Re: [PATCH] mm/hmm: Fix bad subpage pointer in try_to_unmap_one

[Andrew Morton]

On Tue, 9 Jul 2019 18:24:57 -0700 Ralph Campbell <rcampbell@xxxxxxxxxx> wrote:

> 
> On 7/9/19 5:28 PM, Andrew Morton wrote:
> > On Tue, 9 Jul 2019 15:35:56 -0700 Ralph Campbell <rcampbell@xxxxxxxxxx> wrote:
> > 
> >> When migrating a ZONE device private page from device memory to system
> >> memory, the subpage pointer is initialized from a swap pte which computes
> >> an invalid page pointer. A kernel panic results such as:
> >>
> >> BUG: unable to handle page fault for address: ffffea1fffffffc8
> >>
> >> Initialize subpage correctly before calling page_remove_rmap().
> > 
> > I think this is
> > 
> > Fixes:  a5430dda8a3a1c ("mm/migrate: support un-addressable ZONE_DEVICE page in migration")
> > Cc: stable
> > 
> > yes?
> > 
> 
> Yes. Can you add this or should I send a v2?

I updated the patch.  Could we please have some review input?


From: Ralph Campbell <rcampbell@xxxxxxxxxx>
Subject: mm/hmm: fix bad subpage pointer in try_to_unmap_one

When migrating a ZONE device private page from device memory to system
memory, the subpage pointer is initialized from a swap pte which computes
an invalid page pointer. A kernel panic results such as:

BUG: unable to handle page fault for address: ffffea1fffffffc8

Initialize subpage correctly before calling page_remove_rmap().

Link: http://lkml.kernel.org/r/20190709223556.28908-1-rcampbell@xxxxxxxxxx
Fixes: a5430dda8a3a1c ("mm/migrate: support un-addressable ZONE_DEVICE page in migration")
Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: "Jérôme Glisse" <jglisse@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/rmap.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/rmap.c~mm-hmm-fix-bad-subpage-pointer-in-try_to_unmap_one
+++ a/mm/rmap.c
@@ -1476,6 +1476,7 @@ static bool try_to_unmap_one(struct page
 			 * No need to invalidate here it will synchronize on
 			 * against the special swap migration pte.
 			 */
+			subpage = page;
 			goto discard;
 		}
 
_