linux-kernel - [PATCH AUTOSEL 5.8 07/72] x86, sched: Bail out of frequency invariance if turbo_freq/base

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Date:   Sat,  8 Aug 2020 19:34:36 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Giovanni Gherdovich <ggherdovich@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.8 07/72] x86, sched: Bail out of frequency invariance if turbo_freq/base_freq gives 0

From: Giovanni Gherdovich <ggherdovich@...e.cz>

[ Upstream commit f4291df103315a696f0b8c4f45ca8ae773c17441 ]

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

Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")
Signed-off-by: Giovanni Gherdovich <ggherdovich@...e.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Link: https://lkml.kernel.org/r/20200531182453.15254-4-ggherdovich@suse.cz
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kernel/smpboot.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 20e1cea262e4b..518ac6bf752e0 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/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;
 }
 
-- 
2.25.1