[RFC PATCH 0/3] make persistent huge zero folio read-only

[Xueyuan chen]

From: Xueyuan Chen <xueyuan.chen21@xxxxxxxxx>

Hi all,

This series makes the persistent huge zero folio read-only in the direct
map.

The motivation comes from Jann Horn's read-only zero page work[1] and the
follow-up discussion[2] with Yang Shi. As Jann pointed out, the kernel has
had bugs, including security bugs, where pages taken with read-only
semantics were later written to. For the huge zero folio, making the direct
map read-only turns such writes into faults instead of silently corrupting
shared zero contents.

The permission change is best effort. If the architecture cannot safely
make the direct map read-only, the kernel keeps using the writable
persistent huge zero folio.

Patch 1 adds the generic support for making the persistent huge zero folio
read-only. Patches 2 and 3 add arm64 and x86 support.

[1] https://lore.kernel.org/linux-mm/20260508-ro-zeropage-v1-1-9808abc20b49@xxxxxxxxxx/
[2] https://lore.kernel.org/linux-mm/CAHbLzkrXXe7r3n3jXgDKtwZhRqj=jDx9E6dLOULohnhBguvi9A@xxxxxxxxxxxxxx/

Xueyuan Chen (3):
  mm: make persistent huge zero folio read-only
  arm64/mm: make huge zero folio read-only in linear map
  x86/mm: make huge zero folio read-only in direct map

 arch/arm64/Kconfig       |  1 +
 arch/arm64/mm/pageattr.c | 16 ++++++++++++++++
 arch/x86/Kconfig         |  1 +
 arch/x86/mm/init.c       | 11 +++++++++++
 include/linux/huge_mm.h  |  5 +++++
 mm/Kconfig               | 17 +++++++++++++++++
 mm/huge_memory.c         | 25 ++++++++++++++++++++++++-
 7 files changed, 75 insertions(+), 1 deletion(-)

-- 
2.47.3