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

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Message-ID: <5591A177.7050802@zytor.com>
Date:	Mon, 29 Jun 2015 12:50:15 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>, Dave Hansen <dave@...1.net>
Subject: Re: [all better] Re: regression: massive trouble with fpu rework

On 06/28/2015 11:40 PM, Ingo Molnar wrote:
> 
> Ok, so could you please move the fpu__init_system() further up and see which 
> position is that starts breaking with the BIOS option set?
> 
> here's the current, broken layout of the code:
> 
>         get_cpu_cap(c);
> [0]     fpu__init_system(c);
> 
>         if (this_cpu->c_early_init)
>                 this_cpu->c_early_init(c);
> 
> [1]
>         c->cpu_index = 0;
> [2]
>         filter_cpuid_features(c, false);
> 
> [3]
>         if (this_cpu->c_bsp_init)
>                 this_cpu->c_bsp_init(c);
> 
> [4]
>         setup_force_cpu_cap(X86_FEATURE_ALWAYS);
> [5]
> }
> 
> and we know it from your testing that moving [0] to [5] fixes the crash.
> 
> The question is, can we move it to [4], [3], [2] or even [1] instead, without 
> breaking the system?
> 
> I still don't see where the breakage comes from, but this would help us narrow it 
> down.
> 

It should be moved to [4] or [5].  I would argue that the line setting
X86_FEATURE_ALWAYS should moved up and then fpu__init_system(c) should
be moved after the c_bsp_init() line.

	-hpa


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