| Message ID | 20240125001328.335127-1-surenb@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] userfaultfd: handle zeropage moves by UFFDIO_MOVE | expand |
On Wed, Jan 24, 2024 at 4:13 PM Suren Baghdasaryan <surenb@google.com> wrote: > > 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. I made a stupid mistake when formatting this patch and it says [PATCH 1/2] but it should be the only patch in the set. So, please do not look for [2/2]. Sorry about the confusion. Thanks, Suren. > > Signed-off-by: Suren Baghdasaryan <surenb@google.com> > --- > 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 >
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;
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@google.com> --- Applies cleanly over mm-unstable branch. mm/huge_memory.c | 105 +++++++++++++++++++++++++++-------------------- mm/userfaultfd.c | 42 +++++++++++++++---- 2 files changed, 96 insertions(+), 51 deletions(-)