x86, mem, intel: Initialize Enhanced REP MOVSB/STOSB

If kernel intends to use enhanced REP MOVSB/STOSB, it must ensure
IA32_MISC_ENABLE.Fast_String_Enable (bit 0) is set and CPUID.(EAX=07H, ECX=0H):
EBX[bit 9] also reports 1.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1305671358-14478-3-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 15 insertions, 4 deletions

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index df86bc8c859d..fc73a34ba8c9 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -29,10 +29,10 @@
 
 static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
 {
+        u64 misc_enable;
+
         /* Unmask CPUID levels if masked: */
         if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
-                u64 misc_enable;
-
                 rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
 
                 if (misc_enable & MSR_IA32_MISC_ENABLE_LIMIT_CPUID) {
@@ -118,8 +118,6 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
          * (model 2) with the same problem.
          */
         if (c->x86 == 15) {
-                u64 misc_enable;
-
                 rdmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
 
                 if (misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING) {
@@ -130,6 +128,19 @@ 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 (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
+                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);
+                        setup_clear_cpu_cap(X86_FEATURE_ERMS);
+                }
+        }
 }
 
 #ifdef CONFIG_X86_32