mm: allow arch code to control the user page table ceiling

On architectures where a pgd entry may be shared between user and kernel
(e.g.  ARM+LPAE), freeing page tables needs a ceiling other than 0.
This patch introduces a generic USER_PGTABLES_CEILING that arch code can
override.  It is the responsibility of the arch code setting the ceiling
to ensure the complete freeing of the page tables (usually in
pgd_free()).

[catalin.marinas@arm.com: commit log; shift_arg_pages(), asm-generic/pgtables.h changes]
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: <stable@vger.kernel.org>	[3.3+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/exec.c b/fs/exec.c
index a96a4885bbbf..87e731f020fb 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -613,7 +613,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
                  * when the old and new regions overlap clear from new_end.
                  */
                 free_pgd_range(&tlb, new_end, old_end, new_end,
-                        vma->vm_next ? vma->vm_next->vm_start : 0);
+                        vma->vm_next ? vma->vm_next->vm_start : USER_PGTABLES_CEILING);
         } else {
                 /*
                  * otherwise, clean from old_start; this is done to not touch
@@ -622,7 +622,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
                  * for the others its just a little faster.
                  */
                 free_pgd_range(&tlb, old_start, old_end, new_end,
-                        vma->vm_next ? vma->vm_next->vm_start : 0);
+                        vma->vm_next ? vma->vm_next->vm_start : USER_PGTABLES_CEILING);
         }
         tlb_finish_mmu(&tlb, new_end, old_end);