diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index dc182a5b02b7055e707ef12e3fccf8859bf88a01..a27f5007062ada98c6b616f9dcee6376868c6dda 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -82,7 +82,9 @@ struct sca_block {
 
 struct kvm_s390_sie_block {
 	atomic_t cpuflags;		/* 0x0000 */
-	__u32	prefix;			/* 0x0004 */
+	__u32 : 1;			/* 0x0004 */
+	__u32 prefix : 18;
+	__u32 : 13;
 	__u8	reserved08[4];		/* 0x0008 */
 #define PROG_IN_SIE (1<<0)
 	__u32	prog0c;			/* 0x000c */
diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
index 004d385d9519e3dec901460c6775d311006b999f..0161675878a2483c7a3114ef6a82afa624a4ebcc 100644
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -23,7 +23,7 @@
 static int diag_release_pages(struct kvm_vcpu *vcpu)
 {
 	unsigned long start, end;
-	unsigned long prefix  = vcpu->arch.sie_block->prefix;
+	unsigned long prefix  = kvm_s390_get_prefix(vcpu);
 
 	start = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4];
 	end = vcpu->run->s.regs.gprs[vcpu->arch.sie_block->ipa & 0xf] + 4096;
diff --git a/arch/s390/kvm/gaccess.h b/arch/s390/kvm/gaccess.h
index 68db43e4254f5025ddff40ba1e69a6ed04d3e8b9..a07ee08ac478cbe77aab0c8118b808a0cc2b6c15 100644
--- a/arch/s390/kvm/gaccess.h
+++ b/arch/s390/kvm/gaccess.h
@@ -30,7 +30,7 @@
 static inline unsigned long kvm_s390_real_to_abs(struct kvm_vcpu *vcpu,
 						 unsigned long gra)
 {
-	unsigned long prefix = vcpu->arch.sie_block->prefix;
+	unsigned long prefix  = kvm_s390_get_prefix(vcpu);
 
 	if (gra < 2 * PAGE_SIZE)
 		gra += prefix;
@@ -99,7 +99,7 @@ static inline unsigned long kvm_s390_logical_to_effective(struct kvm_vcpu *vcpu,
 	unsigned long __gpa;					\
 								\
 	__gpa = (unsigned long)(gra);				\
-	__gpa += __vcpu->arch.sie_block->prefix;		\
+	__gpa += kvm_s390_get_prefix(__vcpu);			\
 	kvm_write_guest(__vcpu->kvm, __gpa, &__x, sizeof(__x));	\
 })
 
@@ -124,7 +124,7 @@ static inline __must_check
 int write_guest_lc(struct kvm_vcpu *vcpu, unsigned long gra, void *data,
 		   unsigned long len)
 {
-	unsigned long gpa = gra + vcpu->arch.sie_block->prefix;
+	unsigned long gpa = gra + kvm_s390_get_prefix(vcpu);
 
 	return kvm_write_guest(vcpu->kvm, gpa, data, len);
 }
@@ -150,7 +150,7 @@ static inline __must_check
 int read_guest_lc(struct kvm_vcpu *vcpu, unsigned long gra, void *data,
 		  unsigned long len)
 {
-	unsigned long gpa = gra + vcpu->arch.sie_block->prefix;
+	unsigned long gpa = gra + kvm_s390_get_prefix(vcpu);
 
 	return kvm_read_guest(vcpu->kvm, gpa, data, len);
 }
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 2c243124a4e29be59ddaa2f28b57089bbb095bc5..e519860c6031a0b5c8b24b448fd70feba1fc1fac 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -753,7 +753,7 @@ static void kvm_gmap_notifier(struct gmap *gmap, unsigned long address)
 
 	kvm_for_each_vcpu(i, vcpu, kvm) {
 		/* match against both prefix pages */
-		if (vcpu->arch.sie_block->prefix == (address & ~0x1000UL)) {
+		if (kvm_s390_get_prefix(vcpu) == (address & ~0x1000UL)) {
 			VCPU_EVENT(vcpu, 2, "gmap notifier for %lx", address);
 			kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu);
 			exit_sie_sync(vcpu);
@@ -1017,7 +1017,7 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
 	if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu)) {
 		int rc;
 		rc = gmap_ipte_notify(vcpu->arch.gmap,
-				      vcpu->arch.sie_block->prefix,
+				      kvm_s390_get_prefix(vcpu),
 				      PAGE_SIZE * 2);
 		if (rc)
 			return rc;
@@ -1338,7 +1338,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 
 	kvm_run->psw_mask     = vcpu->arch.sie_block->gpsw.mask;
 	kvm_run->psw_addr     = vcpu->arch.sie_block->gpsw.addr;
-	kvm_run->s.regs.prefix = vcpu->arch.sie_block->prefix;
+	kvm_run->s.regs.prefix = kvm_s390_get_prefix(vcpu);
 	memcpy(&kvm_run->s.regs.crs, &vcpu->arch.sie_block->gcr, 128);
 
 	if (vcpu->sigset_active)
@@ -1357,6 +1357,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 int kvm_s390_store_status_unloaded(struct kvm_vcpu *vcpu, unsigned long gpa)
 {
 	unsigned char archmode = 1;
+	unsigned int px;
 	u64 clkcomp;
 	int rc;
 
@@ -1375,8 +1376,9 @@ int kvm_s390_store_status_unloaded(struct kvm_vcpu *vcpu, unsigned long gpa)
 			      vcpu->run->s.regs.gprs, 128);
 	rc |= write_guest_abs(vcpu, gpa + offsetof(struct save_area, psw),
 			      &vcpu->arch.sie_block->gpsw, 16);
+	px = kvm_s390_get_prefix(vcpu);
 	rc |= write_guest_abs(vcpu, gpa + offsetof(struct save_area, pref_reg),
-			      &vcpu->arch.sie_block->prefix, 4);
+			      &px, 4);
 	rc |= write_guest_abs(vcpu,
 			      gpa + offsetof(struct save_area, fp_ctrl_reg),
 			      &vcpu->arch.guest_fpregs.fpc, 4);
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index 87edfc919db98c21b2bb5cdd8282a8e6db201491..a8655ed31616746adc2fb2e7e454b22451e2f60e 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -61,9 +61,15 @@ static inline int kvm_is_ucontrol(struct kvm *kvm)
 #endif
 }
 
+#define GUEST_PREFIX_SHIFT 13
+static inline u32 kvm_s390_get_prefix(struct kvm_vcpu *vcpu)
+{
+	return vcpu->arch.sie_block->prefix << GUEST_PREFIX_SHIFT;
+}
+
 static inline void kvm_s390_set_prefix(struct kvm_vcpu *vcpu, u32 prefix)
 {
-	vcpu->arch.sie_block->prefix = prefix & 0x7fffe000u;
+	vcpu->arch.sie_block->prefix = prefix >> GUEST_PREFIX_SHIFT;
 	vcpu->arch.sie_block->ihcpu  = 0xffff;
 	kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu);
 }
diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index d99f5f0305a084187e8559665be80050a3fade26..6296159ac883e07e90951805fa4e1b4bed94d480 100644
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -119,8 +119,7 @@ static int handle_store_prefix(struct kvm_vcpu *vcpu)
 	if (operand2 & 3)
 		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
 
-	address = vcpu->arch.sie_block->prefix;
-	address = address & 0x7fffe000u;
+	address = kvm_s390_get_prefix(vcpu);
 
 	/* get the value */
 	rc = write_guest(vcpu, operand2, &address, sizeof(address));