mm/memory.c: fix modifying of page protection by insert_pfn()

Aneesh has reported that PPC triggers the following warning when
excercising DAX code:

  IP set_pte_at+0x3c/0x190
  LR insert_pfn+0x208/0x280
  Call Trace:
     insert_pfn+0x68/0x280
     dax_iomap_pte_fault.isra.7+0x734/0xa40
     __xfs_filemap_fault+0x280/0x2d0
     do_wp_page+0x48c/0xa40
     __handle_mm_fault+0x8d0/0x1fd0
     handle_mm_fault+0x140/0x250
     __do_page_fault+0x300/0xd60
     handle_page_fault+0x18

Now that is WARN_ON in set_pte_at which is

        VM_WARN_ON(pte_hw_valid(*ptep) && !pte_protnone(*ptep));

The problem is that on some architectures set_pte_at() cannot cope with
a situation where there is already some (different) valid entry present.

Use ptep_set_access_flags() instead to modify the pfn which is built to
deal with modifying existing PTE.

Link: http://lkml.kernel.org/r/20190311084537.16029-1-jack@suse.cz
Fixes: b2770da64254 "mm: add vm_insert_mixed_mkwrite()"
Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Cc: Chandan Rajendra <chandan@linux.ibm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index 47fe250..ab650c2 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1549,10 +1549,12 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
                                WARN_ON_ONCE(!is_zero_pfn(pte_pfn(*pte)));
                                goto out_unlock;
                        }
-                       entry = *pte;
-                       goto out_mkwrite;
-               } else
-                       goto out_unlock;
+                       entry = pte_mkyoung(*pte);
+                       entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+                       if (ptep_set_access_flags(vma, addr, pte, entry, 1))
+                               update_mmu_cache(vma, addr, pte);
+               }
+               goto out_unlock;
        }
 
        /* Ok, finally just insert the thing.. */
@@ -1561,7 +1563,6 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
        else
                entry = pte_mkspecial(pfn_t_pte(pfn, prot));
 
-out_mkwrite:
        if (mkwrite) {
                entry = pte_mkyoung(entry);
                entry = maybe_mkwrite(pte_mkdirty(entry), vma);