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

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Message-Id: <1235223364-2097-2-git-send-email-vegard.nossum@gmail.com>
Date:	Sat, 21 Feb 2009 14:36:01 +0100
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:	Ingo Molnar <mingo@...e.hu>, Pekka Enberg <penberg@...helsinki.fi>
Subject: [PATCH] kmemcheck: disable fast string operations on P4 CPUs

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

Signed-off-by: Vegard Nossum <vegard.nossum@...il.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

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