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

[Daniel Sangorrin]

> -----Original Message-----
> From: stable-owner@xxxxxxxxxxxxxxx [mailto:stable-owner@xxxxxxxxxxxxxxx] On
> Behalf Of 'Greg Kroah-Hartman'
> Sent: Friday, June 15, 2018 1:56 PM
> To: Daniel Sangorrin <daniel.sangorrin@xxxxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx; 'Andy Lutomirski'
> <luto@xxxxxxxxxx>; 'Rik van Riel' <riel@xxxxxxxxxx>; 'Borislav Petkov'
> <bp@xxxxxxxxx>; 'Brian Gerst' <brgerst@xxxxxxxxx>; 'Dave Hansen'
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> 'Fenghua Yu' <fenghua.yu@xxxxxxxxx>; 'H. Peter Anvin' <hpa@xxxxxxxxx>; 'Josh
> Poimboeuf' <jpoimboe@xxxxxxxxxx>; 'Linus Torvalds'
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> Zijlstra' <peterz@xxxxxxxxxxxxx>; 'Quentin Casasnovas'
> <quentin.casasnovas@xxxxxxxxxx>; 'Thomas Gleixner' <tglx@xxxxxxxxxxxxx>;
> pbonzini@xxxxxxxxxx; 'Ingo Molnar' <mingo@xxxxxxxxxx>
> 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