Host CPU temperature in KVM guest

Yun-Chih Chen

I am trying to use to lm_sensorsdetect host CPU temperature in a KVM guest.

In the host, after inserting the x86_pkg_temp_thermal kernel module, the sysfs interface /sys/class/thermal/thermal_zone*/tempwill display the required information.

Here is the output of the sensors-detectscript on the host lm-sensors:

$ sudo sensors-detect
# sensors-detect revision 6284 (2015-05-31 14:00:33 +0200)
# System: LENOVO 20C60065TW [ThinkPad Edge E540] (laptop)
# Kernel: 4.8.8-200.fc24.x86_64 x86_64
# Processor: Intel(R) Core(TM) i7-4702MQ CPU @ 2.20GHz (6/60/3)

This program will help you determine which kernel modules you need
to load to use lm_sensors most effectively. It is generally safe
and recommended to accept the default answers to all questions,
unless you know what you're doing.

Some south bridges, CPUs or memory controllers contain embedded sensors.
Do you want to scan for them? This is totally safe. (YES/no): YES
Silicon Integrated Systems SIS5595...                       No
VIA VT82C686 Integrated Sensors...                          No
VIA VT8231 Integrated Sensors...                            No
AMD K8 thermal sensors...                                   No
AMD Family 10h thermal sensors...                           No
AMD Family 11h thermal sensors...                           No
AMD Family 12h and 14h thermal sensors...                   No
AMD Family 15h thermal sensors...                           No
AMD Family 16h thermal sensors...                           No
AMD Family 15h power sensors...                             No
AMD Family 16h power sensors...                             No
Intel digital thermal sensor...                             Success!
    (driver `coretemp')
Intel AMB FB-DIMM thermal sensor...                         No
Intel 5500/5520/X58 thermal sensor...                       No
VIA C7 thermal sensor...                                    No
VIA Nano thermal sensor...                                  No

In a KVM guest running Fedora 24, kernel modules cannot be inserted:

[root@fedora ~]# modprobe -v x86_pkg_temp_thermal
insmod /lib/modules/4.8.8300.fc25.x86_64/kernel/drivers/thermal/x86_pkg_temp_thermal.ko.xz 
modprobe: ERROR: could not insert 'x86_pkg_temp_thermal': No such device
[root@fedora ~]# modprobe -v coretemp
insmod /lib/modules/4.8.8-300.fc25.x86_64/kernel/drivers/hwmon/coretemp.ko.xz 
modprobe: ERROR: could not insert 'coretemp': No such device

sensors-detectThe output of the script in the guest indicates that the host has not exposed this feature.

[root@fedora ~]# sensors-detect 
# sensors-detect revision 6284 (2015-05-31 14:00:33 +0200)
# System: QEMU Standard PC (i440FX + PIIX, 1996) [pc-i440fx-2.6]
# Kernel: 4.8.8-300.fc25.x86_64 x86_64
# Processor: Westmere E56xx/L56xx/X56xx (Nehalem-C) (6/44/1)

This program will help you determine which kernel modules you need
to load to use lm_sensors most effectively. It is generally safe
and recommended to accept the default answers to all questions,
unless you know what you're doing.

Some south bridges, CPUs or memory controllers contain embedded sensors.
Do you want to scan for them? This is totally safe. (YES/no): YES
Silicon Integrated Systems SIS5595...                       No
VIA VT82C686 Integrated Sensors...                          No
VIA VT8231 Integrated Sensors...                            No
AMD K8 thermal sensors...                                   No
AMD Family 10h thermal sensors...                           No
AMD Family 11h thermal sensors...                           No
AMD Family 12h and 14h thermal sensors...                   No
AMD Family 15h thermal sensors...                           No
AMD Family 16h thermal sensors...                           No
AMD Family 15h power sensors...                             No
AMD Family 16h power sensors...                             No
Intel digital thermal sensor...                             No
Intel AMB FB-DIMM thermal sensor...                         No
Intel 5500/5520/X58 thermal sensor...                       No
VIA C7 thermal sensor...                                    No
VIA Nano thermal sensor...                                  No

Is there any way to expose the "Intel Digital Thermal Sensor" to the KVM guest?

Rui F Ribeiro

There should be no temperature in the virtual CPU, this is expected behavior.

CPUs in a VM are virtual and they may not map exactly one-to-one to real CPUs.

In virtual environments/VMs there are also expected differences/trade-offs, where a full emulation of the host environment is not expected to be found, and usually isn't even desirable for performance reasons.

So, for example, in some virtualization platforms extra effort is put into paravirtualizing network interface cards and disk controllers rather than simulating full hardware - the difference in performance can often be orders of magnitude.

In order to capture hardware data (i.e. temperature) and other monitoring data of the host, I recommend monitoring the host directly, such as configuring SNMP services, in addition to monitoring the VM.

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