[PATCH v3 02/47] arm_mpam: Use non-atomic bitops when modifying feature bitmap

Ben Horgan
2026-01-12T17:00:01Z

In the test__props_mismatch() kunit test we rely on the struct mpam_props
being packed to ensure memcmp doesn't consider packing. Making it packed
reduces the alignment of the features bitmap and so breaks a requirement
for the use of atomics. As we don't rely on the set/clear of these bits
being atomic, just make them non-atomic.

Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since v2:
Add comment (Jonathan)
---
drivers/resctrl/mpam_internal.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 17cdc3080d58..e8971842b124 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -200,8 +200,12 @@ struct mpam_props {
} PACKED_FOR_KUNIT;

#define mpam_has_feature(_feat, x) test_bit(_feat, (x)->features)
-#define mpam_set_feature(_feat, x) set_bit(_feat, (x)->features)
-#define mpam_clear_feature(_feat, x) clear_bit(_feat, (x)->features)
+/*
+ * The non-atomic get/set operations are used because if struct mpam_props is
+ * packed, the alignment requirements for atomics aren't met.
+ */
+#define mpam_set_feature(_feat, x) __set_bit(_feat, (x)->features)
+#define mpam_clear_feature(_feat, x) __clear_bit(_feat, (x)->features)

/* The values for MSMON_CFG_MBWU_FLT.RWBW */
enum mon_filter_options {
--
2.43.0