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linux/Documentation/ABI/testing/sysfs-devices-system-cpu
Linus Torvalds fa4bff1650 Merge branch 'x86-mds-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 
Pull x86 MDS mitigations from Thomas Gleixner:
 "Microarchitectural Data Sampling (MDS) is a hardware vulnerability
  which allows unprivileged speculative access to data which is
  available in various CPU internal buffers. This new set of misfeatures
  has the following CVEs assigned:

     CVE-2018-12126  MSBDS  Microarchitectural Store Buffer Data Sampling
     CVE-2018-12130  MFBDS  Microarchitectural Fill Buffer Data Sampling
     CVE-2018-12127  MLPDS  Microarchitectural Load Port Data Sampling
     CVE-2019-11091  MDSUM  Microarchitectural Data Sampling Uncacheable Memory

  MDS attacks target microarchitectural buffers which speculatively
  forward data under certain conditions. Disclosure gadgets can expose
  this data via cache side channels.

  Contrary to other speculation based vulnerabilities the MDS
  vulnerability does not allow the attacker to control the memory target
  address. As a consequence the attacks are purely sampling based, but
  as demonstrated with the TLBleed attack samples can be postprocessed
  successfully.

  The mitigation is to flush the microarchitectural buffers on return to
  user space and before entering a VM. It's bolted on the VERW
  instruction and requires a microcode update. As some of the attacks
  exploit data structures shared between hyperthreads, full protection
  requires to disable hyperthreading. The kernel does not do that by
  default to avoid breaking unattended updates.

  The mitigation set comes with documentation for administrators and a
  deeper technical view"

* 'x86-mds-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits)
  x86/speculation/mds: Fix documentation typo
  Documentation: Correct the possible MDS sysfs values
  x86/mds: Add MDSUM variant to the MDS documentation
  x86/speculation/mds: Add 'mitigations=' support for MDS
  x86/speculation/mds: Print SMT vulnerable on MSBDS with mitigations off
  x86/speculation/mds: Fix comment
  x86/speculation/mds: Add SMT warning message
  x86/speculation: Move arch_smt_update() call to after mitigation decisions
  x86/speculation/mds: Add mds=full,nosmt cmdline option
  Documentation: Add MDS vulnerability documentation
  Documentation: Move L1TF to separate directory
  x86/speculation/mds: Add mitigation mode VMWERV
  x86/speculation/mds: Add sysfs reporting for MDS
  x86/speculation/mds: Add mitigation control for MDS
  x86/speculation/mds: Conditionally clear CPU buffers on idle entry
  x86/kvm/vmx: Add MDS protection when L1D Flush is not active
  x86/speculation/mds: Clear CPU buffers on exit to user
  x86/speculation/mds: Add mds_clear_cpu_buffers()
  x86/kvm: Expose X86_FEATURE_MD_CLEAR to guests
  x86/speculation/mds: Add BUG_MSBDS_ONLY
  ...
2019-05-14 07:57:29 -07:00

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What: /sys/devices/system/cpu/
Date: pre-git history
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description:
A collection of both global and individual CPU attributes
Individual CPU attributes are contained in subdirectories
named by the kernel's logical CPU number, e.g.:
/sys/devices/system/cpu/cpu#/
What: /sys/devices/system/cpu/kernel_max
/sys/devices/system/cpu/offline
/sys/devices/system/cpu/online
/sys/devices/system/cpu/possible
/sys/devices/system/cpu/present
Date: December 2008
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: CPU topology files that describe kernel limits related to
hotplug. Briefly:
kernel_max: the maximum cpu index allowed by the kernel
configuration.
offline: cpus that are not online because they have been
HOTPLUGGED off or exceed the limit of cpus allowed by the
kernel configuration (kernel_max above).
online: cpus that are online and being scheduled.
possible: cpus that have been allocated resources and can be
brought online if they are present.
present: cpus that have been identified as being present in
the system.
See Documentation/cputopology.txt for more information.
