From 1de13ee59225dfc98d483f8cce7d83f97c0b31de Mon Sep 17 00:00:00 2001 From: Ralph Campbell Date: Tue, 13 Aug 2019 15:37:11 -0700 Subject: mm/hmm: fix bad subpage pointer in try_to_unmap_one MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When migrating an anonymous private page to a ZONE_DEVICE private page, the source page->mapping and page->index fields are copied to the destination ZONE_DEVICE struct page and the page_mapcount() is increased. This is so rmap_walk() can be used to unmap and migrate the page back to system memory. However, try_to_unmap_one() computes the subpage pointer from a swap pte which computes an invalid page pointer and a kernel panic results such as: BUG: unable to handle page fault for address: ffffea1fffffffc8 Currently, only single pages can be migrated to device private memory so no subpage computation is needed and it can be set to "page". [rcampbell@nvidia.com: add comment] Link: http://lkml.kernel.org/r/20190724232700.23327-4-rcampbell@nvidia.com Link: http://lkml.kernel.org/r/20190719192955.30462-4-rcampbell@nvidia.com Fixes: a5430dda8a3a1c ("mm/migrate: support un-addressable ZONE_DEVICE page in migration") Signed-off-by: Ralph Campbell Cc: "Jérôme Glisse" Cc: "Kirill A. Shutemov" Cc: Mike Kravetz Cc: Christoph Hellwig Cc: Jason Gunthorpe Cc: John Hubbard Cc: Andrea Arcangeli Cc: Andrey Ryabinin Cc: Christoph Lameter Cc: Dan Williams Cc: Dave Hansen Cc: Ira Weiny Cc: Jan Kara Cc: Lai Jiangshan Cc: Logan Gunthorpe Cc: Martin Schwidefsky Cc: Matthew Wilcox Cc: Mel Gorman Cc: Michal Hocko Cc: Pekka Enberg Cc: Randy Dunlap Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/rmap.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'mm/rmap.c') diff --git a/mm/rmap.c b/mm/rmap.c index e5dfe2ae6b0d..003377e24232 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1475,7 +1475,15 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, /* * No need to invalidate here it will synchronize on * against the special swap migration pte. + * + * The assignment to subpage above was computed from a + * swap PTE which results in an invalid pointer. + * Since only PAGE_SIZE pages can currently be + * migrated, just set it to page. This will need to be + * changed when hugepage migrations to device private + * memory are supported. */ + subpage = page; goto discard; } -- cgit v1.2.3-59-g8ed1b