From: Prarit Bhargava <prarit@redhat.com>
Subject: Re: [RHEL5 PATCH]: BZ 213050 Fix time skew on Intel Core 2 processors
Date: Tue, 05 Dec 2006 13:12:11 -0500
Bugzilla: 213050
Message-Id: <4575B67B.2020905@redhat.com>
Changelog: Fix time skew on Intel Core 2 processors

New patch ...

P.

On Core2 Intel processors the rdtsc instruction is not serializing.

It's bad and causes "time going backwards" errors on these processors.

Backport of http://marc.theaimsgroup.com/?l=linux-kernel&m=116470988830541&w=2
(and ported into the -xen code)...

Tested by me on mclasen's Dell laptop which exhibited this behaviour.  Further
testing is ongoing.

Fixes BZ 213050.

--- linux-2.6.18.ia64/arch/x86_64/kernel/setup.c.orig	2006-12-05 08:08:37.000000000 -0500
+++ linux-2.6.18.ia64/arch/x86_64/kernel/setup.c	2006-12-05 08:08:44.000000000 -0500
@@ -1011,7 +1011,10 @@ static void __cpuinit init_intel(struct 
 	if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
 	    (c->x86 == 0x6 && c->x86_model >= 0x0e))
 		set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
-	set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
+	if (c->x86 == 15)
+		set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
+	else
+		clear_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
  	c->x86_max_cores = intel_num_cpu_cores(c);
 
 	srat_detect_node();
--- linux-2.6.18.ia64/arch/x86_64/kernel/setup-xen.c.orig	2006-12-05 08:09:11.000000000 -0500
+++ linux-2.6.18.ia64/arch/x86_64/kernel/setup-xen.c	2006-12-05 08:07:54.000000000 -0500
@@ -1259,7 +1259,10 @@ static void __cpuinit init_intel(struct 
 	if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
 	    (c->x86 == 0x6 && c->x86_model >= 0x0e))
 		set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
-	set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
+	if (c->x86 == 15)
+		set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
+	else
+		clear_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
  	c->x86_max_cores = intel_num_cpu_cores(c);
 
 	srat_detect_node();