KVM: s390: Add storage key facility interpretation control

Up to now we always expected to have the storage key facility
available for our (non-VSIE) KVM guests. For huge page support, we
need to be able to disable it, so let's introduce that now.

We add the use_skf variable to manage KVM storage key facility
usage. Also we rename use_skey in the mm context struct to uses_skeys
to make it more clear that it is an indication that the vm actively
uses storage keys.

Signed-off-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Reviewed-by: Farhan Ali <alifm@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/mm/gmap.c

@@ -2184,14 +2184,14 @@ int s390_enable_skey(void)
 	int rc = 0;
 
 	down_write(&mm->mmap_sem);
-	if (mm_use_skey(mm))
+	if (mm_uses_skeys(mm))
 		goto out_up;
 
-	mm->context.use_skey = 1;
+	mm->context.uses_skeys = 1;
 	for (vma = mm->mmap; vma; vma = vma->vm_next) {
 		if (ksm_madvise(vma, vma->vm_start, vma->vm_end,
 				MADV_UNMERGEABLE, &vma->vm_flags)) {
-			mm->context.use_skey = 0;
+			mm->context.uses_skeys = 0;
 			rc = -ENOMEM;
 			goto out_up;
 		}