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b=lg0faUOH1V2wnG1sZ9vb4NLoeob+zf4y9+6E6/TzmuyfTmt/E1jMYKFAvObI7K60Q6DNhn 2augVta472Bi0jcUUPCrhDi2ixvVl1lk6qe0f7o3sF1voMWPkfnIW/1zHGNYd05YF56chL 6oaBgQ6q6K7DG0rGLvD6R3Hz0xT1m7U= Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=Gk7z9Pyo; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf11.hostedemail.com: domain of huang.ying.caritas@gmail.com designates 209.85.216.46 as permitted sender) smtp.mailfrom=huang.ying.caritas@gmail.com X-Rspam-User: X-Stat-Signature: 41i1c1c33i74cjryjafn3khbizsmx68g X-Rspamd-Queue-Id: B25D3401C4 X-Rspamd-Server: rspam11 X-HE-Tag: 1660637443-156438 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Aug 16, 2022 at 3:39 PM Alistair Popple wrote: > > migrate_vma_setup() has a fast path in migrate_vma_collect_pmd() that > installs migration entries directly if it can lock the migrating page. > When removing a dirty pte the dirty bit is supposed to be carried over > to the underlying page to prevent it being lost. > > Currently migrate_vma_*() can only be used for private anonymous > mappings. That means loss of the dirty bit usually doesn't result in > data loss because these pages are typically not file-backed. However > pages may be backed by swap storage which can result in data loss if an > attempt is made to migrate a dirty page that doesn't yet have the > PageDirty flag set. > > In this case migration will fail due to unexpected references but the > dirty pte bit will be lost. If the page is subsequently reclaimed data > won't be written back to swap storage as it is considered uptodate, > resulting in data loss if the page is subsequently accessed. > > Prevent this by copying the dirty bit to the page when removing the pte > to match what try_to_migrate_one() does. > > Signed-off-by: Alistair Popple > Acked-by: Peter Xu > Reported-by: Huang Ying > Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages") > Cc: stable@vger.kernel.org > > --- > > Changes for v2: > > - Fixed up Reported-by tag. > - Added Peter's Acked-by. > - Atomically read and clear the pte to prevent the dirty bit getting > set after reading it. > - Added fixes tag > --- > mm/migrate_device.c | 21 ++++++++------------- > 1 file changed, 8 insertions(+), 13 deletions(-) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index 27fb37d..e2d09e5 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -7,6 +7,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -61,7 +62,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > struct migrate_vma *migrate = walk->private; > struct vm_area_struct *vma = walk->vma; > struct mm_struct *mm = vma->vm_mm; > - unsigned long addr = start, unmapped = 0; > + unsigned long addr = start; > spinlock_t *ptl; > pte_t *ptep; > > @@ -193,11 +194,10 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > bool anon_exclusive; > pte_t swp_pte; > > + flush_cache_page(vma, addr, pte_pfn(*ptep)); > + pte = ptep_clear_flush(vma, addr, ptep); Although I think it's possible to batch the TLB flushing just before unlocking PTL. The current code looks correct. Reviewed-by: "Huang, Ying" Best Regards, Huang, Ying > anon_exclusive = PageAnon(page) && PageAnonExclusive(page); > if (anon_exclusive) { > - flush_cache_page(vma, addr, pte_pfn(*ptep)); > - ptep_clear_flush(vma, addr, ptep); > - > if (page_try_share_anon_rmap(page)) { > set_pte_at(mm, addr, ptep, pte); > unlock_page(page); > @@ -205,12 +205,14 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > mpfn = 0; > goto next; > } > - } else { > - ptep_get_and_clear(mm, addr, ptep); > } > > migrate->cpages++; > > + /* Set the dirty flag on the folio now the pte is gone. */ > + if (pte_dirty(pte)) > + folio_mark_dirty(page_folio(page)); > + > /* Setup special migration page table entry */ > if (mpfn & MIGRATE_PFN_WRITE) > entry = make_writable_migration_entry( > @@ -242,9 +244,6 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > */ > page_remove_rmap(page, vma, false); > put_page(page); > - > - if (pte_present(pte)) > - unmapped++; > } else { > put_page(page); > mpfn = 0; > @@ -257,10 +256,6 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > arch_leave_lazy_mmu_mode(); > pte_unmap_unlock(ptep - 1, ptl); > > - /* Only flush the TLB if we actually modified any entries */ > - if (unmapped) > - flush_tlb_range(walk->vma, start, end); > - > return 0; > } > > > base-commit: ffcf9c5700e49c0aee42dcba9a12ba21338e8136 > -- > git-series 0.9.1 >