Accesses to MSC must be made from a cpu that is affine to that MSC and the
driver checks this in __mpam_write_reg() using smp_processor_id(). A fake
in-memory MSC is used for testing. When using that, it doesn't matter which
cpu we access it from but calling smp_processor_id() from a preemptible
context gives warnings when running with CONFIG_DEBUG_PREEMPT.

Add a test helper that wraps mpam_reset_msc_bitmap() with preemption
disabled to ensure all (fake) MSC accesses are made with preemption
disabled.

Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
 drivers/resctrl/test_mpam_devices.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/resctrl/test_mpam_devices.c b/drivers/resctrl/test_mpam_devices.c
index 3e8d564a0c64..75bd41bcc395 100644
--- a/drivers/resctrl/test_mpam_devices.c
+++ b/drivers/resctrl/test_mpam_devices.c
@@ -322,6 +322,14 @@ static void test_mpam_enable_merge_features(struct kunit *test)
 	mutex_unlock(&mpam_list_lock);
 }
 
+static void __test_mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
+{
+	/* Avoid warnings when running with CONFIG_DEBUG_PREEMPT */
+	guard(preempt)();
+
+	mpam_reset_msc_bitmap(msc, reg, wd);
+}
+
 static void test_mpam_reset_msc_bitmap(struct kunit *test)
 {
 	char __iomem *buf = kunit_kzalloc(test, SZ_16K, GFP_KERNEL);
@@ -341,31 +349,31 @@ static void test_mpam_reset_msc_bitmap(struct kunit *test)
 
 	test_result = (u32 *)(buf + MPAMCFG_CPBM);
 
-	mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 0);
+	__test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 0);
 	KUNIT_EXPECT_EQ(test, test_result[0], 0);
 	KUNIT_EXPECT_EQ(test, test_result[1], 0);
 	test_result[0] = 0;
 	test_result[1] = 0;
 
-	mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 1);
+	__test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 1);
 	KUNIT_EXPECT_EQ(test, test_result[0], 1);
 	KUNIT_EXPECT_EQ(test, test_result[1], 0);
 	test_result[0] = 0;
 	test_result[1] = 0;
 
-	mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 16);
+	__test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 16);
 	KUNIT_EXPECT_EQ(test, test_result[0], 0xffff);
 	KUNIT_EXPECT_EQ(test, test_result[1], 0);
 	test_result[0] = 0;
 	test_result[1] = 0;
 
-	mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 32);
+	__test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 32);
 	KUNIT_EXPECT_EQ(test, test_result[0], 0xffffffff);
 	KUNIT_EXPECT_EQ(test, test_result[1], 0);
 	test_result[0] = 0;
 	test_result[1] = 0;
 
-	mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 33);
+	__test_mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 33);
 	KUNIT_EXPECT_EQ(test, test_result[0], 0xffffffff);
 	KUNIT_EXPECT_EQ(test, test_result[1], 1);
 	test_result[0] = 0;
-- 
2.43.0

Hi Ben,

On 27/02/2026 11:03, Ben Horgan wrote:
> Accesses to MSC must be made from a cpu that is affine to that MSC and the
> driver checks this in __mpam_write_reg() using smp_processor_id(). A fake
> in-memory MSC is used for testing. When using that, it doesn't matter which
> cpu we access it from but calling smp_processor_id() from a preemptible
> context gives warnings when running with CONFIG_DEBUG_PREEMPT.

Bah!


> Add a test helper that wraps mpam_reset_msc_bitmap() with preemption
> disabled to ensure all (fake) MSC accesses are made with preemption
> disabled.

> diff --git a/drivers/resctrl/test_mpam_devices.c b/drivers/resctrl/test_mpam_devices.c
> index 3e8d564a0c64..75bd41bcc395 100644
> --- a/drivers/resctrl/test_mpam_devices.c
> +++ b/drivers/resctrl/test_mpam_devices.c
> @@ -322,6 +322,14 @@ static void test_mpam_enable_merge_features(struct kunit *test)
>  	mutex_unlock(&mpam_list_lock);
>  }
>  
> +static void __test_mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
> +{
> +	/* Avoid warnings when running with CONFIG_DEBUG_PREEMPT */
> +	guard(preempt)();
> +
> +	mpam_reset_msc_bitmap(msc, reg, wd);
> +}
Reviewed-by: James Morse <james.morse@arm.com>


Thanks,

James