Re: [PATCH 1/2] arm_mpam: Force __iomem casts

Hi Krzysztof, Ben,

On 27/02/2026 14:51, Krzysztof Kozlowski wrote:

On 27/02/2026 15:06, Ben Horgan wrote:

quoted

On 2/16/26 11:02, Krzysztof Kozlowski wrote:

quoted

Code allocates standard kernel memory to pass to the MPAM, which expects
__iomem.  The code is safe, because __iomem accessors should work fine
on kernel mapped memory, however leads to sparse warnings:

  test_mpam_devices.c:327:42: warning: incorrect type in initializer (different address spaces)
  test_mpam_devices.c:327:42:    expected char [noderef] __iomem *buf
  test_mpam_devices.c:327:42:    got void *
  test_mpam_devices.c:342:24: warning: cast removes address space '__iomem' of expression

Cast the pointer to memory via __force to silence them.

quoted

quoted

diff --git a/drivers/resctrl/test_mpam_devices.c b/drivers/resctrl/test_mpam_devices.c
index 3e8d564a0c64..2de41b47c138 100644
--- a/drivers/resctrl/test_mpam_devices.c
+++ b/drivers/resctrl/test_mpam_devices.c

@@ -324,7 +324,7 @@ static void test_mpam_enable_merge_features(struct kunit *test)
 
 static void test_mpam_reset_msc_bitmap(struct kunit *test)
 {
-	char __iomem *buf = kunit_kzalloc(test, SZ_16K, GFP_KERNEL);
+	char __iomem *buf = (__force char __iomem *)kunit_kzalloc(test, SZ_16K, GFP_KERNEL);
 	struct mpam_msc fake_msc = {};
 	u32 *test_result;
 

quoted

This change looks good to me.

[...]

quoted

Acked-by: Ben Horgan <ben.horgan@arm.com>

Thanks! I've picked this for a fixes branch. I'm not sure what Will or Catalin will think
this needs fixing during the release as the driver is behind CONFIG_EXPERT. I'll ask...


Thanks,

James