The patch titled
Subject: mm: khugepaged: collapse_pte_mapped_thp() use pte_offset_map_rw_nolock()
has been added to the -mm mm-unstable branch. Its filename is
mm-khugepaged-collapse_pte_mapped_thp-use-pte_offset_map_rw_nolock.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-collapse_pte_mapped_thp-use-pte_offset_map_rw_nolock.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: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Subject: mm: khugepaged: collapse_pte_mapped_thp() use pte_offset_map_rw_nolock()
Date: Thu, 26 Sep 2024 14:46:20 +0800
In collapse_pte_mapped_thp(), we may modify the pte and pmd entry after
acquiring the ptl, so convert it to using pte_offset_map_rw_nolock(). At
this time, the pte_same() check is not performed after the PTL held. So
we should get pgt_pmd and do pmd_same() check after the ptl held.
Link: https://lkml.kernel.org/r/055e42db68da00ac8ecab94bd2633c7cd965eb1c.1727332572.git.zhengqi.arch@xxxxxxxxxxxxx
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <muchun.song@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
--- a/mm/khugepaged.c~mm-khugepaged-collapse_pte_mapped_thp-use-pte_offset_map_rw_nolock
+++ a/mm/khugepaged.c
@@ -1608,7 +1608,7 @@ int collapse_pte_mapped_thp(struct mm_st
if (userfaultfd_armed(vma) && !(vma->vm_flags & VM_SHARED))
pml = pmd_lock(mm, pmd);
- start_pte = pte_offset_map_nolock(mm, pmd, haddr, &ptl);
+ start_pte = pte_offset_map_rw_nolock(mm, pmd, haddr, &pgt_pmd, &ptl);
if (!start_pte) /* mmap_lock + page lock should prevent this */
goto abort;
if (!pml)
@@ -1616,6 +1616,9 @@ int collapse_pte_mapped_thp(struct mm_st
else if (ptl != pml)
spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
+ if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd))))
+ goto abort;
+
/* step 2: clear page table and adjust rmap */
for (i = 0, addr = haddr, pte = start_pte;
i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
@@ -1648,7 +1651,6 @@ int collapse_pte_mapped_thp(struct mm_st
nr_ptes++;
}
- pte_unmap(start_pte);
if (!pml)
spin_unlock(ptl);
@@ -1661,14 +1663,19 @@ int collapse_pte_mapped_thp(struct mm_st
/* step 4: remove empty page table */
if (!pml) {
pml = pmd_lock(mm, pmd);
- if (ptl != pml)
+ if (ptl != pml) {
spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
+ if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd)))) {
+ flush_tlb_mm(mm);
+ goto unlock;
+ }
+ }
}
pgt_pmd = pmdp_collapse_flush(vma, haddr, pmd);
pmdp_get_lockless_sync();
+ pte_unmap_unlock(start_pte, ptl);
if (ptl != pml)
- spin_unlock(ptl);
- spin_unlock(pml);
+ spin_unlock(pml);
mmu_notifier_invalidate_range_end(&range);
@@ -1688,6 +1695,7 @@ abort:
folio_ref_sub(folio, nr_ptes);
add_mm_counter(mm, mm_counter_file(folio), -nr_ptes);
}
+unlock:
if (start_pte)
pte_unmap_unlock(start_pte, ptl);
if (pml && pml != ptl)
_
Patches currently in -mm which might be from zhengqi.arch@xxxxxxxxxxxxx are
mm-pgtable-introduce-pte_offset_map_rorw_nolock.patch
powerpc-assert_pte_locked-use-pte_offset_map_ro_nolock.patch
mm-filemap-filemap_fault_recheck_pte_none-use-pte_offset_map_ro_nolock.patch
mm-khugepaged-__collapse_huge_page_swapin-use-pte_offset_map_ro_nolock.patch
arm-adjust_pte-use-pte_offset_map_rw_nolock.patch
mm-handle_pte_fault-use-pte_offset_map_rw_nolock.patch
mm-khugepaged-collapse_pte_mapped_thp-use-pte_offset_map_rw_nolock.patch
mm-copy_pte_range-use-pte_offset_map_rw_nolock.patch
mm-mremap-move_ptes-use-pte_offset_map_rw_nolock.patch
mm-page_vma_mapped_walk-map_pte-use-pte_offset_map_rw_nolock.patch
mm-userfaultfd-move_pages_pte-use-pte_offset_map_rw_nolock.patch
mm-multi-gen-lru-walk_pte_range-use-pte_offset_map_rw_nolock.patch
mm-pgtable-remove-pte_offset_map_nolock.patch
