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

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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 931298e103 ("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 96a9c287e2 ("mm/migrate: fix wrongly apply write
bit after mkdirty on sparc64") temporarily changed it).

Link: https://lkml.kernel.org/r/20230411142512.438404-7-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2023-04-11 16:25:12 +02:00 committed by Andrew Morton
parent 5436d65569
commit 1462c52e9f
1 changed files with 2 additions and 3 deletions
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3
mm/huge_memory.c
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@ -2233,11 +2233,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
entry = pte_swp_mkuffd_wp(entry);
} else {
entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
if (write)
entry = maybe_mkwrite(entry, vma);
if (anon_exclusive)
SetPageAnonExclusive(page + i);
if (!write)
entry = pte_wrprotect(entry);
if (!young)
entry = pte_mkold(entry);
/* NOTE: this may set soft-dirty too on some archs */