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

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Date:   Fri, 15 Jun 2018 14:23:08 +0900
From:   "Daniel Sangorrin" <daniel.sangorrin@...hiba.co.jp>
To:     "'Greg Kroah-Hartman'" <gregkh@...uxfoundation.org>
Cc:     <linux-kernel@...r.kernel.org>, <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

> -----Original Message-----
> From: stable-owner@...r.kernel.org [mailto:stable-owner@...r.kernel.org] On
> Behalf Of 'Greg Kroah-Hartman'
> Sent: Friday, June 15, 2018 1:56 PM
> To: Daniel Sangorrin <daniel.sangorrin@...hiba.co.jp>
> Cc: linux-kernel@...r.kernel.org; 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
> 
> On Fri, Jun 15, 2018 at 01:24:27PM +0900, Daniel Sangorrin wrote:
> > 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.
> 
> What are the git commit ids of those patches in Linus's tree?  No need
> to point to patchwork links, I don't use that tool.

OK, I got it.

"x86/fpu: Remove use_eager_fpu()": c592b57347069abfc0dcad3b3a302cf882602597
"x86/fpu: Finish excising 'eagerfpu'": e63650840e8b053aa09ad934877e87e9941ed135

Unfortunately, they don't apply cleanly to stable kernels.

Thanks,
Daniel Sangorrin