linux-kernel - [PATCH] cpufreq: intel_pstate: Fix Invalid EPB setting

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Message-Id: <20191031192620.23482-1-srinivas.pandruvada@linux.intel.com>
Date:   Thu, 31 Oct 2019 12:26:20 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     rjw@...ysocki.net, viresh.kumar@...aro.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, cai@....pw
Subject: [PATCH] cpufreq: intel_pstate: Fix Invalid EPB setting

The max value of EPB can be only be 0x0F. Setting more than that results
in "unchecked MSR access error". During CPU offline via cpufreq stop_cpu()
callback, this error condition is triggered in the function
intel_pstate_hwp_force_min_perf().

Instead, EPB corresponding to preference to maximize energy saving (0x0F),
can be set. But this will conflict with the save/restore done in
arch/x86/kernel/cpu/intel_epb.c. Based on the test, if 0x0F is set in the
function intel_pstate_hwp_force_min_perf(), this gets restored during next
CPU online operation. This is not desired.

Hence don't set EPB in the offline path in this driver and let the
processing in intel_epb.c handle EPB.

Fixes: af3b7379e2d70 ("cpufreq: intel_pstate: Force HWP min perf before offline")
Reported-by: Qian Cai <cai@....pw>
Cc: 5.0+ <stable@...r.kernel.org> # 5.0+
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
---
 drivers/cpufreq/intel_pstate.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 53a51c169451..8ab31702cf6a 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -847,11 +847,9 @@ static void intel_pstate_hwp_force_min_perf(int cpu)
 	value |= HWP_MAX_PERF(min_perf);
 	value |= HWP_MIN_PERF(min_perf);

-	/* Set EPP/EPB to min */
+	/* Set EPP to min */
 	if (boot_cpu_has(X86_FEATURE_HWP_EPP))
 		value |= HWP_ENERGY_PERF_PREFERENCE(HWP_EPP_POWERSAVE);
-	else
-		intel_pstate_set_epb(cpu, HWP_EPP_BALANCE_POWERSAVE);

 	wrmsrl_on_cpu(cpu, MSR_HWP_REQUEST, value);
 }
-- 
2.17.2