x86: do not enable TSC notifier if we don't need it

Impact: crash on non-TSC-equipped CPUs

Don't enable the TSC notifier if we *either*:

1. don't have a CPU, or
2. have a CPU with constant TSC.

In either of those cases, the notifier is either damaging (1) or useless(2).

From: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 46af7167673..9bed5cae4bd 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -325,6 +325,10 @@ static struct notifier_block time_cpufreq_notifier_block = {
 
 static int __init cpufreq_tsc(void)
 {
+        if (!cpu_has_tsc)
+                return 0;
+        if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
+                return 0;
         cpufreq_register_notifier(&time_cpufreq_notifier_block,
                                 CPUFREQ_TRANSITION_NOTIFIER);
         return 0;