linux-kernel - Re: x86 fpu: command-line parameters broken post-FPU-rewrite

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Message-ID: <20151209191411.GC10475@pd.tnic>
Date:	Wed, 9 Dec 2015 20:14:11 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: x86 fpu: command-line parameters broken post-FPU-rewrite

On Wed, Dec 09, 2015 at 09:32:10AM +0100, Ingo Molnar wrote:
> 
> * Dave Hansen <dave.hansen@...el.com> wrote:
> 
> > Hey Ingo,
> > 
> > We were starting to look at reenabling XSAVES support and tried to use the 
> > 'noxsave' and 'noxsaves' kernel command-line options.  The rewrite moved the FPU 
> > initialization to before we even are parsing command-line options, even the 
> > early_param()s.
> > 
> > Do you have any preferences on how it gets fixed?
> > 
> > The most obvious thing would be to just defer as much of the FPU setup as we can 
> > until after parse_early_param() has happened.  The only other think I can think 
> > of doing would be to try to do some *really* early, simple, command-line parsing 
> > to look for 'noxsave' and friends.
> > 
> > Thoughts?
> 
> Hm, so given that having the FPU operational is key to a functioning kernel (and 
> other kernel subsystems may make use of FPU functionality), I'd rather bring 
> option parsing earlier than change the FPU setup sequence. FPU setup should be 
> done when we identify the CPU - not 'very late' as we used to.

We already have early cmdline parsing: arch/x86/lib/cmdline.c

See users for examples.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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