[PATCH] freepgt: free_pgtables from FIRST_USER_ADDRESS

The patches to free_pgtables by vma left problems on any architectures which
leave some user address page table entries unencapsulated by vma.  Andi has
fixed the 32-bit vDSO on x86_64 to use a vma.  Now fix arm (and arm26), whose
first PAGE_SIZE is reserved (perhaps) for machine vectors.

Our calls to free_pgtables must not touch that area, and exit_mmap's
BUG_ON(nr_ptes) must allow that arm's get_pgd_slow may (or may not) have
allocated an extra page table, which its free_pgd_slow would free later.

FIRST_USER_PGD_NR has misled me and others: until all the arches define
FIRST_USER_ADDRESS instead, a hack in mmap.c to derive one from t'other.  This
patch fixes the bugs, the remaining patches just clean it up.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 0fa87a5ae2cc..ac6e694c3b61 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1612,6 +1612,11 @@ static void unmap_vma_list(struct mm_struct *mm, struct vm_area_struct *vma)
         validate_mm(mm);
 }
 
+#ifndef FIRST_USER_ADDRESS      /* temporary hack */
+#define THIS_IS_ARM             FIRST_USER_PGD_NR
+#define FIRST_USER_ADDRESS      (THIS_IS_ARM * PAGE_SIZE)
+#endif
+
 /*
  * Get rid of page table information in the indicated region.
  *
@@ -1630,7 +1635,7 @@ static void unmap_region(struct mm_struct *mm,
         tlb = tlb_gather_mmu(mm, 0);
         unmap_vmas(&tlb, mm, vma, start, end, &nr_accounted, NULL);
         vm_unacct_memory(nr_accounted);
-        free_pgtables(&tlb, vma, prev? prev->vm_end: 0,
+        free_pgtables(&tlb, vma, prev? prev->vm_end: FIRST_USER_ADDRESS,
                                  next? next->vm_start: 0);
         tlb_finish_mmu(tlb, start, end);
         spin_unlock(&mm->page_table_lock);
@@ -1910,7 +1915,7 @@ void exit_mmap(struct mm_struct *mm)
         /* Use -1 here to ensure all VMAs in the mm are unmapped */
         end = unmap_vmas(&tlb, mm, vma, 0, -1, &nr_accounted, NULL);
         vm_unacct_memory(nr_accounted);
-        free_pgtables(&tlb, vma, 0, 0);
+        free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
         tlb_finish_mmu(tlb, 0, end);
 
         mm->mmap = mm->mmap_cache = NULL;
@@ -1931,7 +1936,7 @@ void exit_mmap(struct mm_struct *mm)
                 vma = next;
         }
 
-        BUG_ON(mm->nr_ptes);    /* This is just debugging */
+        BUG_ON(mm->nr_ptes > (FIRST_USER_ADDRESS+PMD_SIZE-1)>>PMD_SHIFT);
 }
 
 /* Insert vm structure into process list sorted by address