linux-kernel - Re: [tip:x86/asm] x86/fpu: Fix early FPU command-line parsing

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Date:	Fri, 15 Jan 2016 12:50:35 -0800
From:	Yu-cheng Yu <yu-cheng.yu@...el.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	torvalds@...ux-foundation.org, tglx@...utronix.de, oleg@...hat.com,
	ravi.v.shankar@...el.com, fenghua.yu@...el.com, mingo@...nel.org,
	dave.hansen@...ux.intel.com, quentin.casasnovas@...cle.com,
	bp@...e.de, hpa@...or.com, luto@...capital.net,
	sai.praneeth.prakhya@...el.com, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/asm] x86/fpu: Fix early FPU command-line parsing

On Fri, Jan 15, 2016 at 09:28:58PM +0100, Borislav Petkov wrote:
> > +static void __init fpu__init_parse_early_param(void)
> > +{
> > +	/*
> > +	 * No need to check "eagerfpu=auto" again, since it is the
> > +	 * initial default.
> > +	 */
> > +	if (cmdline_find_option_bool(boot_command_line, "eagerfpu=off"))
> > +		eagerfpu = DISABLE;
> > +	else if (cmdline_find_option_bool(boot_command_line, "eagerfpu=on"))
> > +		eagerfpu = ENABLE;
> > +
> > +	if (cmdline_find_option_bool(boot_command_line, "no387"))
> > +		setup_clear_cpu_cap(X86_FEATURE_FPU);
> > +
> > +	if (cmdline_find_option_bool(boot_command_line, "nofxsr")) {
> > +		setup_clear_cpu_cap(X86_FEATURE_FXSR);
> > +		setup_clear_cpu_cap(X86_FEATURE_FXSR_OPT);
> > +		setup_clear_cpu_cap(X86_FEATURE_XMM);
> > +	}
> > +
> > +	if (cmdline_find_option_bool(boot_command_line, "noxsave"))
> > +		fpu__xstate_clear_all_cpu_caps();
> > +
> > +	if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
> > +		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
> > +
> > +	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
> > +		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
> 
> This could certainly be improved: we're iterating over the *whole*
> command line each time for each option unconditionally instead of
> iterating word by word and comparing it with all strings.
> 
> We'd need something like cmdline_for_each_word() or so, though...
> 

That is a good point. I will work on it.

Thanks,
Yu-cheng