mm/huge_memory: conditionally call maybe_mkwrite() and drop pte_wrprotect() in __split_huge_pmd_locked()

No need to call maybe_mkwrite() to then wrprotect if the source PMD was not
writable.

It's worth nothing that this now allows for PTEs to be writable even if
the source PMD was not writable: if vma->vm_page_prot includes write
permissions.

As documented in commit 931298e103c2 ("mm/userfaultfd: rely on
vma->vm_page_prot in uffd_wp_range()"), any mechanism that intends to
have pages wrprotected (COW, writenotify, mprotect, uffd-wp, softdirty,
...) has to properly adjust vma->vm_page_prot upfront, to not include
write permissions. If vma->vm_page_prot includes write permissions, the
PTE/PMD can be writable as default.

This now mimics the handling in mm/migrate.c:remove_migration_pte() and in
mm/huge_memory.c:remove_migration_pmd(), which has been in place for a
long time (except that 96a9c287e25d ("mm/migrate: fix wrongly apply write
bit after mkdirty on sparc64") temporarily changed it).

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Sam Ravnborg <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Yu Zhao <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions