Where arch_needs_pgtable_deposit() is true, every huge PMD needs a
deposited page table. ppc64 in hash mode keeps the hash slot array of
the huge page in it, so vmf_insert_pfn_pmd() deposits one for each
special PMD it maps.
copy_huge_pmd() copies a special PMD into the child without a table.
The child then dereferences a NULL table:
- on the first hash fault on the PMD, in __hash_page_thp();
- on the zap at munmap() or exit, in hash__pmdp_huge_get_and_clear().
Allocate a table before taking the page table locks and deposit it
with the copy, as insert_pmd() does.
Fixes: d1503aa9ab805 ("powerpc/64s: Add support for huge pfnmaps")
Reported-by: Sashiko <[email protected]>
Closes:
https://sashiko.dev/#/patchset/20261014-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v1-1-d225c60bc...@virtuozzo.com?part=1
Cc: [email protected]
Assisted-by: LLM
Signed-off-by: Konstantin Khorenko <[email protected]>
---
mm/huge_memory.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index bf788bb231691..2380e4e877f82 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1961,6 +1961,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct
mm_struct *src_mm,
pmd = pmdp_get_lockless(src_pmd);
if (unlikely(pmd_present(pmd) && pmd_special(pmd) &&
!is_huge_zero_pmd(pmd))) {
+ if (arch_needs_pgtable_deposit()) {
+ pgtable = pte_alloc_one(dst_mm);
+ if (unlikely(!pgtable))
+ goto out;
+ }
dst_ptl = pmd_lock(dst_mm, dst_pmd);
src_ptl = pmd_lockptr(src_mm, src_pmd);
spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
@@ -1974,6 +1979,8 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct
mm_struct *src_mm,
if (unlikely(pmd_none(pmd))) {
spin_unlock(src_ptl);
spin_unlock(dst_ptl);
+ if (pgtable)
+ pte_free(dst_mm, pgtable);
return -EAGAIN;
}
/*
@@ -1983,6 +1990,10 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct
mm_struct *src_mm,
* wrongly write to the backend MMIO.
*/
VM_WARN_ON_ONCE(vma_is_cow_mapping(src_vma) && pmd_write(pmd));
+ if (pgtable) {
+ mm_inc_nr_ptes(dst_mm);
+ pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
+ }
goto set_pmd;
}
--
2.43.0
