mm: special mapping nopage

Convert special mapping install from nopage to fault.

Because the "vm_file" is NULL for the special mapping, the generic VM
code has messed up "vm_pgoff" thinking that it's an anonymous mapping
and the offset does't matter.  For that reason, we need to undo the
vm_pgoff offset that got added into vmf->pgoff.

[ We _really_ should clean that up - either by making this whole special
  mapping code just use a real file entry rather than that ugly array of
  "struct page" pointers, or by just making the VM code realize that
  even if vm_file is NULL it may not be a regular anonymous mmap.
							 - Linus ]

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index ad6e4ea..a32d28c 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2165,24 +2165,31 @@ int may_expand_vm(struct mm_struct *mm, unsigned long npages)
 }
 
 
-static struct page *special_mapping_nopage(struct vm_area_struct *vma,
-                                          unsigned long address, int *type)
+static int special_mapping_fault(struct vm_area_struct *vma,
+                               struct vm_fault *vmf)
 {
+       pgoff_t pgoff;
        struct page **pages;
 
-       BUG_ON(address < vma->vm_start || address >= vma->vm_end);
+       /*
+        * special mappings have no vm_file, and in that case, the mm
+        * uses vm_pgoff internally. So we have to subtract it from here.
+        * We are allowed to do this because we are the mm; do not copy
+        * this code into drivers!
+        */
+       pgoff = vmf->pgoff - vma->vm_pgoff;
 
-       address -= vma->vm_start;
-       for (pages = vma->vm_private_data; address > 0 && *pages; ++pages)
-               address -= PAGE_SIZE;
+       for (pages = vma->vm_private_data; pgoff && *pages; ++pages)
+               pgoff--;
 
        if (*pages) {
                struct page *page = *pages;
                get_page(page);
-               return page;
+               vmf->page = page;
+               return 0;
        }
 
-       return NOPAGE_SIGBUS;
+       return VM_FAULT_SIGBUS;
 }
 
 /*
@@ -2194,7 +2201,7 @@ static void special_mapping_close(struct vm_area_struct *vma)
 
 static struct vm_operations_struct special_mapping_vmops = {
        .close = special_mapping_close,
-       .nopage = special_mapping_nopage,
+       .fault = special_mapping_fault,
 };
 
 /*