The patch titled
Subject: mm/huge_memory: conditionally call maybe_mkwrite() and drop pte_wrprotect() in __split_huge_pmd_locked()
has been added to the -mm mm-unstable branch. Its filename is
mm-huge_memory-conditionally-call-maybe_mkwrite-and-drop-pte_wrprotect-in-__split_huge_pmd_locked.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-conditionally-call-maybe_mkwrite-and-drop-pte_wrprotect-in-__split_huge_pmd_locked.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/huge_memory: conditionally call maybe_mkwrite() and drop pte_wrprotect() in __split_huge_pmd_locked()
Date: Tue, 11 Apr 2023 16:25:12 +0200
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/20230411142512.438404-7-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
--- a/mm/huge_memory.c~mm-huge_memory-conditionally-call-maybe_mkwrite-and-drop-pte_wrprotect-in-__split_huge_pmd_locked
+++ a/mm/huge_memory.c
@@ -2233,11 +2233,10 @@ static void __split_huge_pmd_locked(stru
entry = pte_swp_mkuffd_wp(entry);
} else {
entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
- entry = maybe_mkwrite(entry, vma);
+ 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 */
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries.patch
m68k-mm-use-correct-bit-number-in-_page_swp_exclusive-comment.patch
mm-userfaultfd-dont-consider-uffd-wp-bit-of-writable-migration-entries.patch
selftests-mm-reuse-read_pmd_pagesize-in-cow-selftest.patch
selftests-mm-mkdirty-test-behavior-of-ptepmd_mkdirty-on-vmas-without-write-permissions.patch
sparc-mm-dont-unconditionally-set-hw-writable-bit-when-setting-pte-dirty-on-64bit.patch
mm-migrate-revert-mm-migrate-fix-wrongly-apply-write-bit-after-mkdirty-on-sparc64.patch
mm-huge_memory-revert-partly-revert-mm-thp-carry-over-dirty-bit-when-thp-splits-on-pmd.patch
mm-huge_memory-conditionally-call-maybe_mkwrite-and-drop-pte_wrprotect-in-__split_huge_pmd_locked.patch
