linux-kernel - [PATCH 5.2 004/135] mm/hmm: fix bad subpage pointer in try_to_unmap

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Message-Id: <20190822170811.13303-5-sashal@kernel.org>
Date:   Thu, 22 Aug 2019 13:06:00 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ralph Campbell <rcampbell@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Jason Gunthorpe <jgg@...lanox.com>,
        John Hubbard <jhubbard@...dia.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Christoph Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...e.com>,
        Pekka Enberg <penberg@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH 5.2 004/135] mm/hmm: fix bad subpage pointer in try_to_unmap_one

From: Ralph Campbell <rcampbell@...dia.com>

commit 1de13ee59225dfc98d483f8cce7d83f97c0b31de upstream.

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@...dia.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 <rcampbell@...dia.com>
Cc: "Jérôme Glisse" <jglisse@...hat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Christoph Hellwig <hch@....de>
Cc: Jason Gunthorpe <jgg@...lanox.com>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Ira Weiny <ira.weiny@...el.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Logan Gunthorpe <logang@...tatee.com>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Pekka Enberg <penberg@...nel.org>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/rmap.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/rmap.c b/mm/rmap.c
index e5dfe2ae6b0d5..003377e242323 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;
 		}
 
-- 
2.20.1