x86, sched: Bail out of frequency invariance if turbo_freq/base_freq gives 0

Be defensive against the case where the processor reports a base_freq
larger than turbo_freq (the ratio would be zero).

Fixes: 1567c3e3 ("x86, sched: Add support for frequency invariance")
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>
Link: https://lkml.kernel.org/r/20200531182453.15254-4-ggherdovich@suse.cz

arch/x86/kernel/smpboot.c

@@ -1977,6 +1977,7 @@ static bool core_set_max_freq_ratio(u64 *base_freq, u64 *turbo_freq)
 static bool intel_set_max_freq_ratio(void)
 {
 	u64 base_freq, turbo_freq;
+	u64 turbo_ratio;
 
 	if (slv_set_max_freq_ratio(&base_freq, &turbo_freq))
 		goto out;
@@ -2010,9 +2011,15 @@ static bool intel_set_max_freq_ratio(void)
 		return false;
 	}
 
-	arch_turbo_freq_ratio = div_u64(turbo_freq * SCHED_CAPACITY_SCALE,
-					base_freq);
+	turbo_ratio = div_u64(turbo_freq * SCHED_CAPACITY_SCALE, base_freq);
+	if (!turbo_ratio) {
+		pr_debug("Non-zero turbo and base frequencies led to a 0 ratio.\n");
+		return false;
+	}
+
+	arch_turbo_freq_ratio = turbo_ratio;
 	arch_set_max_freq_ratio(turbo_disabled());
+
 	return true;
 }