[S390] kvm: Fix badness at include/asm/mmu_context.h:83

commit 050eef364ad700590a605a0749f825cab4834b1e
    [S390] fix tlb flushing vs. concurrent /proc accesses
broke KVM on s390x. On every schedule a
Badness at include/asm/mmu_context.h:83 appears. s390_enable_sie
replaces the mm on the __running__ task, therefore, we have to
increase the attach count of the new mm.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/pgtable.c

@@ -449,6 +449,8 @@ int s390_enable_sie(void)
 	tsk->mm = tsk->active_mm = mm;
 	preempt_disable();
 	update_mm(mm, tsk);
+	atomic_inc(&mm->context.attach_count);
+	atomic_dec(&old_mm->context.attach_count);
 	cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
 	preempt_enable();
 	task_unlock(tsk);