[PATCH] kmemcheck: disable fast string operations on P4 CPUs

Vegard Nossum
2009-02-21T13:36:40Z

This patch may allow us to remove the REP emulation code from
kmemcheck.

Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
---
arch/x86/kernel/cpu/intel.c | 23 +++++++++++++++++++++++
1 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 1f137a8..65e9717 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -75,6 +75,29 @@ 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
--
1.6.0.6