What: /sys/devices/system/cpu/probe
/sys/devices/system/cpu/release
Date: November 2009
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Dynamic addition and removal of CPU's. This is not hotplug
removal, this is meant complete removal/addition of the CPU
from the system.
probe: writes to this file will dynamically add a CPU to the
system. Information written to the file to add CPU's is
architecture specific.
release: writes to this file dynamically remove a CPU from
the system. Information writtento the file to remove CPU's
is architecture specific.
What: /sys/devices/system/cpu/cpu#/node
Date: October 2009
Contact: Linux memory management mailing list <linux-mm@kvack.org>
Description: Discover NUMA node a CPU belongs to
When CONFIG_NUMA is enabled, a symbolic link that points
to the corresponding NUMA node directory.
For example, the following symlink is created for cpu42
in NUMA node 2:
/sys/devices/system/cpu/cpu42/node2 -> ../../node/node2
What: /sys/devices/system/cpu/cpu#/topology/core_id
/sys/devices/system/cpu/cpu#/topology/core_siblings
/sys/devices/system/cpu/cpu#/topology/core_siblings_list
/sys/devices/system/cpu/cpu#/topology/physical_package_id
/sys/devices/system/cpu/cpu#/topology/thread_siblings
/sys/devices/system/cpu/cpu#/topology/thread_siblings_list
Date: December 2008
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: CPU topology files that describe a logical CPU's relationship
to other cores and threads in the same physical package.
One cpu# directory is created per logical CPU in the system,
e.g. /sys/devices/system/cpu/cpu42/.
Briefly, the files above are:
core_id: the CPU core ID of cpu#. Typically it is the
hardware platform's identifier (rather than the kernel's).
The actual value is architecture and platform dependent.
core_siblings: internal kernel map of cpu#'s hardware threads
within the same physical_package_id.
core_siblings_list: human-readable list of the logical CPU
numbers within the same physical_package_id as cpu#.
physical_package_id: physical package id of cpu#. Typically
corresponds to a physical socket number, but the actual value
is architecture and platform dependent.
thread_siblings: internel kernel map of cpu#'s hardware
threads within the same core as cpu#
thread_siblings_list: human-readable list of cpu#'s hardware
threads within the same core as cpu#
See Documentation/cputopology.txt for more information.
What: /sys/devices/system/cpu/cpuidle/current_driver
/sys/devices/system/cpu/cpuidle/current_governer_ro
/sys/devices/system/cpu/cpuidle/available_governors
/sys/devices/system/cpu/cpuidle/current_governor
Date: September 2007
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Discover cpuidle policy and mechanism
Various CPUs today support multiple idle levels that are
differentiated by varying exit latencies and power
consumption during idle.
Idle policy (governor) is differentiated from idle mechanism
(driver)
current_driver: (RO) displays current idle mechanism
current_governor_ro: (RO) displays current idle policy
With the cpuidle_sysfs_switch boot option enabled (meant for
developer testing), the following three attributes are visible
instead:
current_driver: same as described above
available_governors: (RO) displays a space separated list of
available governors
current_governor: (RW) displays current idle policy. Users can
switch the governor at runtime by writing to this file.
See files in Documentation/cpuidle/ for more information.
What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/name
/sys/devices/system/cpu/cpuX/cpuidle/stateN/latency
/sys/devices/system/cpu/cpuX/cpuidle/stateN/power
/sys/devices/system/cpu/cpuX/cpuidle/stateN/time
/sys/devices/system/cpu/cpuX/cpuidle/stateN/usage
/sys/devices/system/cpu/cpuX/cpuidle/stateN/above
/sys/devices/system/cpu/cpuX/cpuidle/stateN/below
Date: September 2007
KernelVersion: v2.6.24
Contact: Linux power management list <linux-pm@vger.kernel.org>
Description:
The directory /sys/devices/system/cpu/cpuX/cpuidle contains per
logical CPU specific cpuidle information for each online cpu X.
