From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:41678 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752537AbeAFIpz (ORCPT ); Sat, 6 Jan 2018 03:45:55 -0500 Subject: Patch "x86 / CPU: Avoid unnecessary IPIs in arch_freq_get_on_cpu()" has been added to the 4.14-stable tree To: rafael.j.wysocki@intel.com, chao.wang@ucloud.cn, gregkh@linuxfoundation.org, torvalds@linux-foundation.org Cc: , From: Date: Sat, 06 Jan 2018 09:45:50 +0100 Message-ID: <151522835019252@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled x86 / CPU: Avoid unnecessary IPIs in arch_freq_get_on_cpu() to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-cpu-avoid-unnecessary-ipis-in-arch_freq_get_on_cpu.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From b29c6ef7bb1257853c1e31616d84f55e561cf631 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Mon, 13 Nov 2017 02:15:39 +0100 Subject: x86 / CPU: Avoid unnecessary IPIs in arch_freq_get_on_cpu() From: Rafael J. Wysocki commit b29c6ef7bb1257853c1e31616d84f55e561cf631 upstream. Even though aperfmperf_snapshot_khz() caches the samples.khz value to return if called again in a sufficiently short time, its caller, arch_freq_get_on_cpu(), still uses smp_call_function_single() to run it which may allow user space to trigger an IPI storm by reading from the scaling_cur_freq cpufreq sysfs file in a tight loop. To avoid that, move the decision on whether or not to return the cached samples.khz value to arch_freq_get_on_cpu(). This change was part of commit 941f5f0f6ef5 ("x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo"), but it was not the reason for the revert and it remains applicable. Fixes: 4815d3c56d1e (cpufreq: x86: Make scaling_cur_freq behave more as expected) Signed-off-by: Rafael J. Wysocki Reviewed-by: WANG Chao Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/aperfmperf.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) --- a/arch/x86/kernel/cpu/aperfmperf.c +++ b/arch/x86/kernel/cpu/aperfmperf.c @@ -42,10 +42,6 @@ static void aperfmperf_snapshot_khz(void s64 time_delta = ktime_ms_delta(now, s->time); unsigned long flags; - /* Don't bother re-computing within the cache threshold time. */ - if (time_delta < APERFMPERF_CACHE_THRESHOLD_MS) - return; - local_irq_save(flags); rdmsrl(MSR_IA32_APERF, aperf); rdmsrl(MSR_IA32_MPERF, mperf); @@ -74,6 +70,7 @@ static void aperfmperf_snapshot_khz(void unsigned int arch_freq_get_on_cpu(int cpu) { + s64 time_delta; unsigned int khz; if (!cpu_khz) @@ -82,6 +79,12 @@ unsigned int arch_freq_get_on_cpu(int cp if (!static_cpu_has(X86_FEATURE_APERFMPERF)) return 0; + /* Don't bother re-computing within the cache threshold time. */ + time_delta = ktime_ms_delta(ktime_get(), per_cpu(samples.time, cpu)); + khz = per_cpu(samples.khz, cpu); + if (khz && time_delta < APERFMPERF_CACHE_THRESHOLD_MS) + return khz; + smp_call_function_single(cpu, aperfmperf_snapshot_khz, NULL, 1); khz = per_cpu(samples.khz, cpu); if (khz) Patches currently in stable-queue which might be from rafael.j.wysocki@intel.com are queue-4.14/x86-cpu-always-show-current-cpu-frequency-in-proc-cpuinfo.patch queue-4.14/x86-cpu-avoid-unnecessary-ipis-in-arch_freq_get_on_cpu.patch