[PATCH v2 05/11] mm: add follow_pte_pmd()

[Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>]

Similar to follow_pte(), follow_pte_pmd() allows either a PTE leaf or a
huge page PMD leaf to be found and returned.

Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---
 include/linux/mm.h |  2 ++
 mm/memory.c        | 38 ++++++++++++++++++++++++++++++--------
 2 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 80001de..393441c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1166,6 +1166,8 @@ int copy_page_range(struct mm_struct *dst, struct 
mm_struct *src,
                        struct vm_area_struct *vma);
 void unmap_mapping_range(struct address_space *mapping,
                loff_t const holebegin, loff_t const holelen, int even_cows);
+int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+                            pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp);
 int follow_pfn(struct vm_area_struct *vma, unsigned long address,
        unsigned long *pfn);
 int follow_phys(struct vm_area_struct *vma, unsigned long address,
diff --git a/mm/memory.c b/mm/memory.c
index deb679c..7f4090e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3512,8 +3512,8 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, 
unsigned long address)
 }
 #endif /* __PAGETABLE_PMD_FOLDED */
 
-static int __follow_pte(struct mm_struct *mm, unsigned long address,
-               pte_t **ptepp, spinlock_t **ptlp)
+static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+               pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
 {
        pgd_t *pgd;
        pud_t *pud;
@@ -3529,12 +3529,20 @@ static int __follow_pte(struct mm_struct *mm, unsigned 
long address,
                goto out;
 
        pmd = pmd_offset(pud, address);
-       VM_BUG_ON(pmd_trans_huge(*pmd));
-       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))
+       if (pmd_huge(*pmd)) {
+               if (!pmdpp)
+                       goto out;
+
+               *ptlp = pmd_lock(mm, pmd);
+               if (pmd_huge(*pmd)) {
+                       *pmdpp = pmd;
+                       return 0;
+               }
+               spin_unlock(*ptlp);
+       }
+
+       if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
                goto out;
 
        ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
@@ -3557,9 +3565,23 @@ static inline int follow_pte(struct mm_struct *mm, 
unsigned long address,
 
        /* (void) is needed to make gcc happy */
        (void) __cond_lock(*ptlp,
-                          !(res = __follow_pte(mm, address, ptepp, ptlp)));
+                          !(res = __follow_pte_pmd(mm, address, ptepp, NULL,
+                                          ptlp)));
+       return res;
+}
+
+int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+                            pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
+{
+       int res;
+
+       /* (void) is needed to make gcc happy */
+       (void) __cond_lock(*ptlp,
+                          !(res = __follow_pte_pmd(mm, address, ptepp, pmdpp,
+                                          ptlp)));
        return res;
 }
+EXPORT_SYMBOL(follow_pte_pmd);
 
 /**
  * follow_pfn - look up PFN at a user virtual address
-- 
2.1.0