Re: [PATCH 1/2] arm_mpam: Force __iomem casts
From: Ben Horgan <ben.horgan@arm.com>
Date: 2026-02-27 14:06:30
Also in:
lkml
Subsystem:
memory management - core, memory management - page allocator, the rest · Maintainers:
Andrew Morton, David Hildenbrand, Vlastimil Babka, Linus Torvalds
Hi Krzysztof, On 2/16/26 11:02, Krzysztof Kozlowski wrote:
quoted hunk ↗ jump to hunk
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. Signed-off-by: Krzysztof Kozlowski <redacted> --- drivers/resctrl/test_mpam_devices.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)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;@@ -339,7 +339,7 @@ static void test_mpam_reset_msc_bitmap(struct kunit *test) mutex_init(&fake_msc.part_sel_lock); mutex_lock(&fake_msc.part_sel_lock); - test_result = (u32 *)(buf + MPAMCFG_CPBM); + test_result = (__force u32 *)(buf + MPAMCFG_CPBM); mpam_reset_msc_bitmap(&fake_msc, MPAMCFG_CPBM, 0); KUNIT_EXPECT_EQ(test, test_result[0], 0);
This change looks good to me. As sparse is more broken I needed to use the patch from [1] to reproduce this. Copied here for convenience.
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 2b30a0529d48..90536b2bc42e 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h@@ -14,8 +14,8 @@ struct vm_area_struct; struct mempolicy; /* Helper macro to avoid gfp flags if they are the default one */ -#define __default_gfp(a,...) a -#define default_gfp(...) __default_gfp(__VA_ARGS__ __VA_OPT__(,)
GFP_KERNEL) +#define __default_gfp(a,b,...) b +#define default_gfp(...) __default_gfp(,##__VA_ARGS__,GFP_KERNEL) /* Convert GFP flags to their corresponding migrate type */ #define GFP_MOVABLE_MASK (__GFP_RECLAIMABLE|__GFP_MOVABLE) There is a kernel test robot report [2] and that asks for these tags: Reported-by: kernel test robot <redacted> Closes: https://lore.kernel.org/oe-kbuild-all/202512160133.eAzPdJv2-lkp@intel.com/ (local) Acked-by: Ben Horgan <ben.horgan@arm.com> [1] https://lore.kernel.org/all/CAHk-=wijD-giccF6sJ+BdJpGDX9kPEUT6kryaQG0GRyJ3QQwng@mail.gmail.com/ [2] https://lore.kernel.org/all/202512160133.eAzPdJv2-lkp@intel.com/ (local) Thanks, Ben