Merge tag 'perf-urgent-2023-09-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 perf event fix from Ingo Molnar:
 "Work around a firmware bug in the uncore PMU driver, affecting certain
  Intel systems"

* tag 'perf-urgent-2023-09-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/x86/uncore: Correct the number of CHAs on EMR

Author: torvalds

arch/x86/events/intel/uncore_snbep.c

@@ -6474,8 +6474,18 @@ void spr_uncore_cpu_init(void)
 
 	type = uncore_find_type_by_id(uncore_msr_uncores, UNCORE_SPR_CHA);
 	if (type) {
+		/*
+		 * The value from the discovery table (stored in the type->num_boxes
+		 * of UNCORE_SPR_CHA) is incorrect on some SPR variants because of a
+		 * firmware bug. Using the value from SPR_MSR_UNC_CBO_CONFIG to replace it.
+		 */
 		rdmsrl(SPR_MSR_UNC_CBO_CONFIG, num_cbo);
-		type->num_boxes = num_cbo;
+		/*
+		 * The MSR doesn't work on the EMR XCC, but the firmware bug doesn't impact
+		 * the EMR XCC. Don't let the value from the MSR replace the existing value.
+		 */
+		if (num_cbo)
+			type->num_boxes = num_cbo;
 	}
 	spr_uncore_iio_free_running.num_boxes = uncore_type_max_boxes(uncore_msr_uncores, UNCORE_SPR_IIO);
 }