mm: add follow_pte_pmd()

Patch series "Write protect DAX PMDs in *sync path".

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, as detailed in patch 2.

This series is based on Dan's "libnvdimm-pending" branch, which is the
current home for Jan's "dax: Page invalidation fixes" series.  You can
find a working tree here:

  https://git.kernel.org/cgit/linux/kernel/git/zwisler/linux.git/log/?h=dax_pmd_clean

This patch (of 2):

Similar to follow_pte(), follow_pte_pmd() allows either a PTE leaf or a
huge page PMD leaf to be found and returned.

Link: http://lkml.kernel.org/r/1482272586-21177-2-git-send-email-ross.zwisler@linux.intel.com
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index fe6b4036664a9a7c82fe4a22be93288928eceac1..02793ac64ac626a7d6f3cd13cef0f9a875c3f723 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1212,6 +1212,8 @@ void unmap_mapping_range(struct address_space *mapping,
                loff_t const holebegin, loff_t const holelen, int even_cows);
 int follow_pte(struct mm_struct *mm, unsigned long address, pte_t **ptepp,
               spinlock_t **ptlp);
+int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+                            pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp);
 int follow_pfn(struct vm_area_struct *vma, unsigned long address,
        unsigned long *pfn);
 int follow_phys(struct vm_area_struct *vma, unsigned long address,

diff --git a/mm/memory.c b/mm/memory.c
index 9f2c15cdb32c6327c0d2e8992c5c269ba573f698..b62f3bc63481b8a32c7157fca0e334dbdd1b7ebc 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3772,8 +3772,8 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
 }
 #endif /* __PAGETABLE_PMD_FOLDED */
 
-static int __follow_pte(struct mm_struct *mm, unsigned long address,
-               pte_t **ptepp, spinlock_t **ptlp)
+static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+               pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
 {
        pgd_t *pgd;
        pud_t *pud;
@@ -3790,11 +3790,20 @@ static int __follow_pte(struct mm_struct *mm, unsigned long address,
 
        pmd = pmd_offset(pud, address);
        VM_BUG_ON(pmd_trans_huge(*pmd));
-       if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
-               goto out;
 
-       /* We cannot handle huge page PFN maps. Luckily they don't exist. */
-       if (pmd_huge(*pmd))
+       if (pmd_huge(*pmd)) {
+               if (!pmdpp)
+                       goto out;
+
+               *ptlp = pmd_lock(mm, pmd);
+               if (pmd_huge(*pmd)) {
+                       *pmdpp = pmd;
+                       return 0;
+               }
+               spin_unlock(*ptlp);
+       }
+
+       if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
                goto out;
 
        ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
@@ -3817,9 +3826,23 @@ int follow_pte(struct mm_struct *mm, unsigned long address, pte_t **ptepp,
 
        /* (void) is needed to make gcc happy */
        (void) __cond_lock(*ptlp,
-                          !(res = __follow_pte(mm, address, ptepp, ptlp)));
+                          !(res = __follow_pte_pmd(mm, address, ptepp, NULL,
+                                          ptlp)));
+       return res;
+}
+
+int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+                            pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
+{
+       int res;
+
+       /* (void) is needed to make gcc happy */
+       (void) __cond_lock(*ptlp,
+                          !(res = __follow_pte_pmd(mm, address, ptepp, pmdpp,
+                                          ptlp)));
        return res;
 }
+EXPORT_SYMBOL(follow_pte_pmd);
 
 /**
  * follow_pfn - look up PFN at a user virtual address