certainly a serious cpu bug it looks like there
    will be a MSR fix for it on the older cpus.  We will all have to wait
    for AMD to finalize and publish the errata, now.

					Matthew Dillon 

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