mm/follow_page_mask: split follow_page_mask to smaller functions.

Makes code reading easy.  No functional changes in this patch.  In a
followup patch, we will be updating the follow_page_mask to handle
hugetlb hugepd format so that archs like ppc64 can switch to the generic
version.  This split helps in doing that nicely.

Link: http://lkml.kernel.org/r/1494926612-23928-3-git-send-email-aneesh.kumar@linux.vnet.ibm.com
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Mike Kravetz <kravetz@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 91 insertions, 57 deletions

diff --git a/mm/gup.c b/mm/gup.c
index 3ab78dc3db7d..bf68e21d7a3a 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -208,68 +208,16 @@ no_page:
         return no_page_table(vma, flags);
 }
 
-/**
- * follow_page_mask - look up a page descriptor from a user-virtual address
- * @vma: vm_area_struct mapping @address
- * @address: virtual address to look up
- * @flags: flags modifying lookup behaviour
- * @page_mask: on output, *page_mask is set according to the size of the page
- *
- * @flags can have FOLL_ flags set, defined in <linux/mm.h>
- *
- * Returns the mapped (struct page *), %NULL if no mapping exists, or
- * an error pointer if there is a mapping to something not represented
- * by a page descriptor (see also vm_normal_page()).
- */
-struct page *follow_page_mask(struct vm_area_struct *vma,
-                              unsigned long address, unsigned int flags,
-                              unsigned int *page_mask)
+static struct page *follow_pmd_mask(struct vm_area_struct *vma,
+                                    unsigned long address, pud_t *pudp,
+                                    unsigned int flags, unsigned int *page_mask)
 {
-        pgd_t *pgd;
-        p4d_t *p4d;
-        pud_t *pud;
         pmd_t *pmd;
         spinlock_t *ptl;
         struct page *page;
         struct mm_struct *mm = vma->vm_mm;
 
-        *page_mask = 0;
-
-        page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
-        if (!IS_ERR(page)) {
-                BUG_ON(flags & FOLL_GET);
-                return page;
-        }
-
-        pgd = pgd_offset(mm, address);
-        if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
-                return no_page_table(vma, flags);
-        p4d = p4d_offset(pgd, address);
-        if (p4d_none(*p4d))
-                return no_page_table(vma, flags);
-        BUILD_BUG_ON(p4d_huge(*p4d));
-        if (unlikely(p4d_bad(*p4d)))
-                return no_page_table(vma, flags);
-        pud = pud_offset(p4d, address);
-        if (pud_none(*pud))
-                return no_page_table(vma, flags);
-        if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
-                page = follow_huge_pud(mm, address, pud, flags);
-                if (page)
-                        return page;
-                return no_page_table(vma, flags);
-        }
-        if (pud_devmap(*pud)) {
-                ptl = pud_lock(mm, pud);
-                page = follow_devmap_pud(vma, address, pud, flags);
-                spin_unlock(ptl);
-                if (page)
-                        return page;
-        }
-        if (unlikely(pud_bad(*pud)))
-                return no_page_table(vma, flags);
-
-        pmd = pmd_offset(pud, address);
+        pmd = pmd_offset(pudp, address);
         if (pmd_none(*pmd))
                 return no_page_table(vma, flags);
         if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
@@ -319,13 +267,99 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
                 return ret ? ERR_PTR(ret) :
                         follow_page_pte(vma, address, pmd, flags);
         }
-
         page = follow_trans_huge_pmd(vma, address, pmd, flags);
         spin_unlock(ptl);
         *page_mask = HPAGE_PMD_NR - 1;
         return page;
 }
 
+
+static struct page *follow_pud_mask(struct vm_area_struct *vma,
+                                    unsigned long address, p4d_t *p4dp,
+                                    unsigned int flags, unsigned int *page_mask)
+{
+        pud_t *pud;
+        spinlock_t *ptl;
+        struct page *page;
+        struct mm_struct *mm = vma->vm_mm;
+
+        pud = pud_offset(p4dp, address);
+        if (pud_none(*pud))
+                return no_page_table(vma, flags);
+        if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
+                page = follow_huge_pud(mm, address, pud, flags);
+                if (page)
+                        return page;
+                return no_page_table(vma, flags);
+        }
+        if (pud_devmap(*pud)) {
+                ptl = pud_lock(mm, pud);
+                page = follow_devmap_pud(vma, address, pud, flags);
+                spin_unlock(ptl);
+                if (page)
+                        return page;
+        }
+        if (unlikely(pud_bad(*pud)))
+                return no_page_table(vma, flags);
+
+        return follow_pmd_mask(vma, address, pud, flags, page_mask);
+}
+
+
+static struct page *follow_p4d_mask(struct vm_area_struct *vma,
+                                    unsigned long address, pgd_t *pgdp,
+                                    unsigned int flags, unsigned int *page_mask)
+{
+        p4d_t *p4d;
+
+        p4d = p4d_offset(pgdp, address);
+        if (p4d_none(*p4d))
+                return no_page_table(vma, flags);
+        BUILD_BUG_ON(p4d_huge(*p4d));
+        if (unlikely(p4d_bad(*p4d)))
+                return no_page_table(vma, flags);
+
+        return follow_pud_mask(vma, address, p4d, flags, page_mask);
+}
+
+/**
+ * follow_page_mask - look up a page descriptor from a user-virtual address
+ * @vma: vm_area_struct mapping @address
+ * @address: virtual address to look up
+ * @flags: flags modifying lookup behaviour
+ * @page_mask: on output, *page_mask is set according to the size of the page
+ *
+ * @flags can have FOLL_ flags set, defined in <linux/mm.h>
+ *
+ * Returns the mapped (struct page *), %NULL if no mapping exists, or
+ * an error pointer if there is a mapping to something not represented
+ * by a page descriptor (see also vm_normal_page()).
+ */
+struct page *follow_page_mask(struct vm_area_struct *vma,
+                              unsigned long address, unsigned int flags,
+                              unsigned int *page_mask)
+{
+        pgd_t *pgd;
+        struct page *page;
+        struct mm_struct *mm = vma->vm_mm;
+
+        *page_mask = 0;
+
+        /* make this handle hugepd */
+        page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
+        if (!IS_ERR(page)) {
+                BUG_ON(flags & FOLL_GET);
+                return page;
+        }
+
+        pgd = pgd_offset(mm, address);
+
+        if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+                return no_page_table(vma, flags);
+
+        return follow_p4d_mask(vma, address, pgd, flags, page_mask);
+}
+
 static int get_gate_page(struct mm_struct *mm, unsigned long address,
                 unsigned int gup_flags, struct vm_area_struct **vma,
                 struct page **page)