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mm/huge_memory: check pmd_special() only after pmd_present()

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We should only check for pmd_special() after we made sure that we have a
present PMD.  For example, if we have a migration PMD, pmd_special() might
indicate that we have a special PMD although we really don't.

This fixes confusing migration entries as PFN mappings, and not doing what
we are supposed to do in the "is_swap_pmd()" case further down in the
function -- including messing up COW, page table handling and accounting.

Link: https://lkml.kernel.org/r/20240926154234.2247217-1-david@redhat.com
Fixes: bc02afbd4d ("mm/fork: accept huge pfnmap entries")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: syzbot+bf2c35fa302ebe3c7471@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/66f15c8d.050a0220.c23dd.000f.GAE@google.com/
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2024-09-26 17:42:34 +02:00 committed by Andrew Morton
parent 0665d7a39b
commit 47fa30118f
1 changed files with 1 additions and 1 deletions
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2
mm/huge_memory.c
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@ -1586,7 +1586,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
int ret = -ENOMEM;
pmd = pmdp_get_lockless(src_pmd);
if (unlikely(pmd_special(pmd))) {
if (unlikely(pmd_present(pmd) && pmd_special(pmd))) {
dst_ptl = pmd_lock(dst_mm, dst_pmd);
src_ptl = pmd_lockptr(src_mm, src_pmd);
spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);