linux-kernel - [PATCH 09/10] mm: numa: Add paranoid check around pte_protnone

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Date:	Thu,  4 Dec 2014 11:24:32 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Hugh Dickins <hughd@...gle.com>, Dave Jones <davej@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LinuxPPC-dev <linuxppc-dev@...ts.ozlabs.org>,
	Mel Gorman <mgorman@...e.de>
Subject: [PATCH 09/10] mm: numa: Add paranoid check around pte_protnone_numa

pte_protnone_numa is only safe to use after VMA checks for PROT_NONE are
complete. Treating a real PROT_NONE PTE as a NUMA hinting fault is going
to result in strangeness so add a check for it. BUG_ON looks like overkill
but if this is hit then it's a serious bug that could result in corruption
so do not even try recovering. It would have been more comprehensive to
check VMA flags in pte_protnone_numa but it would have made the API ugly
just for a debugging check.

Signed-off-by: Mel Gorman <mgorman@...e.de>
---
 mm/huge_memory.c | 3 +++
 mm/memory.c      | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ad2a3ee..8546654 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1273,6 +1273,9 @@ int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	bool migrated = false;
 	int flags = 0;
 
+	/* A PROT_NONE fault should not end up here */
+	BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
+
 	ptl = pmd_lock(mm, pmdp);
 	if (unlikely(!pmd_same(pmd, *pmdp)))
 		goto out_unlock;
diff --git a/mm/memory.c b/mm/memory.c
index 2ec07a9..7d97af5 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3109,6 +3109,9 @@ static int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	bool migrated = false;
 	int flags = 0;
 
+	/* A PROT_NONE fault should not end up here */
+	BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
+
 	/*
 	* The "pte" at this point cannot be used safely without
 	* validation through pte_unmap_same(). It's of NUMA type but
-- 
2.1.2

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