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    Subject[PATCH] hwmon: coretemp: avoid RDMSR interruptions to isolated CPUs

    The coretemp driver uses rdmsr_on_cpu calls to read
    MSR_IA32_PACKAGE_THERM_STATUS/MSR_IA32_THERM_STATUS registers,
    which contain information about current core temperature.

    For certain low latency applications, the RDMSR interruption exceeds
    the applications requirements.

    So disable reading of crit_alarm and temp files via /sys, in case
    CPU isolation is enabled.

    Temperature information from the housekeeping cores should be
    sufficient to infer die temperature.

    Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

    diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
    index 9bee4d33fbdf..30a35f4130d5 100644
    --- a/drivers/hwmon/coretemp.c
    +++ b/drivers/hwmon/coretemp.c
    @@ -27,6 +27,7 @@
    #include <asm/msr.h>
    #include <asm/processor.h>
    #include <asm/cpu_device_id.h>
    +#include <linux/sched/isolation.h>

    #define DRVNAME "coretemp"

    @@ -121,6 +122,10 @@ static ssize_t show_crit_alarm(struct device *dev,
    struct platform_data *pdata = dev_get_drvdata(dev);
    struct temp_data *tdata = pdata->core_data[attr->index];

    +
    + if (!housekeeping_cpu(tdata->cpu, HK_TYPE_MISC))
    + return -EINVAL;
    +
    mutex_lock(&tdata->update_lock);
    rdmsr_on_cpu(tdata->cpu, tdata->status_reg, &eax, &edx);
    mutex_unlock(&tdata->update_lock);
    @@ -158,6 +163,8 @@ static ssize_t show_temp(struct device *dev,

    /* Check whether the time interval has elapsed */
    if (!tdata->valid || time_after(jiffies, tdata->last_updated + HZ)) {
    + if (!housekeeping_cpu(tdata->cpu, HK_TYPE_MISC))
    + return -EINVAL;
    rdmsr_on_cpu(tdata->cpu, tdata->status_reg, &eax, &edx);
    /*
    * Ignore the valid bit. In all observed cases the register



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