From: Giovanni Gherdovich <ggherdovich@suse.cz>
Date: Sun, 31 May 2020 20:24:52 +0200
Subject: x86, sched: Bail out of frequency invariance if turbo frequency is
 unknown
Patch-mainline: v5.9-rc1
Git-commit: 51beea8862a3095559862df39554f05042e1195b
References: bsc#1176925

There may be CPUs that support turbo boost but don't declare any turbo
ratio, i.e. their MSR_TURBO_RATIO_LIMIT is all zeroes. In that condition
scale-invariant calculations can't be performed.

Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")
Suggested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Link: https://lkml.kernel.org/r/20200531182453.15254-3-ggherdovich@suse.cz
---
 arch/x86/kernel/smpboot.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -2023,9 +2023,11 @@ out:
 	/*
 	 * Some hypervisors advertise X86_FEATURE_APERFMPERF
 	 * but then fill all MSR's with zeroes.
+	 * Some CPUs have turbo boost but don't declare any turbo ratio
+	 * in MSR_TURBO_RATIO_LIMIT.
 	 */
-	if (!base_freq) {
-		pr_debug("Couldn't determine cpu base frequency, necessary for scale-invariant accounting.\n");
+	if (!base_freq || !turbo_freq) {
+		pr_debug("Couldn't determine cpu base or turbo frequency, necessary for scale-invariant accounting.\n");
 		return false;
 	}