s390/kvm: bad rss-counter state

commit c3f0327f
    mm: add rss counters consistency check
detected the following problem with kvm on s390:

BUG: Bad rss-counter state mm:00000004f73ef000 idx:0 val:-10
BUG: Bad rss-counter state mm:00000004f73ef000 idx:1 val:-5

We have to make sure that we accumulate all rss values into
the mm before we replace the mm to avoid triggering this (harmless)
bug message.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/pgtable.c

@@ -822,6 +822,8 @@ int s390_enable_sie(void)
 
 	/* we copy the mm and let dup_mm create the page tables with_pgstes */
 	tsk->mm->context.alloc_pgste = 1;
+	/* make sure that both mms have a correct rss state */
+	sync_mm_rss(tsk->mm);
 	mm = dup_mm(tsk);
 	tsk->mm->context.alloc_pgste = 0;
 	if (!mm)