Current implementation of UFFDIO_MOVE fails to move zeropages and returns
EBUSY when it encounters one. We can handle them by mapping a zeropage
at the destination and clearing the mapping at the source. This is done
both for ordinary and for huge zeropages.
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
Applies cleanly over mm-unstable branch.
mm/huge_memory.c | 105 +++++++++++++++++++++++++++--------------------
mm/userfaultfd.c | 42 +++++++++++++++----
2 files changed, 96 insertions(+), 51 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f40feb31b507..5dcc02c25e97 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2190,13 +2190,18 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm
}
src_page = pmd_page(src_pmdval);
- if (unlikely(!PageAnonExclusive(src_page))) {
- spin_unlock(src_ptl);
- return -EBUSY;
- }
- src_folio = page_folio(src_page);
- folio_get(src_folio);
+ if (!is_huge_zero_pmd(src_pmdval)) {
+ if (unlikely(!PageAnonExclusive(src_page))) {
+ spin_unlock(src_ptl);
+ return -EBUSY;
+ }
+
+ src_folio = page_folio(src_page);
+ folio_get(src_folio);
+ } else
+ src_folio = NULL;
+
spin_unlock(src_ptl);
flush_cache_range(src_vma, src_addr, src_addr + HPAGE_PMD_SIZE);
@@ -2204,19 +2209,22 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm
src_addr + HPAGE_PMD_SIZE);
mmu_notifier_invalidate_range_start(&range);
- folio_lock(src_folio);
+ if (src_folio) {
+ folio_lock(src_folio);
- /*
- * split_huge_page walks the anon_vma chain without the page
- * lock. Serialize against it with the anon_vma lock, the page
- * lock is not enough.
- */
- src_anon_vma = folio_get_anon_vma(src_folio);
- if (!src_anon_vma) {
- err = -EAGAIN;
- goto unlock_folio;
- }
- anon_vma_lock_write(src_anon_vma);
+ /*
+ * split_huge_page walks the anon_vma chain without the page
+ * lock. Serialize against it with the anon_vma lock, the page
+ * lock is not enough.
+ */
+ src_anon_vma = folio_get_anon_vma(src_folio);
+ if (!src_anon_vma) {
+ err = -EAGAIN;
+ goto unlock_folio;
+ }
+ anon_vma_lock_write(src_anon_vma);
+ } else
+ src_anon_vma = NULL;
dst_ptl = pmd_lockptr(mm, dst_pmd);
double_pt_lock(src_ptl, dst_ptl);
@@ -2225,45 +2233,54 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm
err = -EAGAIN;
goto unlock_ptls;
}
- if (folio_maybe_dma_pinned(src_folio) ||
- !PageAnonExclusive(&src_folio->page)) {
- err = -EBUSY;
- goto unlock_ptls;
- }
+ if (src_folio) {
+ if (folio_maybe_dma_pinned(src_folio) ||
+ !PageAnonExclusive(&src_folio->page)) {
+ err = -EBUSY;
+ goto unlock_ptls;
+ }
- if (WARN_ON_ONCE(!folio_test_head(src_folio)) ||
- WARN_ON_ONCE(!folio_test_anon(src_folio))) {
- err = -EBUSY;
- goto unlock_ptls;
- }
+ if (WARN_ON_ONCE(!folio_test_head(src_folio)) ||
+ WARN_ON_ONCE(!folio_test_anon(src_folio))) {
+ err = -EBUSY;
+ goto unlock_ptls;
+ }
- folio_move_anon_rmap(src_folio, dst_vma);
- WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
+ folio_move_anon_rmap(src_folio, dst_vma);
+ WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
- src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd);
- /* Folio got pinned from under us. Put it back and fail the move. */
- if (folio_maybe_dma_pinned(src_folio)) {
- set_pmd_at(mm, src_addr, src_pmd, src_pmdval);
- err = -EBUSY;
- goto unlock_ptls;
- }
+ src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd);
+ /* Folio got pinned from under us. Put it back and fail the move. */
+ if (folio_maybe_dma_pinned(src_folio)) {
