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SubjectRE: [PATCH 4.4 10/24] x86/fpu: Hard-disable lazy FPU mode
Date
> -----Original Message-----
> From: stable-owner@vger.kernel.org [mailto:stable-owner@vger.kernel.org] On
> Behalf Of 'Greg Kroah-Hartman'
> Sent: Friday, June 15, 2018 1:56 PM
> To: Daniel Sangorrin <daniel.sangorrin@toshiba.co.jp>
> Cc: linux-kernel@vger.kernel.org; stable@vger.kernel.org; 'Andy Lutomirski'
> <luto@kernel.org>; 'Rik van Riel' <riel@redhat.com>; 'Borislav Petkov'
> <bp@alien8.de>; 'Brian Gerst' <brgerst@gmail.com>; 'Dave Hansen'
> <dave.hansen@linux.intel.com>; 'Denys Vlasenko' <dvlasenk@redhat.com>;
> 'Fenghua Yu' <fenghua.yu@intel.com>; 'H. Peter Anvin' <hpa@zytor.com>; 'Josh
> Poimboeuf' <jpoimboe@redhat.com>; 'Linus Torvalds'
> <torvalds@linux-foundation.org>; 'Oleg Nesterov' <oleg@redhat.com>; 'Peter
> Zijlstra' <peterz@infradead.org>; 'Quentin Casasnovas'
> <quentin.casasnovas@oracle.com>; 'Thomas Gleixner' <tglx@linutronix.de>;
> pbonzini@redhat.com; 'Ingo Molnar' <mingo@kernel.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



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