# \[PATCH v2 46/69\] mm/sparse-vmemmap: Map shared vmemmap tail pages read-only

- From: Muchun Song \<hidden\>
- Date: 2026-05-13 13:11:46 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2026/05/9003641
- Thread: https://ratatoskr.run/linux-mm/2026/05/9003574/t.md

```text
Shared vmemmap tail pages are now installed through
vmemmap_pte_populate().

Map those shared 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>
---
 mm/sparse-vmemmap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 182d0c7dd1e7..9811c92ad258 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -158,7 +158,8 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, in
 		if (slab_is_available())
 			get_page(page);
 
-		entry = pfn_pte(page_to_pfn(page), PAGE_KERNEL);
+		/* Map shared tail page read-only to catch illegal writes. */
+		entry = pfn_pte(page_to_pfn(page), PAGE_KERNEL_RO);
 	} else {
 		void *vaddr = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
 
-- 
2.54.0


```