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


    > -----Original Message-----
    > From: Andy Lutomirski [mailto:luto@MIT.EDU]
    > Sent: Wednesday, August 03, 2011 8:47 AM
    > To: x86@kernel.org; linux-kernel@vger.kernel.org
    > Cc: Yu, Fenghua; Andy Lutomirski
    > Subject: [PATCH 1/2] x86: Enable fast strings on Intel if BIOS hasn't
    > already
    >
    > I have two Sandy Bridge systems and neither one enables fast strings
    > in BIOS. I can't find anything in the manual that says that only
    > BIOS should enable or disable the feature, so try to enable it at
    > bootup.
    >
    > Signed-off-by: Andy Lutomirski <luto@mit.edu>
    > ---
    > arch/x86/kernel/cpu/intel.c | 17 +++++++++++++++--
    > 1 files changed, 15 insertions(+), 2 deletions(-)
    >
    > diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
    > index ed6086e..6b20fef 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)) {
    > @@ -118,10 +119,11 @@ 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;
    > + printk(KERN_INFO "kmemcheck: Disabling fast string
    > operations\n");

    Please don't move this printk() here. Keep it in the original place. If fast string bit is 0 already, we don't need to print the info.

    >
    > + 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");
    >
    > misc_enable &= ~MSR_IA32_MISC_ENABLE_FAST_STRING;
    > wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
    > @@ -135,6 +137,17 @@ static void __cpuinit early_init_intel(struct
    > cpuinfo_x86 *c)

    You also need to change the comment right before this code. With your patch, the comment is out-of-date.

    > */
    > 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;
    > + wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
    > + printk(KERN_INFO "Enabled fast string operations\n");
    > +
    > + /* 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_INFO "Disabled fast string
    > operations\n");
    > setup_clear_cpu_cap(X86_FEATURE_REP_GOOD);
    > --
    > 1.7.6



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