mm: arch: make get_gate_vma take an mm_struct instead of a task_struct

Morally, the presence of a gate vma is more an attribute of a particular mm than
a particular task.  Moreover, dropping the dependency on task_struct will help
make both existing and future operations on mm's more flexible and convenient.

Signed-off-by: Stephen Wilson <wilsons@start.ca>
Reviewed-by: Michel Lespinasse <walken@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/x86/mm/init_64.c

@@ -861,10 +861,10 @@ static struct vm_area_struct gate_vma = {
 	.vm_flags	= VM_READ | VM_EXEC
 };
 
-struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
+struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
 {
 #ifdef CONFIG_IA32_EMULATION
-	if (test_tsk_thread_flag(tsk, TIF_IA32))
+	if (!mm || mm->context.ia32_compat)
 		return NULL;
 #endif
 	return &gate_vma;
@@ -872,7 +872,7 @@ struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
 
 int in_gate_area(struct task_struct *task, unsigned long addr)
 {
-	struct vm_area_struct *vma = get_gate_vma(task);
+	struct vm_area_struct *vma = get_gate_vma(task->mm);
 
 	if (!vma)
 		return 0;