2 files changed, 28 insertions, 12 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 1bbcaa8982b6..dc6b06f67fca 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2267,6 +2267,13 @@ and is between 256 and 4096 characters. It is defined in the file
                         Format:
                         <io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq>
 
+        tsc=            Disable clocksource-must-verify flag for TSC.
+                        Format: <string>
+                        [x86] reliable: mark tsc clocksource as reliable, this
+                        disables clocksource verification at runtime.
+                        Used to enable high-resolution timer mode on older
+                        hardware, and in virtualized environment.
+
         turbografx.map[2|3]=    [HW,JOY]
                         TurboGraFX parallel port interface
                         Format:
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 6dbf0bcb44a8..ee01cd96b5e1 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -32,6 +32,7 @@ static int tsc_unstable;
    erroneous rdtsc usage on !cpu_has_tsc processors */
 static int tsc_disabled = -1;
 
+static int tsc_clocksource_reliable;
 /*
  * Scheduler clock - returns current time in nanosec units.
  */
@@ -99,6 +100,15 @@ int __init notsc_setup(char *str)
 
 __setup("notsc", notsc_setup);
 
+static int __init tsc_setup(char *str)
+{
+        if (!strcmp(str, "reliable"))
+                tsc_clocksource_reliable = 1;
+        return 1;
+}
+
+__setup("tsc=", tsc_setup);
+
 #define MAX_RETRIES     5
 #define SMI_TRESHOLD    50000
 
@@ -738,24 +748,21 @@ static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
         {}
 };
 
-/*
- * Geode_LX - the OLPC CPU has a possibly a very reliable TSC
- */
+static void __init check_system_tsc_reliable(void)
+{
 #ifdef CONFIG_MGEODE_LX
-/* RTSC counts during suspend */
+        /* RTSC counts during suspend */
 #define RTSC_SUSP 0x100
-
-static void __init check_geode_tsc_reliable(void)
-{
         unsigned long res_low, res_high;
 
         rdmsr_safe(MSR_GEODE_BUSCONT_CONF0, &res_low, &res_high);
+        /* Geode_LX - the OLPC CPU has a possibly a very reliable TSC */
         if (res_low & RTSC_SUSP)
-                clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
-}
-#else
-static inline void check_geode_tsc_reliable(void) { }
+                tsc_clocksource_reliable = 1;
 #endif
+        if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE))
+                tsc_clocksource_reliable = 1;
+}
 
 /*
  * Make an educated guess if the TSC is trustworthy and synchronized
@@ -790,6 +797,8 @@ static void __init init_tsc_clocksource(void)
 {
         clocksource_tsc.mult = clocksource_khz2mult(tsc_khz,
                         clocksource_tsc.shift);
+        if (tsc_clocksource_reliable)
+                clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
         /* lower the rating if we already know its unstable: */
         if (check_tsc_unstable()) {
                 clocksource_tsc.rating = 0;
@@ -850,7 +859,7 @@ void __init tsc_init(void)
         if (unsynchronized_tsc())
                 mark_tsc_unstable("TSCs unsynchronized");
 
-        check_geode_tsc_reliable();
+        check_system_tsc_reliable();
         init_tsc_clocksource();
 }