linux-kernel - [PATCH v3 3/4] sparc64: Fix gup_huge

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Message-Id: <1497923621-96708-3-git-send-email-nitin.m.gupta@oracle.com>
Date:   Mon, 19 Jun 2017 18:53:00 -0700
From:   Nitin Gupta <nitin.m.gupta@...cle.com>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     Nitin Gupta <nitin.m.gupta@...cle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Lorenzo Stoakes <lstoakes@...il.com>, Jan Kara <jack@...e.cz>,
        Michal Hocko <mhocko@...e.com>, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 3/4] sparc64: Fix gup_huge_pmd

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.

Signed-off-by: Nitin Gupta <nitin.m.gupta@...cle.com>
---
 arch/sparc/mm/gup.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/sparc/mm/gup.c b/arch/sparc/mm/gup.c
index 7cfa9c5..b1c649d 100644
--- a/arch/sparc/mm/gup.c
+++ b/arch/sparc/mm/gup.c
@@ -80,6 +80,8 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
 	refs = 0;
 	head = pmd_page(pmd);
 	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+	if (PageTail(head))
+		head = compound_head(head);
 	do {
 		VM_BUG_ON(compound_head(page) != head);
 		pages[*nr] = page;
-- 
2.9.2