+ set_pmd_at(mm, src_addr, src_pmd, src_pmdval);
+ err = -EBUSY;
+ goto unlock_ptls;
+ }
- _dst_pmd = mk_huge_pmd(&src_folio->page, dst_vma->vm_page_prot);
- /* Follow mremap() behavior and treat the entry dirty after the move */
- _dst_pmd = pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma);
+ _dst_pmd = mk_huge_pmd(&src_folio->page, dst_vma->vm_page_prot);
+ /* Follow mremap() behavior and treat the entry dirty after the move */
+ _dst_pmd = pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma);
+ } else {
+ src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd);
+ _dst_pmd = mk_huge_pmd(src_page, dst_vma->vm_page_prot);
+ }
set_pmd_at(mm, dst_addr, dst_pmd, _dst_pmd);
src_pgtable = pgtable_trans_huge_withdraw(mm, src_pmd);
pgtable_trans_huge_deposit(mm, dst_pmd, src_pgtable);
unlock_ptls:
double_pt_unlock(src_ptl, dst_ptl);
- anon_vma_unlock_write(src_anon_vma);
- put_anon_vma(src_anon_vma);
+ if (src_anon_vma) {
+ anon_vma_unlock_write(src_anon_vma);
+ put_anon_vma(src_anon_vma);
+ }
unlock_folio:
/* unblock rmap walks */
- folio_unlock(src_folio);
+ if (src_folio)
+ folio_unlock(src_folio);
mmu_notifier_invalidate_range_end(&range);
- folio_put(src_folio);
+ if (src_folio)
+ folio_put(src_folio);
return err;
}
#endif /* CONFIG_USERFAULTFD */
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 3548b3e31a97..5fbf4da15c5c 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -959,6 +959,31 @@ static int move_swap_pte(struct mm_struct *mm,
return 0;
}
+static int move_zeropage_pte(struct mm_struct *mm,
+ struct vm_area_struct *dst_vma,
+ struct vm_area_struct *src_vma,
+ unsigned long dst_addr, unsigned long src_addr,
+ pte_t *dst_pte, pte_t *src_pte,
+ pte_t orig_dst_pte, pte_t orig_src_pte,
+ spinlock_t *dst_ptl, spinlock_t *src_ptl)
+{
+ pte_t zero_pte;
+
+ double_pt_lock(dst_ptl, src_ptl);
+ if (!pte_same(ptep_get(src_pte), orig_src_pte) ||
+ !pte_same(ptep_get(dst_pte), orig_dst_pte))
+ return -EAGAIN;
+
+ zero_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
+ dst_vma->vm_page_prot));
+ ptep_clear_flush(src_vma, src_addr, src_pte);
+ set_pte_at(mm, dst_addr, dst_pte, zero_pte);
+ double_pt_unlock(dst_ptl, src_ptl);
+
+ return 0;
+}
+
+
/*
* The mmap_lock for reading is held by the caller. Just move the page
* from src_pmd to dst_pmd if possible, and return true if succeeded
@@ -1041,6 +1066,14 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
}
if (pte_present(orig_src_pte)) {
+ if (is_zero_pfn(pte_pfn(orig_src_pte))) {
+ err = move_zeropage_pte(mm, dst_vma, src_vma,
+ dst_addr, src_addr, dst_pte, src_pte,
+ orig_dst_pte, orig_src_pte,
+ dst_ptl, src_ptl);
+ goto out;
+ }
+
/*
* Pin and lock both source folio and anon_vma. Since we are in
* RCU read section, we can't block, so on contention have to
@@ -1404,19 +1437,14 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
err = -ENOENT;
break;
}
- /* Avoid moving zeropages for now */
- if (is_huge_zero_pmd(*src_pmd)) {
- spin_unlock(ptl);
- err = -EBUSY;
- break;
- }
/* Check if we can move the pmd without splitting it. */
if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
!pmd_none(dst_pmdval)) {
struct folio *folio = pfn_folio(pmd_pfn(*src_pmd));
- if (!folio || !PageAnonExclusive(&folio->page)) {
+ if (!folio || (!is_huge_zero_page(&folio->page) &&
+ !PageAnonExclusive(&folio->page))) {
spin_unlock(ptl);
err = -EBUSY;
break;
--
2.43.0.429.g432eaa2c6b-goog
