[patch 02/22] mm/memory.c: fix modifying of page protection by insert_pfn()

[patch 02/22] mm/memory.c: fix modifying of page protection by insert_pfn()

[akpm]

From: Jan Kara <jack@suse.cz>
Subject: mm/memory.c: fix modifying of page protection by insert_pfn()

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

[c00000000007610c] set_pte_at+0x3c/0x190
LR [c000000000378628] insert_pfn+0x208/0x280
Call Trace:
[c0000002125df980] [8000000000000104] 0x8000000000000104 (unreliable)
[c0000002125df9c0] [c000000000378488] insert_pfn+0x68/0x280
[c0000002125dfa30] [c0000000004a5494] dax_iomap_pte_fault.isra.7+0x734/0xa40
[c0000002125dfb50] [c000000000627250] __xfs_filemap_fault+0x280/0x2d0
[c0000002125dfbb0] [c000000000373abc] do_wp_page+0x48c/0xa40
[c0000002125dfc00] [c000000000379170] __handle_mm_fault+0x8d0/0x1fd0
[c0000002125dfd00] [c00000000037a9b0] handle_mm_fault+0x140/0x250
[c0000002125dfd40] [c000000000074bb0] __do_page_fault+0x300/0xd60
[c0000002125dfe20] [c00000000000acf4] 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>
---

 mm/memory.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/mm/memory.c~mm-fix-modifying-of-page-protection-by-insert_pfn
+++ a/mm/memory.c
@@ -1549,10 +1549,12 @@ static vm_fault_t insert_pfn(struct vm_a
 				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_a
 	else
 		entry = pte_mkspecial(pfn_t_pte(pfn, prot));
 
-out_mkwrite:
 	if (mkwrite) {
 		entry = pte_mkyoung(entry);
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
_