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    SubjectRe: [PATCH 4.4 10/24] x86/fpu: Hard-disable lazy FPU mode
    On Fri, Jun 15, 2018 at 02:23:08PM +0900, Daniel Sangorrin wrote:
    > > -----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

    Minor nit. For kernel commits, the "normal" way we reference them looks
    like this:
    c592b5734706 ("x86/fpu: Remove use_eager_fpu()")
    e63650840e8b ("x86/fpu: Finish excising 'eagerfpu'")

    Which makes it much easier to read and understand. That's what we use
    for the "Fixes:" tag in commits and in other places (text in commit
    messages.)

    To automatically generate that format, you can just do:
    git show -s --abbrev-commit --abbrev=12 --pretty=format:"%h (\"%s\")%n"

    I recommend just setting up an alias for the above line, otherwise it's
    a pain to have to remember how to do it all the time. Here's what I do:
    $ alias gsr='git show -s --abbrev-commit --abbrev=12 --pretty=format:"%h (\"%s\")%n"'
    $ gsr c592b57347069abfc0dcad3b3a302cf882602597
    c592b5734706 ("x86/fpu: Remove use_eager_fpu()")

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

    Should be very simple to backport if you want to. Also I need copies
    for the 4.9.y tree as well if you do so.

    thanks,

    greg k-h

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