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@xxxxxxxxxxx>
---
mm/memory.c | 37 +++++++++++++++++++++++++++++++++++++
1 files changed, 37 insertions(+), 0 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index cf6873e..a621319 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3009,6 +3009,43 @@ 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,
--
1.6.2.1.135.gde769
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