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From:   Ralph Campbell <rcampbell@nvidia.com>
To:     <linux-mm@kvack.org>
CC:     <linux-kernel@vger.kernel.org>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= <jglisse@redhat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Kravetz <mike.kravetz@oracle.com>
Subject: [PATCH] mm/hmm: Fix bad subpage pointer in try_to_unmap_one
Date:   Tue, 9 Jul 2019 15:35:56 -0700
Message-ID: <20190709223556.28908-1-rcampbell@nvidia.com>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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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().

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "J=C3=A9r=C3=B4me Glisse" <jglisse@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
---
 mm/rmap.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/rmap.c b/mm/rmap.c
index e5dfe2ae6b0d..ec1af8b60423 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1476,6 +1476,7 @@ static bool try_to_unmap_one(struct page *page, struc=
t vm_area_struct *vma,
 			 * No need to invalidate here it will synchronize on
 			 * against the special swap migration pte.
 			 */
+			subpage =3D page;
 			goto discard;
 		}
=20
--=20
2.20.1