linux-kernel - RE: [PATCH 4.4 10/24] x86/fpu: Hard-disable lazy FPU mode

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Message-ID: <000c01d40460$bfc97710$3f5c6530$@toshiba.co.jp>
Date:   Fri, 15 Jun 2018 13:24:27 +0900
From:   "Daniel Sangorrin" <daniel.sangorrin@...hiba.co.jp>
To:     "'Greg Kroah-Hartman'" <gregkh@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>
Cc:     <stable@...r.kernel.org>, "'Andy Lutomirski'" <luto@...nel.org>,
        "'Rik van Riel'" <riel@...hat.com>,
        "'Borislav Petkov'" <bp@...en8.de>,
        "'Brian Gerst'" <brgerst@...il.com>,
        "'Dave Hansen'" <dave.hansen@...ux.intel.com>,
        "'Denys Vlasenko'" <dvlasenk@...hat.com>,
        "'Fenghua Yu'" <fenghua.yu@...el.com>,
        "'H. Peter Anvin'" <hpa@...or.com>,
        "'Josh Poimboeuf'" <jpoimboe@...hat.com>,
        "'Linus Torvalds'" <torvalds@...ux-foundation.org>,
        "'Oleg Nesterov'" <oleg@...hat.com>,
        "'Peter Zijlstra'" <peterz@...radead.org>,
        "'Quentin Casasnovas'" <quentin.casasnovas@...cle.com>,
        "'Thomas Gleixner'" <tglx@...utronix.de>, <pbonzini@...hat.com>,
        "'Ingo Molnar'" <mingo@...nel.org>
Subject: RE: [PATCH 4.4 10/24] x86/fpu: Hard-disable lazy FPU mode

Hi Greg,

>  /* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
> --- a/arch/x86/include/asm/fpu/internal.h
> +++ b/arch/x86/include/asm/fpu/internal.h
> @@ -58,7 +58,7 @@ extern u64 fpu__get_supported_xfeatures_
>   */
>  static __always_inline __pure bool use_eager_fpu(void)
>  {
> -	return static_cpu_has_safe(X86_FEATURE_EAGER_FPU);
> +	return true;
>  }

Since this function returns always true then we can remove the code depending on lazy FPU mode.
Actually this has already been done in "x86/fpu: Remove use_eager_fpu()"
Ref: https://patchwork.kernel.org/patch/9365883/

>  static void __init fpu__init_parse_early_param(void)
>  {
> -	if (cmdline_find_option_bool(boot_command_line, "eagerfpu=off")) {
> -		eagerfpu = DISABLE;
> -		fpu__clear_eager_fpu_features();
> -	}

Since this patch removes the kernel boot parameter "eagerfpu", maybe we should remove it from the Documentation.
This has also been done by commit "x86/fpu: Finish excising 'eagerfpu'"
Ref: https://patchwork.kernel.org/patch/9380673/

I will try backporting those patches unless anyone has any objections.

Thanks,
Daniel Sangorrin