linux-kernel - Re: [PATCH v2 1/2] x86: Enable fast strings on Intel if BIOS hasn't already

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Date:	Tue, 9 Aug 2011 17:00:35 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>
Cc:	Andrew Lutomirski <luto@....edu>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Len Brown <lenb@...nel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] x86: Enable fast strings on Intel if BIOS hasn't
 already


* Yu, Fenghua <fenghua.yu@...el.com> wrote:

> > -----Original Message-----
> > From: amluto@...il.com [mailto:amluto@...il.com] On Behalf Of Andrew
> > Lutomirski
> > Sent: Saturday, August 06, 2011 4:32 PM
> > To: Yu, Fenghua
> > Cc: x86@...nel.org; linux-kernel@...r.kernel.org; Matthew Garrett; Len
> > Brown; linux-acpi@...r.kernel.org; Ingo Molnar
> > Subject: Re: [PATCH v2 1/2] x86: Enable fast strings on Intel if BIOS
> > hasn't already
> > 
> > On Sat, Aug 6, 2011 at 3:33 PM, Yu, Fenghua <fenghua.yu@...el.com>
> > wrote:
> > >> -----Original Message-----
> > >> From: Andy Lutomirski [mailto:luto@....EDU]
> > >> Sent: Saturday, August 06, 2011 4:43 AM
> > >> To: x86@...nel.org; linux-kernel@...r.kernel.org
> > >> Cc: Yu, Fenghua; Matthew Garrett; Len Brown; linux-
> > >> acpi@...r.kernel.org; Ingo Molnar; Andy Lutomirski
> > >> Subject: [PATCH v2 1/2] x86: Enable fast strings on Intel if BIOS
> > >> hasn't already
> > >>
> > >> Intel SDM volume 3A, 8.4.2 says:
> > >>
> > >>   Software can disable fast-string operation by clearing the
> > >>   fast-string-enable bit (bit 0) of IA32_MISC_ENABLE MSR.
> > >>   However, Intel recomments that system software always enable
> > >>   fast-string operation.
> > >>
> > >> The Intel DQ67SW board (with latest BIOS) disables fast string
> > >> operations if TXT is enabled.  A Lenovo X220 disables it regardless
> > >> of TXT setting.  I doubt I'm the only person with a dumb BIOS like
> > >> this.
> > >>
> > >> Signed-off-by: Andy Lutomirski <luto@....edu>
> > >> ---
> > >>  arch/x86/kernel/cpu/intel.c |   25 ++++++++++++++++++++++---
> > >>  1 files changed, 22 insertions(+), 3 deletions(-)
> > >>
> > >> diff --git a/arch/x86/kernel/cpu/intel.c
> > b/arch/x86/kernel/cpu/intel.c
> > >> index ed6086e..c80ab41 100644
> > >> --- a/arch/x86/kernel/cpu/intel.c
> > >> +++ b/arch/x86/kernel/cpu/intel.c
> > >> @@ -30,6 +30,7 @@
> > >>  static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
> > >>  {
> > >>       u64 misc_enable;
> > >> +     bool allow_fast_string = true;
> > >>
> > >>       /* Unmask CPUID levels if masked: */
> > >>       if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
> > >> @@ -118,8 +119,9 @@ static void __cpuinit early_init_intel(struct
> > >> cpuinfo_x86 *c)
> > >>        * (model 2) with the same problem.
> > >>        */
> > >>       if (c->x86 == 15) {
> > >> -             rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
> > >> +             allow_fast_string = false;
> > >>
> > >> +             rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
> > >>               if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING) {
> > >>                       printk(KERN_INFO "kmemcheck: Disabling fast
> > string
> > >> operations\n");
> > >>
> > >> @@ -130,11 +132,28 @@ static void __cpuinit early_init_intel(struct
> > >> cpuinfo_x86 *c)
> > >>  #endif
> > >>
> > >>       /*
> > >> -      * If fast string is not enabled in IA32_MISC_ENABLE for any
> > >> reason,
> > >> -      * clear the fast string and enhanced fast string CPU
> > >> capabilities.
> > >> +      * If BIOS didn't enable fast string operation, try to enable
> > >> +      * it ourselves.  If that fails, then clear the fast string
> > >> +      * and enhanced fast string CPU capabilities.
> > >>        */
> > >>       if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
> > >>               rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
> > >> +
> > >> +             if (allow_fast_string &&
> > >> +                 !(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING))
> > {
> > >> +                     misc_enable |=
> > MSR_IA32_MISC_ENABLE_FAST_STRING;
> > >> +                     wrmsr_safe(MSR_IA32_MISC_ENABLE,
> > (u32)misc_enable,
> > >> +                                (u32)(misc_enable >> 32));
> > >> +
> > >> +                     /* Re-read to make sure it stuck. */
> > >> +                     rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
> > >> +
> > >> +                     if (misc_enable &
> > MSR_IA32_MISC_ENABLE_FAST_STRING)
> > >> +                             printk(KERN_WARNING FW_WARN "CPU #%d:
> > "
> > >> +
> >  "IA32_MISC_ENABLE.FAST_STRING_ENABLE "
> > >> +                                    "was not set", c->cpu_index);
> > > This printk is redundant because the same info is dumped in the below
> > printk. Plus it's not firmware's issue if we can not set fast string
> > bit 0 in MISC_ENABLE register. So I don't think FW_WARN is right.
> > 
> > Huh?  This is the success path -- the patch prints the warning if
> > flipping the bit worked...
> 
> Ok. I see.
> 
> Still I would suggest to remove this printk. This info will be 
> printed on every single CPU if BIOS doesn't enable fast string. 

just do printk_once(). We want to inform the user that something's 
going on.

Thanks,

	Ingo
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