[tip: perf/urgent] perf/x86/uncore: Correct the number of CHAs on EMR

[tip-bot2 for Kan Liang]

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     6f7f984fa85b305799076a1bcec941b9377587de
Gitweb:        https://git.kernel.org/tip/6f7f984fa85b305799076a1bcec941b9377587de
Author:        Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
AuthorDate:    Tue, 05 Sep 2023 06:42:48 -07:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 05 Sep 2023 21:50:21 +02:00

perf/x86/uncore: Correct the number of CHAs on EMR

Starting from SPR, the basic uncore PMON information is retrieved from
the discovery table (resides in an MMIO space populated by BIOS). It is
called the discovery method. The existing value of the type->num_boxes
is from the discovery table.

On some SPR variants, there is a firmware bug that makes the value from the
discovery table incorrect. We use the value from the
SPR_MSR_UNC_CBO_CONFIG MSR to replace the one from the discovery table:

   38776cc45eb7 ("perf/x86/uncore: Correct the number of CHAs on SPR")

Unfortunately, the SPR_MSR_UNC_CBO_CONFIG isn't available for the EMR
XCC (Always returns 0), but the above firmware bug doesn't impact the
EMR XCC.

Don't let the value from the MSR replace the existing value from the
discovery table.

Fixes: 38776cc45eb7 ("perf/x86/uncore: Correct the number of CHAs on SPR")
Reported-by: Stephane Eranian <eranian@xxxxxxxxxx>
Reported-by: Yunying Sun <yunying.sun@xxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Tested-by: Yunying Sun <yunying.sun@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230905134248.496114-1-kan.liang@xxxxxxxxxxxxxxx
---
 arch/x86/events/intel/uncore_snbep.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c
index 4d34998..8250f0f 100644
--- a/arch/x86/events/intel/uncore_snbep.c
+++ b/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);
 }