linux-kernel - [PATCH] cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <1776084.Fkt4dJnx8e@kreacher>
Date:   Tue, 14 Jul 2020 20:17:24 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Linux PM <linux-pm@...r.kernel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: [PATCH] cpufreq: intel_pstate: Avoid enabling HWP if EPP is not supported

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Although there are processors supporting hardware-managed P-states
(HWP) without the energy-performance preference (EPP) feature, they
are not expected to be run with HWP enabled (the BIOS should disable
HWP on those systems).  Missing EPP support generally indicates an
incomplete HWP implementation and so it is better to avoid using
HWP on those systems in production.

However, intel_pstate currently enables HWP on such systems, which
is questionable, so prevent it from doing that by making it check
EPP support before enabling HWP and avoid enabling it if EPP is not
supported by the processor at hand.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/cpufreq/intel_pstate.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -2899,7 +2899,12 @@ static int __init intel_pstate_init(void
 	id = x86_match_cpu(hwp_support_ids);
 	if (id) {
 		copy_cpu_funcs(&core_funcs);
-		if (!no_hwp) {
+		/*
+		 * Avoid enabling HWP for processors without EPP support,
+		 * because that means incomplete HWP implementation which is a
+		 * corner case and supporting it is generally problematic.
+		 */
+		if (!no_hwp && boot_cpu_has(X86_FEATURE_HWP_EPP)) {
 			hwp_active++;
 			hwp_mode_bdw = id->driver_data;
 			intel_pstate.attr = hwp_cpufreq_attrs;