From f729c8c9b24f0540a6e6b86e68f3888ba90ef7e7 Mon Sep 17 00:00:00 2001 From: Ross Zwisler Date: Tue, 10 Jan 2017 16:57:24 -0800 Subject: dax: wrprotect pmd_t in dax_mapping_entry_mkclean Currently dax_mapping_entry_mkclean() fails to clean and write protect the pmd_t of a DAX PMD entry during an *sync operation. This can result in data loss in the following sequence: 1) mmap write to DAX PMD, dirtying PMD radix tree entry and making the pmd_t dirty and writeable 2) fsync, flushing out PMD data and cleaning the radix tree entry. We currently fail to mark the pmd_t as clean and write protected. 3) more mmap writes to the PMD. These don't cause any page faults since the pmd_t is dirty and writeable. The radix tree entry remains clean. 4) fsync, which fails to flush the dirty PMD data because the radix tree entry was clean. 5) crash - dirty data that should have been fsync'd as part of 4) could still have been in the processor cache, and is lost. Fix this by marking the pmd_t clean and write protected in dax_mapping_entry_mkclean(), which is called as part of the fsync operation 2). This will cause the writes in step 3) above to generate page faults where we'll re-dirty the PMD radix tree entry, resulting in flushes in the fsync that happens in step 4). Fixes: 4b4bb46d00b3 ("dax: clear dirty entry tags on cache flush") Link: http://lkml.kernel.org/r/1482272586-21177-3-git-send-email-ross.zwisler@linux.intel.com Signed-off-by: Ross Zwisler Reviewed-by: Jan Kara Cc: Alexander Viro Cc: Christoph Hellwig Cc: Dan Williams Cc: Dave Chinner Cc: Jan Kara Cc: Matthew Wilcox Cc: Dave Hansen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/dax.c | 51 ++++++++++++++++++++++++++++++++++++--------------- 1 file changed, 36 insertions(+), 15 deletions(-) (limited to 'fs/dax.c') diff --git a/fs/dax.c b/fs/dax.c index 5c74f60d0a50..ddcddfeaa03b 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -691,8 +691,8 @@ static void dax_mapping_entry_mkclean(struct address_space *mapping, pgoff_t index, unsigned long pfn) { struct vm_area_struct *vma; - pte_t *ptep; - pte_t pte; + pte_t pte, *ptep = NULL; + pmd_t *pmdp = NULL; spinlock_t *ptl; bool changed; @@ -707,21 +707,42 @@ static void dax_mapping_entry_mkclean(struct address_space *mapping, address = pgoff_address(index, vma); changed = false; - if (follow_pte(vma->vm_mm, address, &ptep, &ptl)) + if (follow_pte_pmd(vma->vm_mm, address, &ptep, &pmdp, &ptl)) continue; - if (pfn != pte_pfn(*ptep)) - goto unlock; - if (!pte_dirty(*ptep) && !pte_write(*ptep)) - goto unlock; - flush_cache_page(vma, address, pfn); - pte = ptep_clear_flush(vma, address, ptep); - pte = pte_wrprotect(pte); - pte = pte_mkclean(pte); - set_pte_at(vma->vm_mm, address, ptep, pte); - changed = true; -unlock: - pte_unmap_unlock(ptep, ptl); + if (pmdp) { +#ifdef CONFIG_FS_DAX_PMD + pmd_t pmd; + + if (pfn != pmd_pfn(*pmdp)) + goto unlock_pmd; + if (!pmd_dirty(*pmdp) && !pmd_write(*pmdp)) + goto unlock_pmd; + + flush_cache_page(vma, address, pfn); + pmd = pmdp_huge_clear_flush(vma, address, pmdp); + pmd = pmd_wrprotect(pmd); + pmd = pmd_mkclean(pmd); + set_pmd_at(vma->vm_mm, address, pmdp, pmd); + changed = true; +unlock_pmd: + spin_unlock(ptl); +#endif + } else { + if (pfn != pte_pfn(*ptep)) + goto unlock_pte; + if (!pte_dirty(*ptep) && !pte_write(*ptep)) + goto unlock_pte; + + flush_cache_page(vma, address, pfn); + pte = ptep_clear_flush(vma, address, ptep); + pte = pte_wrprotect(pte); + pte = pte_mkclean(pte); + set_pte_at(vma->vm_mm, address, ptep, pte); + changed = true; +unlock_pte: + pte_unmap_unlock(ptep, ptl); + } if (changed) mmu_notifier_invalidate_page(vma->vm_mm, address); -- cgit v1.2.3-55-g7522