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authorJohannes Weiner <hannes@cmpxchg.org>2009-06-16 15:32:33 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-06-16 19:47:39 -0700
commitf8ad0f499fad5cdbcaaa2d97542b2db869b5a770 (patch)
treef1b5e91072238c2a303940bd522485484dc22105
parente9bb35df6f813ca46f8e6273add657643c7df73f (diff)
mm: introduce follow_pte()
A generic readonly page table lookup helper to map an address space and an address from it to a pte. Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Christoph Hellwig <hch@infradead.org> Acked-by: Magnus Damm <magnus.damm@gmail.com> Cc: Hans Verkuil <hverkuil@xs4all.nl> Cc: Paul Mundt <lethal@linux-sh.org> Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/memory.c37
1 files changed, 37 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 891bad0613f..7135d6b2599 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3103,6 +3103,43 @@ int in_gate_area_no_task(unsigned long addr)
#endif /* __HAVE_ARCH_GATE_AREA */
+static int follow_pte(struct mm_struct *mm, unsigned long address,
+ pte_t **ptepp, spinlock_t **ptlp)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *ptep;
+
+ pgd = pgd_offset(mm, address);
+ if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+ goto out;
+
+ pud = pud_offset(pgd, address);
+ if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+ goto out;
+
+ pmd = pmd_offset(pud, address);
+ if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+ goto out;
+
+ /* We cannot handle huge page PFN maps. Luckily they don't exist. */
+ if (pmd_huge(*pmd))
+ goto out;
+
+ ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
+ if (!ptep)
+ goto out;
+ if (!pte_present(*ptep))
+ goto unlock;
+ *ptepp = ptep;
+ return 0;
+unlock:
+ pte_unmap_unlock(ptep, *ptlp);
+out:
+ return -EINVAL;
+}
+
#ifdef CONFIG_HAVE_IOREMAP_PROT
int follow_phys(struct vm_area_struct *vma,
unsigned long address, unsigned int flags,