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

Sasha Levin
2019-05-07T05:47:32Z

From: Jan Kara <jack@suse.cz>

[ 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@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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
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