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

From: Andrew Lutomirski
Date: Tue Aug 09 2011 - 11:13:08 EST


On Tue, Aug 9, 2011 at 11:00 AM, Ingo Molnar <mingo@xxxxxxx> wrote:
>
> * Yu, Fenghua <fenghua.yu@xxxxxxxxx> wrote:
>
>> > -----Original Message-----
>> > From: amluto@xxxxxxxxx [mailto:amluto@xxxxxxxxx] On Behalf Of Andrew
>> > Lutomirski
>> > Sent: Saturday, August 06, 2011 4:32 PM
>> > To: Yu, Fenghua
>> > Cc: x86@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Matthew Garrett; Len
>> > Brown; linux-acpi@xxxxxxxxxxxxxxx; 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@xxxxxxxxx>
>> > wrote:
>> > >> -----Original Message-----
>> > >> From: Andy Lutomirski [mailto:luto@xxxxxxx]
>> > >> Sent: Saturday, August 06, 2011 4:43 AM
>> > >> To: x86@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
>> > >> Cc: Yu, Fenghua; Matthew Garrett; Len Brown; linux-
>> > >> acpi@xxxxxxxxxxxxxxx; 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@xxxxxxx>
>> > >> ---
>> > >>  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.

Already there in v3.

--Andy

>
> Thanks,
>
>        Ingo
>
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