-----Original Message----- From: 'Greg Kroah-Hartman' [mailto:gregkh@linuxfoundation.org] Sent: Friday, June 15, 2018 4:06 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 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()")
Thanks a lot for the detailed explanation.
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.
OK, I will do it after the OSS Japan next week if you don't mind. I also want to run some tests for the FPU and try different boot parameter combinations (e.g. no387, nofxsr etc) to check I didn't break anything.
Thanks, Daniel
thanks,
greg k-h