linux-kernel - Re: [all better] Re: regression: massive trouble with fpu rework

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Message-ID: <1435461117.3418.32.camel@gmail.com>
Date:	Sun, 28 Jun 2015 05:11:57 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [all better] Re: regression: massive trouble with fpu rework

On Sat, 2015-06-27 at 18:02 -0300, Henrique de Moraes Holschuh wrote:
> On Sat, 27 Jun 2015, Mike Galbraith wrote:
> > > > BIOS setting "Limit CPUID Maximum" upsets new fpu code mightily.
> > 
> > That BIOS setting is annotated with the helpful text "Disabled for
> > Windows XP".  It makes box say interesting things during boot, like...
> > 
> >         x86/fpu: XSTATE_CPUID missing!
> > 
> > 
> > ..or with HEAD, it triggers warning..
> > 
> >         if (boot_cpu_data.cpuid_level < XSTATE_CPUID) {
> >                 WARN_ON_FPU(1);
> >                 return;
> >         }
> > 
> > ..and all kinds of bad juju follows.  I have no idea what the thing does
> > beyond what I can interpolate from the word 'limit'.
> 
> Well, it is supposed to disable CPUID levels >= 0x04.  This thing should
> *NEVER* be enabled, the last operating system that required it to be enabled
> was Windows 98.
> 
> Can/do we override that crap during cpu init?  If we cannot/don't, maybe
> instead of limping along with CPUID crippled, it would be better to either
> output a very nasty warning, or outright stop booting [with an appropriate
> error message] ?

Why get all upset?  We didn't even notice before, nor did/does that
other OS.  A casual "BTW, your BIOS sucks.." should suffice, no?

	-Mike

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