coretemp: Only log critical temperature events

According to the Intel manual
https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-3b-part-2-manual.pdf
the Thermal Status (0) and Thermal Status Log (1) bits report only a
high temperature on the CPU, not a critical temperature as suggested in
the coretemp driver. Check the Critical Temperature Log (5) instead.
The critical temperature waives guarantees of correct function,
therefore the CPU could have for example written some wrong values into
memory at that point and the OS should be stopped ASAP as the state is
no longer reliable.

Reviewed by: imp (confirmed descriptions of bits, linux ignores these bits)
Pull Request: #562

sys/dev/coretemp/coretemp.c

@@ -53,6 +53,8 @@ __FBSDID("$FreeBSD$");
 
 #define	TZ_ZEROC			2731
 
+#define	THERM_CRITICAL_STATUS_LOG       0x20
+#define	THERM_CRITICAL_STATUS           0x10
 #define	THERM_STATUS_LOG		0x02
 #define	THERM_STATUS			0x01
 #define	THERM_STATUS_TEMP_SHIFT		16
@@ -393,7 +395,7 @@ coretemp_get_val_sysctl(SYSCTL_HANDLER_ARGS)
 		 * If we reach a critical level, allow devctl(4)
 		 * to catch this and shutdown the system.
 		 */
-		if (msr & THERM_STATUS) {
+		if (msr & THERM_CRITICAL_STATUS) {
 			tmp = (msr >> THERM_STATUS_TEMP_SHIFT) &
 			    THERM_STATUS_TEMP_MASK;
 			tmp = (sc->sc_tjmax - tmp) * 10 + TZ_ZEROC;