[PATCH AUTOSEL for 4.9 145/293] sparc64: Fix gup_huge_pmd

[Sasha Levin]

From: Nitin Gupta <nitin.m.gu...@oracle.com>

[ Upstream commit dbd2667a4fb9ce4f547982b07cd69dda127c47ea ]

The function assumes that each PMD points to head of a
huge page. This is not correct as a PMD can point to
start of any 8M region with a, say 256M, hugepage. The
fix ensures that it points to the correct head of any PMD
huge page.

Cc: Julian Calaby <julian.cal...@gmail.com>
Signed-off-by: Nitin Gupta <nitin.m.gu...@oracle.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
---
 arch/sparc/mm/gup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c
index cd0e32bbcb1d..f80cfc64c55b 100644
--- a/arch/sparc/mm/gup.c
+++ b/arch/sparc/mm/gup.c
@@ -78,8 +78,8 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long 
addr,
                return 0;
 
        refs = 0;
-       head = pmd_page(pmd);
-       page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+       page = pmd_page(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+       head = compound_head(page);
        do {
                VM_BUG_ON(compound_head(page) != head);
                pages[*nr] = page;
-- 
2.15.1