The processor idle states which are available for use have the
following attributes:
name: (RO) Name of the idle state (string).
latency: (RO) The latency to exit out of this idle state (in
microseconds).
power: (RO) The power consumed while in this idle state (in
milliwatts).
time: (RO) The total time spent in this idle state (in microseconds).
usage: (RO) Number of times this state was entered (a count).
above: (RO) Number of times this state was entered, but the
observed CPU idle duration was too short for it (a count).
below: (RO) Number of times this state was entered, but the
observed CPU idle duration was too long for it (a count).
What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/desc
Date: February 2008
KernelVersion: v2.6.25
Contact: Linux power management list <linux-pm@vger.kernel.org>
Description:
(RO) A small description about the idle state (string).
What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/disable
Date: March 2012
KernelVersion: v3.10
Contact: Linux power management list <linux-pm@vger.kernel.org>
Description:
(RW) Option to disable this idle state (bool). The behavior and
the effect of the disable variable depends on the implementation
of a particular governor. In the ladder governor, for example,
it is not coherent, i.e. if one is disabling a light state, then
all deeper states are disabled as well, but the disable variable
does not reflect it. Likewise, if one enables a deep state but a
lighter state still is disabled, then this has no effect.
What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/residency
Date: March 2014
KernelVersion: v3.15
Contact: Linux power management list <linux-pm@vger.kernel.org>
Description:
(RO) Display the target residency i.e. the minimum amount of
time (in microseconds) this cpu should spend in this idle state
to make the transition worth the effort.
What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/
Date: March 2018
KernelVersion: v4.17
Contact: Linux power management list <linux-pm@vger.kernel.org>
Description:
Idle state usage statistics related to suspend-to-idle.
This attribute group is only present for states that can be
used in suspend-to-idle with suspended timekeeping.
What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/time
Date: March 2018
KernelVersion: v4.17
Contact: Linux power management list <linux-pm@vger.kernel.org>
Description:
Total time spent by the CPU in suspend-to-idle (with scheduler
tick suspended) after requesting this state.
What: /sys/devices/system/cpu/cpuX/cpuidle/stateN/s2idle/usage
Date: March 2018
KernelVersion: v4.17
Contact: Linux power management list <linux-pm@vger.kernel.org>
Description:
Total number of times this state has been requested by the CPU
while entering suspend-to-idle.
What: /sys/devices/system/cpu/cpu#/cpufreq/*
Date: pre-git history
Contact: linux-pm@vger.kernel.org
Description: Discover and change clock speed of CPUs
Clock scaling allows you to change the clock speed of the
CPUs on the fly. This is a nice method to save battery
power, because the lower the clock speed, the less power
the CPU consumes.
There are many knobs to tweak in this directory.
See files in Documentation/cpu-freq/ for more information.
What: /sys/devices/system/cpu/cpu#/cpufreq/freqdomain_cpus
Date: June 2013
Contact: linux-pm@vger.kernel.org
Description: Discover CPUs in the same CPU frequency coordination domain
freqdomain_cpus is the list of CPUs (online+offline) that share
the same clock/freq domain (possibly at the hardware level).
That information may be hidden from the cpufreq core and the
value of related_cpus may be different from freqdomain_cpus. This
attribute is useful for user space DVFS controllers to get better
power/performance results for platforms using acpi-cpufreq.
This file is only present if the acpi-cpufreq driver is in use.
What: /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
Date: August 2008
KernelVersion: 2.6.27
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Disable L3 cache indices
These files exist in every CPU's cache/index3 directory. Each
cache_disable_{0,1} file corresponds to one disable slot which
can be used to disable a cache index. Reading from these files
on a processor with this functionality will return the currently
disabled index for that node. There is one L3 structure per
node, or per internal node on MCM machines. Writing a valid
index to one of these files will cause the specificed cache
index to be disabled.
All AMD processors with L3 caches provide this functionality.
For details, see BKDGs at
http://developer.amd.com/documentation/guides/Pages/default.aspx
What: /sys/devices/system/cpu/cpufreq/boost
Date: August 2012
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Processor frequency boosting control
This switch controls the boost setting for the whole system.
Boosting allows the CPU and the firmware to run at a frequency
beyound it's nominal limit.
