[v3,3/3] mm/hmm: Fix bad subpage pointer in try_to_unmap_one
diff mbox series

Message ID 20190724232700.23327-4-rcampbell@nvidia.com
State New
Headers show
Series
  • mm/hmm: fixes for device private page migration
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Commit Message

Ralph Campbell July 24, 2019, 11:27 p.m. UTC
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".

Fixes: a5430dda8a3a1c ("mm/migrate: support un-addressable ZONE_DEVICE page in migration")
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/rmap.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

Sasha Levin July 25, 2019, 2:03 a.m. UTC | #1
Hi,

[This is an automated email]

This commit has been processed because it contains a "Fixes:" tag,
fixing commit: a5430dda8a3a mm/migrate: support un-addressable ZONE_DEVICE page in migration.

The bot has tested the following trees: v5.2.2, v5.1.19, v4.19.60, v4.14.134.

v5.2.2: Build OK!
v5.1.19: Build OK!
v4.19.60: Build OK!
v4.14.134: Failed to apply! Possible dependencies:
    0f10851ea475 ("mm/mmu_notifier: avoid double notification when it is useless")


NOTE: The patch will not be queued to stable trees until it is upstream.

How should we proceed with this patch?

--
Thanks,
Sasha

Patch
diff mbox series

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;
 		}