On Wed, Jan 31, 2024 at 1:27 AM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > The quilt patch titled > Subject: userfaultfd: handle zeropage moves by UFFDIO_MOVE > has been removed from the -mm tree. Its filename was > userfaultfd-handle-zeropage-moves-by-uffdio_move.patch > > This patch was dropped because an updated version will be merged Updated version v2 is posted at https://lore.kernel.org/all/20240131175618.2417291-1-surenb@xxxxxxxxxx/ > > ------------------------------------------------------ > From: Suren Baghdasaryan <surenb@xxxxxxxxxx> > Subject: userfaultfd: handle zeropage moves by UFFDIO_MOVE > Date: Wed, 24 Jan 2024 16:13:28 -0800 > > 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. > > Link: https://lkml.kernel.org/r/20240125001328.335127-1-surenb@xxxxxxxxxx > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> > Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> > Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> > Cc: Brian Geffon <bgeffon@xxxxxxxxxx> > Cc: Christian Brauner <brauner@xxxxxxxxxx> > Cc: David Hildenbrand <david@xxxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Jann Horn <jannh@xxxxxxxxxx> > Cc: Kalesh Singh <kaleshsingh@xxxxxxxxxx> > Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx> > Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> > Cc: Nicolas Geoffray <ngeoffray@xxxxxxxxxx> > Cc: Peter Xu <peterx@xxxxxxxxxx> > Cc: Ryan Roberts <ryan.roberts@xxxxxxx> > Cc: Shuah Khan <shuah@xxxxxxxxxx> > Cc: ZhangPeng <zhangpeng362@xxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > mm/huge_memory.c | 111 +++++++++++++++++++++++++-------------------- > mm/userfaultfd.c | 42 ++++++++++++++--- > 2 files changed, 99 insertions(+), 54 deletions(-) > > --- a/mm/huge_memory.c~userfaultfd-handle-zeropage-moves-by-uffdio_move > +++ a/mm/huge_memory.c > @@ -2200,13 +2200,18 @@ int move_pages_huge_pmd(struct mm_struct > } > > 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); > @@ -2214,19 +2219,22 @@ int move_pages_huge_pmd(struct mm_struct > 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); > @@ -2235,45 +2243,54 @@ int move_pages_huge_pmd(struct mm_struct > err = -EAGAIN; > goto unlock_ptls; > } > - 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; > - } > - > - 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; > + 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; > + } > + > + 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; > + } > + > + _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); > } > - > - _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); > 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 */ > --- a/mm/userfaultfd.c~userfaultfd-handle-zeropage-moves-by-uffdio_move > +++ a/mm/userfaultfd.c > @@ -959,6 +959,31 @@ static int move_swap_pte(struct mm_struc > 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 @@ retry: > } > > 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_ct > 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; > _ > > Patches currently in -mm which might be from surenb@xxxxxxxxxx are > > arch-arm-mm-fix-major-fault-accounting-when-retrying-under-per-vma-lock.patch >
