linux-kernel - Re: i387/FPU init issues...

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Date:	Sat, 03 May 2008 13:02:03 -0400
From:	jamal <hadi@...erus.ca>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Jan Beulich <jbeulich@...ell.com>
Subject: Re: i387/FPU init issues...

On Sat, 2008-03-05 at 17:31 +0200, Thomas Gleixner wrote:
> On Sat, 3 May 2008, jamal wrote:
> >  =======================
> > Code: 8d 74 26 00 8d bc 27 00 00 00 00 55 89 c2 8b 40 04 89 e5 f6 40 0c
> > 01 74 32 8b 82 60 02 00 00 0f ae 00 0f ba 60 02 07 73 02 db e2 <0f> 1f
> > 00 90 8d b4 26 00 00 00 00 89 f6 8b 42 04 83 60 0c fe 0f
> 
> This looks bad.
> 
>   0f ae 00		fxsave (%eax)
>   0f ba 60 02 07       	btl    $0x7,0x2(%eax)
>   73 02                	jae    (skip fnclex)
>   db e2                	fnclex 
>   0f 1f 00             	nopl   (%eax)
> 
>  ^^^^ This is a P4+ instruction. So it's not surprising that the P2
>  chokes. The question is where this comes from.
> 
> we have:
> #define P6_NOP3 ".byte 0x0f,0x1f,0x00\n"

Dang - I feel i should have saved myself all that git bisecting
and just posted the oops ;->

> So the alternatives code applies the wrong nop padding for your
> CPU. This was probably introduced with commit
> 32c464f5d9701db45bc1673288594e664065388e. 
> 
> Jan, are you sure that P3 knows the P6 NOPs ? AFAICT its P4, but I
> have to dig up the manuals.
> 
> Jamal, does the following patch solve your problem ? 


Indeed it does - thanks.

> Please provide
> also output of /proc/cpuinfo.

mambo:~# cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 3
model name      : Pentium II (Klamath)
stepping        : 3
cpu MHz         : 1063.771
cache size      : 128 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu de pse tsc msr pae mce cx8 sep pge cmov mmx fxsr
sse sse2
bogomips        : 2160.92
clflush size    : 32
power management:

cheers,
jamal

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