2 files changed, 28 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index daed39ba2614..3260ab044996 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -86,6 +86,29 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
          */
         if (c->x86 == 6 && c->x86_model < 15)
                 clear_cpu_cap(c, X86_FEATURE_PAT);
+
+#ifdef CONFIG_KMEMCHECK
+        /*
+         * P4s have a "fast strings" feature which causes single-
+         * stepping REP instructions to only generate a #DB on
+         * cache-line boundaries.
+         *
+         * Ingo Molnar reported a Pentium D (model 6) and a Xeon
+         * (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) {
+                        printk(KERN_INFO "kmemcheck: Disabling fast string operations\n");
+
+                        misc_enable &= ~MSR_IA32_MISC_ENABLE_FAST_STRING;
+                        wrmsrl(MSR_IA32_MISC_ENABLE, misc_enable);
+                }
+        }
+#endif
 }
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 07d60c870ce2..e7a28e6aa4bc 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -45,6 +45,7 @@
 #include <linux/edac.h>
 #endif
 
+#include <asm/kmemcheck.h>
 #include <asm/stacktrace.h>
 #include <asm/processor.h>
 #include <asm/debugreg.h>
@@ -534,6 +535,10 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 
         get_debugreg(condition, 6);
 
+        /* Catch kmemcheck conditions first of all! */
+        if (condition & DR_STEP && kmemcheck_trap(regs))
+                return;
+
         /*
          * The processor cleared BTF, so don't mark that we need it set.
          */