Subject: [PATCH v7 04/15] arm64: mm: Preserve existing table mappings when mapping DRAM

From: Ard Biesheuvel <[email-masked]>
Date: Fri, 29 May 2026 17:01:55 +0200

From: Ard Biesheuvel <[email-masked]>

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 <[email-masked]>
Signed-off-by: Ard Biesheuvel <[email-masked]>
---
 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 b2ba5b35c35f..5c827fa3cd38 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -256,7 +256,8 @@ 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)) {
 			WARN_ON(!pmd_set_huge(pmdp, phys, prot));
 
 			/*
@@ -379,7 +380,8 @@ 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)) {
 			WARN_ON(!pud_set_huge(pudp, phys, prot));
 
 			/*
-- 
2.54.0.823.g6e5bcc1fc9-goog