[PATCH 1/6] freepgt2: free_pgtables from FIRST_USER_ADDRESS

[Hugh Dickins <hugh@veritas.com>]

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>
---

 mm/mmap.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

--- 2.6.12-rc2-mm1/mm/mmap.c	2005-04-05 15:23:00.000000000 +0100
+++ linux/mm/mmap.c	2005-04-05 18:59:01.000000000 +0100
@@ -1608,6 +1608,11 @@ static void unmap_vma_list(struct mm_str
 	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.
  *
@@ -1626,7 +1631,7 @@ static void unmap_region(struct mm_struc
 	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);
@@ -1906,7 +1911,7 @@ 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;
@@ -1927,7 +1932,7 @@ 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