From: "mike.travis@hpe.com" <mike.travis@hpe.com>
Subject: x86/tsc: Skip TSC test and error messages if already unstable
Git-commit: 9514ececa52e9f1436e7682e98c852d1338b699f
Patch-mainline: v4.15-rc1
References: bsc#1082579
Acked-by: Jiri Bohac <jbohac@suse.cz>

If the TSC has already been determined to be unstable, then checking
TSC ADJUST values is a waste of time and generates unnecessary error
messages.

Signed-off-by: Mike Travis <mike.travis@hpe.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Reviewed-by: Russ Anderson <russ.anderson@hpe.com>
Reviewed-by: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Andrew Banman <andrew.banman@hpe.com>
Cc: Bin Gao <bin.gao@linux.intel.com>
Link: https://lkml.kernel.org/r/20171012163202.060777495@stormcage.americas.sgi.com

---
 arch/x86/kernel/tsc_sync.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/arch/x86/kernel/tsc_sync.c
+++ b/arch/x86/kernel/tsc_sync.c
@@ -52,6 +52,10 @@ void tsc_verify_tsc_adjust(bool resume)
 	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
 		return;
 
+	/* Skip unnecessary error messages if TSC already unstable */
+	if (check_tsc_unstable())
+		return;
+
 	/* Rate limit the MSR check */
 	if (!resume && time_before(jiffies, adj->nextcheck))
 		return;
@@ -120,6 +124,10 @@ bool __init tsc_store_and_check_tsc_adju
 	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
 		return false;
 
+	/* Skip unnecessary error messages if TSC already unstable */
+	if (check_tsc_unstable())
+		return false;
+
 	rdmsrl(MSR_IA32_TSC_ADJUST, bootval);
 	cur->bootval = bootval;
 	cur->nextcheck = jiffies + HZ;