linux-kernel - [PATCH] hugetlb: handle write-protection faults in follow_hugetlb

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Message-Id: <20071206204152.16103.44490.stgit@kernel>
Date:	Thu, 06 Dec 2007 12:41:52 -0800
From:	Adam Litke <agl@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Adam Litke <agl@...ibm.com>, Dave Kleikamp <shaggy@...ibm.com>,
	Ken Chen <kenchen@...gle.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] hugetlb: handle write-protection faults in follow_hugetlb_page


The follow_hugetlb_page() fix I posted (merged as git commit
5b23dbe8173c212d6a326e35347b038705603d39) missed one case.  If the pte is
present, but not writable and write access is requested by the caller to
get_user_pages(), the code will do the wrong thing.  Rather than calling
hugetlb_fault to make the pte writable, it notes the presence of the pte
and continues.

This simple one-liner makes sure we also fault on the pte for this case.
Please apply.

Signed-off-by: Adam Litke <agl@...ibm.com>
Acked-by: Dave Kleikamp <shaggy@...ibm.com>
---

 mm/hugetlb.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6121b57..6f97821 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -907,7 +907,7 @@ int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		 */
 		pte = huge_pte_offset(mm, vaddr & HPAGE_MASK);
 
-		if (!pte || pte_none(*pte)) {
+		if (!pte || pte_none(*pte) || (write && !pte_write(*pte))) {
 			int ret;
 
 			spin_unlock(&mm->page_table_lock);
--
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