1 files changed, 111 insertions, 1 deletions

diff --git a/arch/i386/mm/hugetlbpage.c b/arch/i386/mm/hugetlbpage.c
index 1719a8141f81..34728e4afe48 100644
--- a/arch/i386/mm/hugetlbpage.c
+++ b/arch/i386/mm/hugetlbpage.c
@@ -17,6 +17,113 @@
 #include <asm/tlb.h>
 #include <asm/tlbflush.h>
 
+static unsigned long page_table_shareable(struct vm_area_struct *svma,
+                                struct vm_area_struct *vma,
+                                unsigned long addr, pgoff_t idx)
+{
+        unsigned long saddr = ((idx - svma->vm_pgoff) << PAGE_SHIFT) +
+                                svma->vm_start;
+        unsigned long sbase = saddr & PUD_MASK;
+        unsigned long s_end = sbase + PUD_SIZE;
+
+        /*
+         * match the virtual addresses, permission and the alignment of the
+         * page table page.
+         */
+        if (pmd_index(addr) != pmd_index(saddr) ||
+            vma->vm_flags != svma->vm_flags ||
+            sbase < svma->vm_start || svma->vm_end < s_end)
+                return 0;
+
+        return saddr;
+}
+
+static int vma_shareable(struct vm_area_struct *vma, unsigned long addr)
+{
+        unsigned long base = addr & PUD_MASK;
+        unsigned long end = base + PUD_SIZE;
+
+        /*
+         * check on proper vm_flags and page table alignment
+         */
+        if (vma->vm_flags & VM_MAYSHARE &&
+            vma->vm_start <= base && end <= vma->vm_end)
+                return 1;
+        return 0;
+}
+
+/*
+ * search for a shareable pmd page for hugetlb.
+ */
+static void huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
+{
+        struct vm_area_struct *vma = find_vma(mm, addr);
+        struct address_space *mapping = vma->vm_file->f_mapping;
+        pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
+                        vma->vm_pgoff;
+        struct prio_tree_iter iter;
+        struct vm_area_struct *svma;
+        unsigned long saddr;
+        pte_t *spte = NULL;
+
+        if (!vma_shareable(vma, addr))
+                return;
+
+        spin_lock(&mapping->i_mmap_lock);
+        vma_prio_tree_foreach(svma, &iter, &mapping->i_mmap, idx, idx) {
+                if (svma == vma)
+                        continue;
+
+                saddr = page_table_shareable(svma, vma, addr, idx);
+                if (saddr) {
+                        spte = huge_pte_offset(svma->vm_mm, saddr);
+                        if (spte) {
+                                get_page(virt_to_page(spte));
+                                break;
+                        }
+                }
+        }
+
+        if (!spte)
+                goto out;
+
+        spin_lock(&mm->page_table_lock);
+        if (pud_none(*pud))
+                pud_populate(mm, pud, (unsigned long) spte & PAGE_MASK);
+        else
+                put_page(virt_to_page(spte));
+        spin_unlock(&mm->page_table_lock);
+out:
+        spin_unlock(&mapping->i_mmap_lock);
+}
+
+/*
+ * unmap huge page backed by shared pte.
+ *
+ * Hugetlb pte page is ref counted at the time of mapping.  If pte is shared
+ * indicated by page_count > 1, unmap is achieved by clearing pud and
+ * decrementing the ref count. If count == 1, the pte page is not shared.
+ *
+ * called with vma->vm_mm->page_table_lock held.
+ *
+ * returns: 1 successfully unmapped a shared pte page
+ *          0 the underlying pte page is not shared, or it is the last user
+ */
+int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
+{
+        pgd_t *pgd = pgd_offset(mm, *addr);
+        pud_t *pud = pud_offset(pgd, *addr);
+
+        BUG_ON(page_count(virt_to_page(ptep)) == 0);
+        if (page_count(virt_to_page(ptep)) == 1)
+                return 0;
+
+        pud_clear(pud);
+        put_page(virt_to_page(ptep));
+        *addr = ALIGN(*addr, HPAGE_SIZE * PTRS_PER_PTE) - HPAGE_SIZE;
+        return 1;
+}
+
 pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr)
 {
         pgd_t *pgd;
@@ -25,8 +132,11 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr)
 
         pgd = pgd_offset(mm, addr);
         pud = pud_alloc(mm, pgd, addr);
-        if (pud)
+        if (pud) {
+                if (pud_none(*pud))
+                        huge_pmd_share(mm, addr, pud);
                 pte = (pte_t *) pmd_alloc(mm, pud, addr);
+        }
         BUG_ON(pte && !pte_none(*pte) && !pte_huge(*pte));
 
         return pte;