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Date: Fri, 15 Jan 2016 12:50:35 -0800
From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
        torvalds@linux-foundation.org, tglx@linutronix.de, oleg@redhat.com,
        ravi.v.shankar@intel.com, fenghua.yu@intel.com, mingo@kernel.org,
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        hpa@zytor.com, luto@amacapital.net, sai.praneeth.prakhya@intel.com,
        linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/asm] x86/fpu: Fix early FPU command-line parsing
Message-ID: <20160115205035.GA32625@test-lenovo>
References: <1452119094-7252-2-git-send-email-yu-cheng.yu@intel.com>
 <tip-4f81cbafcce2c603db7865e9d0e461f7947d77d4@git.kernel.org>
 <20160115202858.GK25104@pd.tnic>
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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