On Mon, 31 Jan 2022 07:17:57 +0000, Christophe Leroy wrote:

On book3s/32 MMU, PP bits don't offer kernel RO protection,
kernel pages are always RW.

However, on the 603 a page fault is always generated when the
C bit (change bit = dirty bit) is not set.

Enforce kernel RO protection by clearing C bit in TLB miss
handler when the page doesn't have _PAGE_RW flag.

[...]

Applied to powerpc/next.

[1/1] powerpc/603: Clear C bit when PTE is read only
      https://git.kernel.org/powerpc/c/4634bf4455fe26f07dabf97c3585c9ccb86353c4

cheers