[PATCH AUTOSEL 4.14 86/95] mm/memory.c: fix modifying of page protection by insert_pfn()

[Sasha Levin]

From: Jan Kara <jack@xxxxxxx>

[ Upstream commit cae85cb8add35f678cf487139d05e083ce2f570a ]

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@xxxxxxx
Fixes: b2770da64254 "mm: add vm_insert_mixed_mkwrite()"
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reported-by: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Chandan Rajendra <chandan@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 mm/memory.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index f99b64ca1303..e9bce27bc18c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1813,10 +1813,12 @@ static int 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.. */
@@ -1825,7 +1827,6 @@ static int 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);
-- 
2.20.1