From f63aaa529cbc73146ff0d52235e5479042285cae Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Tue, 6 Oct 2026 06:04:56 -0700 Subject: [PATCH] hwmon: (coretemp) Return -ENODATA for invalid temperature readings 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 f1a18a105660 ("Thermal: CPU Package temperature thermal"). This driver checked the bit for both registers as well, until commit bf6ea084ebb5 ("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 Link: https://lore.kernel.org/all/46f9f319-de71-412f-a424-6cb801478456@roeck-us.net/ Signed-off-by: Ricardo Neri Link: https://patch.msgid.link/20261006-coretemp-enodata-v2-1-64e788acc7dc@linux.intel.com Signed-off-by: Guenter Roeck --- Documentation/hwmon/coretemp.rst | 3 +++ drivers/hwmon/coretemp.c | 21 +++++++++++++++------ 2 files changed, 18 insertions(+), 6 deletions(-) diff --git a/Documentation/hwmon/coretemp.rst b/Documentation/hwmon/coretemp.rst index 349301683381..09f885a847e3 100644 --- a/Documentation/hwmon/coretemp.rst +++ b/Documentation/hwmon/coretemp.rst @@ -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). diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c index ace51e08e72d..bee2c9896d4c 100644 --- a/drivers/hwmon/coretemp.c +++ b/drivers/hwmon/coretemp.c @@ -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)