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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
        Giovanni Gherdovich <ggherdovich@suse.cz>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.8 010/464] x86, sched: Bail out of frequency invariance if turbo frequency is unknown
Date:   Mon, 17 Aug 2020 17:09:23 +0200
Message-Id: <20200817143834.247565223@linuxfoundation.org>
In-Reply-To: <20200817143833.737102804@linuxfoundation.org>
References: <20200817143833.737102804@linuxfoundation.org>
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From: Giovanni Gherdovich <ggherdovich@suse.cz>

[ Upstream commit 51beea8862a3095559862df39554f05042e1195b ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kernel/smpboot.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 18d292fc466cb..20e1cea262e4b 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -2002,9 +2002,11 @@ static bool intel_set_max_freq_ratio(void)
 	/*
 	 * 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;
 	}
 
-- 
2.25.1