2 files changed, 70 insertions, 17 deletions

diff --git a/Documentation/nommu-mmap.txt b/Documentation/nommu-mmap.txt
index 83f4b083d57e..3ce890664936 100644
--- a/Documentation/nommu-mmap.txt
+++ b/Documentation/nommu-mmap.txt
@@ -128,6 +128,30 @@ FURTHER NOTES ON NO-MMU MMAP
      error will result if they don't. This is most likely to be encountered
      with character device files, pipes, fifos and sockets.
 
+
+=============
+NO-MMU MREMAP
+=============
+
+The mremap() function is partially supported.  It may change the size of a
+mapping, and may move it[*] if MREMAP_MAYMOVE is specified and if the new size
+of the mapping exceeds the size of the slab object currently occupied by the
+memory to which the mapping refers, or if a smaller slab object could be used.
+
+MREMAP_FIXED is not supported, though it is ignored if there's no change of
+address and the object does not need to be moved.
+
+Shared mappings may not be moved.  Shareable mappings may not be moved either,
+even if they are not currently shared.
+
+The mremap() function must be given an exact match for base address and size of
+a previously mapped object.  It may not be used to create holes in existing
+mappings, move parts of existing mappings or resize parts of mappings.  It must
+act on a complete mapping.
+
+[*] Not currently supported.
+
+
 ============================================
 PROVIDING SHAREABLE CHARACTER DEVICE SUPPORT
 ============================================
diff --git a/mm/nommu.c b/mm/nommu.c
index 4f87b2f43a2b..23cfa8ec914a 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -350,6 +350,26 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 EXPORT_SYMBOL(find_vma);
 
 /*
+ * look up the first VMA exactly that exactly matches addr
+ * - should be called with mm->mmap_sem at least held readlocked
+ */
+static inline struct vm_area_struct *find_vma_exact(struct mm_struct *mm,
+                                                    unsigned long addr)
+{
+        struct vm_list_struct *vml;
+
+        /* search the vm_start ordered list */
+        for (vml = mm->context.vmlist; vml; vml = vml->next) {
+                if (vml->vma->vm_start == addr)
+                        return vml->vma;
+                if (vml->vma->vm_start > addr)
+                        break;
+        }
+
+        return NULL;
+}
+
+/*
  * find a VMA in the global tree
  */
 static inline struct vm_area_struct *find_nommu_vma(unsigned long start)
@@ -1071,20 +1091,20 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
 }
 
 /*
- * Expand (or shrink) an existing mapping, potentially moving it at the
- * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
+ * expand (or shrink) an existing mapping, potentially moving it at the same
+ * time (controlled by the MREMAP_MAYMOVE flag and available VM space)
  *
- * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
- * This option implies MREMAP_MAYMOVE.
+ * under NOMMU conditions, we only permit changing a mapping's size, and only
+ * as long as it stays within the hole allocated by the kmalloc() call in
+ * do_mmap_pgoff() and the block is not shareable
  *
- * on uClinux, we only permit changing a mapping's size, and only as long as it stays within the
- * hole allocated by the kmalloc() call in do_mmap_pgoff() and the block is not shareable
+ * MREMAP_FIXED is not supported under NOMMU conditions
  */
 unsigned long do_mremap(unsigned long addr,
                         unsigned long old_len, unsigned long new_len,
                         unsigned long flags, unsigned long new_addr)
 {
-        struct vm_list_struct *vml = NULL;
+        struct vm_area_struct *vma;
 
         /* insanity checks first */
         if (new_len == 0)
@@ -1093,29 +1113,38 @@ unsigned long do_mremap(unsigned long addr,
         if (flags & MREMAP_FIXED && new_addr != addr)
                 return (unsigned long) -EINVAL;
 
-        for (vml = current->mm->context.vmlist; vml; vml = vml->next)
-                if (vml->vma->vm_start == addr)
-                        goto found;
-
-        return (unsigned long) -EINVAL;
+        vma = find_vma_exact(current->mm, addr);
+        if (!vma)
+                return (unsigned long) -EINVAL;
 
- found:
-        if (vml->vma->vm_end != vml->vma->vm_start + old_len)
+        if (vma->vm_end != vma->vm_start + old_len)
                 return (unsigned long) -EFAULT;
 
-        if (vml->vma->vm_flags & VM_MAYSHARE)
+        if (vma->vm_flags & VM_MAYSHARE)
                 return (unsigned long) -EPERM;
 
         if (new_len > kobjsize((void *) addr))
                 return (unsigned long) -ENOMEM;
 
         /* all checks complete - do it */
-        vml->vma->vm_end = vml->vma->vm_start + new_len;
+        vma->vm_end = vma->vm_start + new_len;
 
         askedalloc -= old_len;
         askedalloc += new_len;
 
-        return vml->vma->vm_start;
+        return vma->vm_start;
+}
+
+asmlinkage unsigned long sys_mremap(unsigned long addr,
+        unsigned long old_len, unsigned long new_len,
+        unsigned long flags, unsigned long new_addr)
+{
+        unsigned long ret;
+
+        down_write(&current->mm->mmap_sem);
+        ret = do_mremap(addr, old_len, new_len, flags, new_addr);
+        up_write(&current->mm->mmap_sem);
+        return ret;
 }
 
 struct page *follow_page(struct vm_area_struct *vma, unsigned long address,