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

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Date:	Sat, 3 May 2008 19:39:57 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ingo Molnar <mingo@...e.hu>
cc:	jamal <hadi@...erus.ca>, Suresh Siddha <suresh.b.siddha@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	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, 3 May 2008, Ingo Molnar wrote:
> * jamal <hadi@...erus.ca> wrote:
> 
> > > 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 ;->
> 
> your bisection was still very useful - it pinpointed the NOPs - the 
> assembly code around the NOP changed so a different length NOP was 
> patched in => which did not work on your CPU. So thanks for that! The 
> fix is already in x86.git (we'll update the commit log).
> 
> > > 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.
> 
> great. So this NOP is indeed not generally known to all "P6 and later" 
> CPUs. (the PII)

Looks like. My analysis was wrong, as I got the P6 vs. PII/PIII
confused :) Damn unintutive numbering, I thought ARM is worse but I'm
not so sure anymore.

But the oops clearly identified that instruction sequence. So for now
we remove the X86_FEATURE_P3 -> P6_NOPS to be on the safe side.

Thanks,
	tglx
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