KVM: s390: split kvm_s390_real_to_abs

A new function _kvm_s390_real_to_abs will apply prefixing to a real address
with a given prefix value.

The old kvm_s390_real_to_abs becomes now a wrapper around the new function.

This is needed to avoid code duplication in vSIE.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210322140559.500716-2-imbrenda@linux.ibm.com
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/kvm/gaccess.h

@@ -16,6 +16,23 @@
 #include <linux/ptrace.h>
 #include "kvm-s390.h"
 
+/**
+ * kvm_s390_real_to_abs - convert guest real address to guest absolute address
+ * @prefix - guest prefix
+ * @gra - guest real address
+ *
+ * Returns the guest absolute address that corresponds to the passed guest real
+ * address @gra of by applying the given prefix.
+ */
+static inline unsigned long _kvm_s390_real_to_abs(u32 prefix, unsigned long gra)
+{
+	if (gra < 2 * PAGE_SIZE)
+		gra += prefix;
+	else if (gra >= prefix && gra < prefix + 2 * PAGE_SIZE)
+		gra -= prefix;
+	return gra;
+}
+
 /**
  * kvm_s390_real_to_abs - convert guest real address to guest absolute address
  * @vcpu - guest virtual cpu
@@ -27,13 +44,7 @@
 static inline unsigned long kvm_s390_real_to_abs(struct kvm_vcpu *vcpu,
 						 unsigned long gra)
 {
-	unsigned long prefix  = kvm_s390_get_prefix(vcpu);
+	return _kvm_s390_real_to_abs(kvm_s390_get_prefix(vcpu), gra);
-
-	if (gra < 2 * PAGE_SIZE)
-		gra += prefix;
-	else if (gra >= prefix && gra < prefix + 2 * PAGE_SIZE)
-		gra -= prefix;
-	return gra;
 }
 
 /**