[PATCH 4.16 067/279] mm, pagemap: fix swap offset value for PMD migration entry

[Greg Kroah-Hartman]

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Huang Ying <ying.huang@xxxxxxxxx>

[ Upstream commit 88c28f2469151b031f8cea9b28ed5be1b74a4172 ]

The swap offset reported by /proc/<pid>/pagemap may be not correct for
PMD migration entries.  If addr passed into pagemap_pmd_range() isn't
aligned with PMD start address, the swap offset reported doesn't
reflect this.  And in the loop to report information of each sub-page,
the swap offset isn't increased accordingly as that for PFN.

This may happen after opening /proc/<pid>/pagemap and seeking to a page
whose address doesn't align with a PMD start address.  I have verified
this with a simple test program.

BTW: migration swap entries have PFN information, do we need to restrict
whether to show them?

[akpm@xxxxxxxxxxxxxxxxxxxx: fix typo, per Huang, Ying]
Link: http://lkml.kernel.org/r/20180408033737.10897-1-ying.huang@xxxxxxxxx
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrei Vagin <avagin@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: "Jerome Glisse" <jglisse@xxxxxxxxxx>
Cc: Daniel Colascione <dancol@xxxxxxxxxx>
Cc: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/proc/task_mmu.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1329,9 +1329,11 @@ static int pagemap_pmd_range(pmd_t *pmdp
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 		else if (is_swap_pmd(pmd)) {
 			swp_entry_t entry = pmd_to_swp_entry(pmd);
+			unsigned long offset = swp_offset(entry);
 
+			offset += (addr & ~PMD_MASK) >> PAGE_SHIFT;
 			frame = swp_type(entry) |
-				(swp_offset(entry) << MAX_SWAPFILES_SHIFT);
+				(offset << MAX_SWAPFILES_SHIFT);
 			flags |= PM_SWAP;
 			if (pmd_swp_soft_dirty(pmd))
 				flags |= PM_SOFT_DIRTY;
@@ -1351,6 +1353,8 @@ static int pagemap_pmd_range(pmd_t *pmdp
 				break;
 			if (pm->show_pfn && (flags & PM_PRESENT))
 				frame++;
+			else if (flags & PM_SWAP)
+				frame += (1 << MAX_SWAPFILES_SHIFT);
 		}
 		spin_unlock(ptl);
 		return err;