# \[PATCH v2 47/69\] powerpc/mm: Map shared vmemmap tail pages read-only

- From: Muchun Song \<hidden\>
- Date: 2026-05-13 13:20:58 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2026/05/9003709
- Thread: https://ratatoskr.run/linux-mm/2026/05/9003574/t.md

```text
Shared vmemmap tail pages can also be installed through the powerpc
radix vmemmap populate path.

Map reused tail pages with PAGE_KERNEL_RO so writes to shared tail
vmemmap entries fault immediately instead of silently corrupting shared
metadata.

Signed-off-by: Muchun Song <redacted>
---
 arch/powerpc/mm/book3s64/radix_pgtable.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
index 18b24bb891b7..4c3d027c823c 100644
--- a/arch/powerpc/mm/book3s64/radix_pgtable.c
+++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -1053,7 +1053,8 @@ static pte_t * __meminit radix__vmemmap_pte_populate(pmd_t *pmdp, unsigned long
 		}
 
 		VM_BUG_ON(!PAGE_ALIGNED(addr));
-		entry = pfn_pte(__pa(p) >> PAGE_SHIFT, PAGE_KERNEL);
+		entry = pfn_pte(__pa(p) >> PAGE_SHIFT,
+				reuse ? PAGE_KERNEL_RO : PAGE_KERNEL);
 		set_pte_at(&init_mm, addr, pte, entry);
 		asm volatile("ptesync": : :"memory");
 	}
-- 
2.54.0


```