[PATCH] Add mm->task_size and fix powerpc vdso

This patch adds mm->task_size to keep track of the task size of a given mm
and uses that to fix the powerpc vdso so that it uses the mm task size to
decide what pages to fault in instead of the current thread flags (which
broke when ptracing).

(akpm: I expect that mm_struct.task_size will become the way in which we
finally sort out the confusion between 32-bit processes and 32-bit mm's.  It
may need tweaks, but at this stage this patch is powerpc-only.)
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/powerpc/kernel/vdso.c

@@ -182,8 +182,8 @@ static struct page * vdso_vma_nopage(struct vm_area_struct * vma,
 	unsigned long offset = address - vma->vm_start;
 	struct page *pg;
 #ifdef CONFIG_PPC64
-	void *vbase = test_thread_flag(TIF_32BIT) ?
-		vdso32_kbase : vdso64_kbase;
+	void *vbase = (vma->vm_mm->task_size > TASK_SIZE_USER32) ?
+		vdso64_kbase : vdso32_kbase;
 #else
 	void *vbase = vdso32_kbase;
 #endif

fs/exec.c

@@ -885,6 +885,12 @@ int flush_old_exec(struct linux_binprm * bprm)
 	current->flags &= ~PF_RANDOMIZE;
 	flush_thread();
 
+	/* Set the new mm task size. We have to do that late because it may
+	 * depend on TIF_32BIT which is only updated in flush_thread() on
+	 * some architectures like powerpc
+	 */
+	current->mm->task_size = TASK_SIZE;
+
 	if (bprm->e_uid != current->euid || bprm->e_gid != current->egid || 
 	    file_permission(bprm->file, MAY_READ) ||
 	    (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)) {

include/linux/sched.h

@@ -299,6 +299,7 @@ struct mm_struct {
 				unsigned long pgoff, unsigned long flags);
 	void (*unmap_area) (struct mm_struct *mm, unsigned long addr);
 	unsigned long mmap_base;		/* base of mmap area */
+	unsigned long task_size;		/* size of task vm space */
 	unsigned long cached_hole_size;         /* if non-zero, the largest hole below free_area_cache */
 	unsigned long free_area_cache;		/* first hole of size cached_hole_size or larger */
 	pgd_t * pgd;