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From:   Giovanni Gherdovich <ggherdovich@suse.cz>
To:     Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@suse.de>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>
Cc:     x86@kernel.org, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
        Giovanni Gherdovich <ggherdovich@suse.cz>
Subject: [PATCH v2 3/3] x86, sched: Bail out of frequency invariance if turbo_freq/base_freq gives 0
Date:   Sun, 31 May 2020 20:24:53 +0200
Message-Id: <20200531182453.15254-4-ggherdovich@suse.cz>
In-Reply-To: <20200531182453.15254-1-ggherdovich@suse.cz>
References: <20200531182453.15254-1-ggherdovich@suse.cz>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance")
---
 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 fe154c8226ba..f619007f46cf 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1976,6 +1976,7 @@ 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;
@@ -2009,9 +2010,15 @@ 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;
 }
 
-- 
2.16.4