More details can be found in
Documentation/admin-guide/pm/cpufreq.rst
What: /sys/devices/system/cpu/cpu#/crash_notes
/sys/devices/system/cpu/cpu#/crash_notes_size
Date: April 2013
Contact: kexec@lists.infradead.org
Description: address and size of the percpu note.
crash_notes: the physical address of the memory that holds the
note of cpu#.
crash_notes_size: size of the note of cpu#.
What: /sys/devices/system/cpu/intel_pstate/max_perf_pct
/sys/devices/system/cpu/intel_pstate/min_perf_pct
/sys/devices/system/cpu/intel_pstate/no_turbo
Date: February 2013
Contact: linux-pm@vger.kernel.org
Description: Parameters for the Intel P-state driver
Logic for selecting the current P-state in Intel
Sandybridge+ processors. The three knobs control
limits for the P-state that will be requested by the
driver.
max_perf_pct: limits the maximum P state that will be requested by
the driver stated as a percentage of the available performance.
min_perf_pct: limits the minimum P state that will be requested by
the driver stated as a percentage of the available performance.
no_turbo: limits the driver to selecting P states below the turbo
frequency range.
More details can be found in
Documentation/admin-guide/pm/intel_pstate.rst
What: /sys/devices/system/cpu/cpu*/cache/index*/<set_of_attributes_mentioned_below>
Date: July 2014(documented, existed before August 2008)
Contact: Sudeep Holla <sudeep.holla@arm.com>
Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Parameters for the CPU cache attributes
allocation_policy:
- WriteAllocate: allocate a memory location to a cache line
on a cache miss because of a write
- ReadAllocate: allocate a memory location to a cache line
on a cache miss because of a read
- ReadWriteAllocate: both writeallocate and readallocate
attributes: LEGACY used only on IA64 and is same as write_policy
coherency_line_size: the minimum amount of data in bytes that gets
transferred from memory to cache
level: the cache hierarchy in the multi-level cache configuration
number_of_sets: total number of sets in the cache, a set is a
collection of cache lines with the same cache index
physical_line_partition: number of physical cache line per cache tag
shared_cpu_list: the list of logical cpus sharing the cache
shared_cpu_map: logical cpu mask containing the list of cpus sharing
the cache
size: the total cache size in kB
type:
- Instruction: cache that only holds instructions
- Data: cache that only caches data
- Unified: cache that holds both data and instructions
ways_of_associativity: degree of freedom in placing a particular block
of memory in the cache
write_policy:
- WriteThrough: data is written to both the cache line
and to the block in the lower-level memory
- WriteBack: data is written only to the cache line and
the modified cache line is written to main
memory only when it is replaced
What: /sys/devices/system/cpu/cpu*/cache/index*/id
Date: September 2016
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Cache id
The id provides a unique number for a specific instance of
a cache of a particular type. E.g. there may be a level
3 unified cache on each socket in a server and we may
assign them ids 0, 1, 2, ...
Note that id value can be non-contiguous. E.g. level 1
caches typically exist per core, but there may not be a
power of two cores on a socket, so these caches may be
numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ...
What: /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/turbo_stat
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/sub_turbo_stat
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/unthrottle
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/powercap
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overtemp
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/supply_fault
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/overcurrent
/sys/devices/system/cpu/cpuX/cpufreq/throttle_stats/occ_reset
Date: March 2016
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
Description: POWERNV CPUFreq driver's frequency throttle stats directory and
attributes
'cpuX/cpufreq/throttle_stats' directory contains the CPU frequency
throttle stat attributes for the chip. The throttle stats of a cpu
is common across all the cpus belonging to a chip. Below are the
throttle attributes exported in the 'throttle_stats' directory:
- turbo_stat : This file gives the total number of times the max
frequency is throttled to lower frequency in turbo (at and above
nominal frequency) range of frequencies.
- sub_turbo_stat : This file gives the total number of times the
max frequency is throttled to lower frequency in sub-turbo(below
nominal frequency) range of frequencies.
- unthrottle : This file gives the total number of times the max
frequency is unthrottled after being throttled.
- powercap : This file gives the total number of times the max
frequency is throttled due to 'Power Capping'.
