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>] [thread-next>] [day] [month] [year] [list]
Date:	Fri, 26 Feb 2016 17:38 +0100
From:	Thomas Renninger <trenn@...e.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	lenb@...nel.org, rjw@...ysocki.net,
	Thomas Renninger <trenn@...e.com>, x86@...nel.org
Subject: [PATCH] Do not modify MSR_IA32_ENERGY_PERF_BIAS in kernel

The assumption that BIOSes never want to have this register being set to
full performance (zero) is wrong.

While wrongly overruling this BIOS setting and set it from performance
to normal did not hurt that much, because nobody really knew the effects inside
Intel processors.

But with Broadwell-EP processor (E5-2687W v4) the CPU will not enter turbo modes
if this value is not set to performance.

So switch logic to tell the user in a friendly way (info) that the CPU is in
performance mode and how to switch via userspace if this is not intended.

But otherwise trust that the BIOS has set the correct value here and do not
blindly overrule.

How this has been found: SLE11 had this patch, SLE12 it slipped through.
It took quite some time to nail down that this patch missing is the reason
for not entering turbo modes with this specific processor.

Signed-off-by: Thomas Renninger <trenn@...e.com>

--- a/arch/x86/kernel/cpu/intel.c	2016-02-26 17:19:55.731042972 +0100
+++ b/arch/x86/kernel/cpu/intel.c	2016-02-26 17:20:48.598020581 +0100
@@ -377,8 +377,12 @@ static void init_intel_energy_perf(struc
 	u64 epb;
 
 	/*
-	 * Initialize MSR_IA32_ENERGY_PERF_BIAS if not already initialized.
-	 * (x86_energy_perf_policy(8) is available to change it at run-time.)
+	 * On server platforms energy bias typically is set to
+	 * performance on purpose.
+	 * On other platforms it may happen that MSR_IA32_ENERGY_PERF_BIAS
+	 * did not get initialized properly by BIOS.
+	 * Best is to to keep BIOS settings and give the user a hint whether
+	 * to change it via cpupower-set(8) userspace tool at runtime.
 	 */
 	if (!cpu_has(c, X86_FEATURE_EPB))
 		return;
@@ -387,10 +391,8 @@ static void init_intel_energy_perf(struc
 	if ((epb & 0xF) != ENERGY_PERF_BIAS_PERFORMANCE)
 		return;
 
-	pr_warn_once("ENERGY_PERF_BIAS: Set to 'normal', was 'performance'\n");
-	pr_warn_once("ENERGY_PERF_BIAS: View and update with x86_energy_perf_policy(8)\n");
-	epb = (epb & ~0xF) | ENERGY_PERF_BIAS_NORMAL;
-	wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
+	pr_info_once("ENERGY_PERF_BIAS is set to 'performance'\n");
+	pr_info_once("ENERGY_PERF_BIAS: Update with cpupower-set(8)\n");
 }
 
 static void intel_bsp_resume(struct cpuinfo_x86 *c)

Powered by blists - more mailing lists