[PATCH v3 02/13] arm64: mm: Preserve existing table mappings when mapping DRAM

Ard Biesheuvel
2026-03-20T15:00:02Z

Instead of blindly overwriting an existing table entry when mapping DRAM
regions, take care not to replace a pre-existing table entry with a
block entry. This permits the logic of mapping the kernel's linear alias
to be simplified in a subsequent patch.

Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/mm/mmu.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 795743913ce5..9927b55022d8 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -262,7 +262,8 @@ static int init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,

/* try section mapping first */
if (((addr | next | phys) & ~PMD_MASK) == 0 &&
- (flags & NO_BLOCK_MAPPINGS) == 0) {
+ (flags & NO_BLOCK_MAPPINGS) == 0 &&
+ !pmd_table(old_pmd)) {
pmd_set_huge(pmdp, phys, prot);

/*
@@ -385,7 +386,8 @@ static int alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
*/
if (pud_sect_supported() &&
((addr | next | phys) & ~PUD_MASK) == 0 &&
- (flags & NO_BLOCK_MAPPINGS) == 0) {
+ (flags & NO_BLOCK_MAPPINGS) == 0 &&
+ !pud_table(old_pud)) {
pud_set_huge(pudp, phys, prot);

/*
--
2.53.0.959.g497ff81fa9-goog