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Rafael J. Wysocki b29c6ef7bb x86 / CPU: Avoid unnecessary IPIs in arch_freq_get_on_cpu() 
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 941f5f0f6e ("x86: CPU: Fix up "cpu MHz"
in /proc/cpuinfo"), but it was not the reason for the revert and it
remains applicable.

Fixes: 4815d3c56d (cpufreq: x86: Make scaling_cur_freq behave more as expected)
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: WANG Chao <chao.wang@ucloud.cn>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2017-11-13 19:42:39 -08:00
..
mcheck Merge branch 'ras-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 13:33:39 -08:00
microcode x86/microcode/intel: Disable late loading on model 79 2017-10-18 15:20:20 +02:00
mtrr License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
.gitignore
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Makefile Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 14:13:48 -08:00
amd.c x86/cpu/AMD: Fix erratum 1076 (CPB bit) 2017-09-15 11:30:53 +02:00
aperfmperf.c x86 / CPU: Avoid unnecessary IPIs in arch_freq_get_on_cpu() 2017-11-13 19:42:39 -08:00
bugs.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
centaur.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
common.c Merge branch 'x86-boot-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 16:32:30 -08:00
cpu.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
cpuid-deps.c x86/cpuid: Replace set/clear_bit32() 2017-11-02 14:56:43 +01:00
cyrix.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
hypervisor.c x86/virt: Add enum for hypervisors to replace x86_hyper 2017-11-10 10:03:12 +01:00
intel.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
intel_cacheinfo.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
intel_rdt.c x86/intel_rdt: Initialize bitmask of shareable resource if CDP enabled 2017-10-21 17:12:21 +02:00
intel_rdt.h Merge branch 'x86-cache-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-11-13 19:05:19 -08:00
intel_rdt_ctrlmondata.c x86/intel_rdt: Fix a silent failure when writing zero value schemata 2017-11-12 09:01:40 +01:00
intel_rdt_monitor.c x86/intel_rdt/cqm: Make integer rmid_limbo_count static 2017-10-05 13:20:32 +02:00
intel_rdt_rdtgroup.c x86/intel_rdt: Fix potential deadlock during resctrl mount 2017-10-21 17:12:22 +02:00
match.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mkcapflags.sh License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mshyperv.c x86/virt: Add enum for hypervisors to replace x86_hyper 2017-11-10 10:03:12 +01:00
perfctr-watchdog.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
powerflags.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
proc.c Revert "x86: CPU: Fix up "cpu MHz" in /proc/cpuinfo" 2017-11-10 11:19:11 -08:00
rdrand.c x86, asm: Use CC_SET()/CC_OUT() and static_cpu_has() in archrandom.h 2016-06-08 12:41:20 -07:00
scattered.c x86/cpu/AMD: Add the Secure Memory Encryption CPU feature 2017-07-18 11:37:59 +02:00
topology.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
transmeta.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
umc.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
vmware.c x86/virt: Add enum for hypervisors to replace x86_hyper 2017-11-10 10:03:12 +01:00