Re: Linux 2.2.11pre2 proposed patch

Steve Dodd (dirk@loth.demon.co.uk)
Tue, 20 Jul 1999 14:49:52 +0100


On Tue, Jul 20, 1999 at 12:41:40PM +0100, BOSZORMENYI Zoltan wrote:

> Well, then will you please remove the f00f bugfix as well
> and develop a user space tool to switch it on?
> (The sarcastic taste was intended. :-))
> IMHO the processor bug workarounds should be in the
> the kernel.

I personally feel that all the (reasonably small) CPU workarounds should be
in the kernel, but I seem to have lost that battle. The idea that all the
distributions are going to include start-up scripts which grep /proc/cpuinfo
and run set6x86 accordingly is ludicrous wishful thinking IMHO.

To address your first point, I think the f00f bugfix has to be kernel space.
It seems to mess with mm things (does this indicate how little I understand
about it? :)

> And if the bugfix itself causes the file corruption then
> no matter where you enable the bugfix and which tool you use...

Note that there are two different techniques for working around the bug:

- set the NO_LOCK bit in CR<whatever>; can cause problems in obscure
circumstances (Alan mentioned a graphics / accelerator card problem)

- do some undocumented magic provided by (or reverse engineered from)
Cyrix, that seems to modify the CPU behaviour when executing the
offending instruction, making to do a noop afterwards. I don't know
of any problems caused by this.

-- 
%DCL-MEM-BAD, bad memory
VMS-F-PDGERS, pudding between the ears

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