lkml.org 
[lkml]   [2011]   [Aug]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRE: [PATCH v2 1/2] x86: Enable fast strings on Intel if BIOS hasn't already
    > -----Original Message-----
    > From: Andy Lutomirski [mailto:luto@MIT.EDU]
    > Sent: Saturday, August 06, 2011 4:43 AM
    > To: x86@kernel.org; linux-kernel@vger.kernel.org
    > Cc: Yu, Fenghua; Matthew Garrett; Len Brown; linux-
    > acpi@vger.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@mit.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.

    I would suggest to remove this printk (and the if () statement) and change KERN_INFO to KERN_WARNING in the following printk.

    > + }
    > +
    > 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



    \
     
     \ /
      Last update: 2011-08-06 21:37    [W:0.148 / U:29.972 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site