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

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Message-ID: <20150630051759.GC5782@gmail.com>
Date:	Tue, 30 Jun 2015 07:18:00 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	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


* H. Peter Anvin <hpa@...or.com> wrote:

> 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.

Yeah, so the patch I sent to Mike (and which solved the bug) moved it to [5].

Thanks,

	Ingo
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