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hwmon: (coretemp) Return -ENODATA for invalid temperature readings

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IA32_THERM_STATUS and IA32_PACKAGE_THERM_STATUS have a valid bit, bit 31.
The Intel SDM documents it only for the former, but the package register
implements it too: x86_pkg_temp_thermal has required it since commit
f1a18a1056 ("Thermal: CPU Package temperature thermal").

This driver checked the bit for both registers as well, until
commit bf6ea084eb ("hwmon: (coretemp) Do not return -EAGAIN for low
temperatures") made it ignore the bit because some CPUs clear it while
the temperature is too low to be measured. Since then, temp%d_input
reports such a reading as a real temperature. Userspace cannot tell it
apart from a genuinely low one.

Fail the read with -ENODATA while the CPU reports the reading as invalid.
On a CPU that clears the bit, reading temp%d_input now fails where it
used to return a low value. sensors(1) shows N/A in its place.

Cc: stable@vger.kernel.org
Suggested-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/all/46f9f319-de71-412f-a424-6cb801478456@roeck-us.net/
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Link: https://patch.msgid.link/20261006-coretemp-enodata-v2-1-64e788acc7dc@linux.intel.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Ricardo Neri 2026-10-06 06:04:56 -07:00 committed by Guenter Roeck
parent ce3ff350c4
commit f63aaa529c
2 changed files with 18 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
Documentation/hwmon/coretemp.rst
View File

@ -50,6 +50,9 @@ All sysfs entries are named with their core_id (represented here by 'X').
================= ========================================================
tempX_input Core temperature (in millidegrees Celsius).
Reading fails with -ENODATA while the CPU reports the
temperature as invalid. Some CPUs do this when the
temperature is too low to be measured.
tempX_max Maximum recommended operating temperature (Tcontrol).
All cooling devices should be turned on.
tempX_crit Maximum junction temperature (in millidegrees Celsius).

21
drivers/hwmon/coretemp.c
View File

@ -60,6 +60,8 @@ enum coretemp_attr_index {
/*
* Per-Core Temperature Data
* @temp_valid: Whether the CPU reported @temp as valid. @temp is not
* reported when this is false.
* @tjmax: The static tjmax value when tjmax cannot be retrieved from
* IA32_TEMPERATURE_TARGET MSR.
* @last_updated: The time when the current temperature value was updated
@ -72,6 +74,7 @@ enum coretemp_attr_index {
*/
struct temp_data {
int temp;
bool temp_valid;
int tjmax;
unsigned long last_updated;
unsigned int cpu;
@ -398,7 +401,8 @@ static ssize_t show_temp(struct device *dev,
{
struct msr val;
struct temp_data *tdata = container_of(devattr, struct temp_data, sd_attrs[ATTR_TEMP]);
int tjmax;
int tjmax, temp;
bool valid;
mutex_lock(&tdata->update_lock);
@ -407,17 +411,22 @@ static ssize_t show_temp(struct device *dev,
if (time_after(jiffies, tdata->last_updated + HZ)) {
rdmsrq_on_cpu(tdata->cpu, tdata->status_reg, &val.q);
/*
* Ignore the valid bit. In all observed cases the register
* value is either low or zero if the valid bit is 0.
* Return it instead of reporting an error which doesn't
* really help at all.
* Bit 31 indicates whether the reading is valid. Some CPUs
* clear it while the temperature is too low to be measured.
* Such a reading is not a temperature. Do not report it.
*/
tdata->temp_valid = (val.l >> 31) & 1;
tdata->temp = tjmax - ((val.l >> 16) & 0xff) * 1000;
tdata->last_updated = jiffies;
}
valid = tdata->temp_valid;
temp = tdata->temp;
mutex_unlock(&tdata->update_lock);
return sprintf(buf, "%d\n", tdata->temp);
if (!valid)
return -ENODATA;
return sprintf(buf, "%d\n", temp);
}
static int create_core_attrs(struct temp_data *tdata, struct device *dev)