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Subject[PATCH 1/2] x86: Enable fast strings on Intel if BIOS hasn't already
Date
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");

+ 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)
*/
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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