- overtemp : This file gives the total number of times the max
frequency is throttled due to 'CPU Over Temperature'.
- supply_fault : This file gives the total number of times the
max frequency is throttled due to 'Power Supply Failure'.
- overcurrent : This file gives the total number of times the
max frequency is throttled due to 'Overcurrent'.
- occ_reset : This file gives the total number of times the max
frequency is throttled due to 'OCC Reset'.
The sysfs attributes representing different throttle reasons like
powercap, overtemp, supply_fault, overcurrent and occ_reset map to
the reasons provided by OCC firmware for throttling the frequency.
What: /sys/devices/system/cpu/cpufreq/policyX/throttle_stats
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/turbo_stat
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/sub_turbo_stat
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/unthrottle
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/powercap
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overtemp
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/supply_fault
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/overcurrent
/sys/devices/system/cpu/cpufreq/policyX/throttle_stats/occ_reset
Date: March 2016
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
Description: POWERNV CPUFreq driver's frequency throttle stats directory and
attributes
'policyX/throttle_stats' directory and all the attributes are same as
the /sys/devices/system/cpu/cpuX/cpufreq/throttle_stats directory and
attributes which give the frequency throttle information of the chip.
What: /sys/devices/system/cpu/cpuX/regs/
/sys/devices/system/cpu/cpuX/regs/identification/
/sys/devices/system/cpu/cpuX/regs/identification/midr_el1
/sys/devices/system/cpu/cpuX/regs/identification/revidr_el1
Date: June 2016
Contact: Linux ARM Kernel Mailing list <linux-arm-kernel@lists.infradead.org>
Description: AArch64 CPU registers
'identification' directory exposes the CPU ID registers for
identifying model and revision of the CPU.
What: /sys/devices/system/cpu/cpu#/cpu_capacity
Date: December 2016
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: information about CPUs heterogeneity.
cpu_capacity: capacity of cpu#.
What: /sys/devices/system/cpu/vulnerabilities
/sys/devices/system/cpu/vulnerabilities/meltdown
/sys/devices/system/cpu/vulnerabilities/spectre_v1
/sys/devices/system/cpu/vulnerabilities/spectre_v2
/sys/devices/system/cpu/vulnerabilities/spec_store_bypass
/sys/devices/system/cpu/vulnerabilities/l1tf
/sys/devices/system/cpu/vulnerabilities/mds
Date: January 2018
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Information about CPU vulnerabilities
The files are named after the code names of CPU
vulnerabilities. The output of those files reflects the
state of the CPUs in the system. Possible output values:
"Not affected" CPU is not affected by the vulnerability
"Vulnerable" CPU is affected and no mitigation in effect
"Mitigation: $M" CPU is affected and mitigation $M is in effect
See also: Documentation/admin-guide/hw-vuln/index.rst
What: /sys/devices/system/cpu/smt
/sys/devices/system/cpu/smt/active
/sys/devices/system/cpu/smt/control
Date: June 2018
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Control Symetric Multi Threading (SMT)
active: Tells whether SMT is active (enabled and siblings online)
control: Read/write interface to control SMT. Possible
values:
"on" SMT is enabled
"off" SMT is disabled
"forceoff" SMT is force disabled. Cannot be changed.
"notsupported" SMT is not supported by the CPU
"notimplemented" SMT runtime toggling is not
implemented for the architecture
If control status is "forceoff" or "notsupported" writes
are rejected.
What: /sys/devices/system/cpu/cpu#/power/energy_perf_bias
Date: March 2019
Contact: linux-pm@vger.kernel.org
Description: Intel Energy and Performance Bias Hint (EPB)
EPB for the given CPU in a sliding scale 0 - 15, where a value
of 0 corresponds to a hint preference for highest performance
and a value of 15 corresponds to the maximum energy savings.
In order to change the EPB value for the CPU, write either
a number in the 0 - 15 sliding scale above, or one of the
strings: "performance", "balance-performance", "normal",
"balance-power", "power" (that represent values reflected by
their meaning), to this attribute.
This attribute is present for all online CPUs supporting the
Intel EPB feature.
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