Re: [PATCH 1/10] Cr4 is valid on some 486s

[Eric W. Biederman]

Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> writes:

> On Sul, 2005-11-13 at 11:59 +0100, Andi Kleen wrote:
>> Dave Jones <davej@xxxxxxxxxx> writes:
>> > 
>> > Looks like the Ubuntu people already did this...
>> > 
>> >
> http://www.kernel.org/git/?p=linux/kernel/git/bcollins/ubuntu-2.6.git;a=commitdiff;h=048985336e32efe665cddd348e92e4a4a5351415;hp=1cb630c2b5aaad7cedaa78aa135e6cecf5ab91ac
>> 
>> It's probably not needed. At least AMD K7/K8 has a SYSCFG MSR bit to
>> do this (or rather they disable bus cycles for locks that makes them
>> very cheap) Intel has one too in a different MSR that looks similar.
>> With some luck they're even already set by the BIOS on UP systems.  I
>> know they are on some AMD systems.
>
> I'd hope the vendors are not doing that by default because we have
> kernel code that uses lock against not other processors but other bus
> masters. The ECC code is one example. Is there any good info on the AMD
> one so I can make the EDAC code put the processor back in x86 compatible
> mode so that it behaves safely when scrubbing.

Check out the AMD's BIOS and Kernel Programmer Guide for the K8.  The
appropriate bits are documented, although the documentation is quite
terse.

Eric

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