KVM: s390: provide the prefix register via kvm_run

Add the prefix register to the synced register field in kvm_run.
While we need the prefix register most of the time read-only, this
patch also adds handling for guest dirtying of the prefix register.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/s390/include/asm/kvm.h

@@ -41,7 +41,9 @@ struct kvm_debug_exit_arch {
 struct kvm_guest_debug_arch {
 };
 
+#define KVM_SYNC_PREFIX (1UL << 0)
 /* definition of registers in kvm_run */
 struct kvm_sync_regs {
+	__u64 prefix;	/* prefix register */
 };
 #endif

arch/s390/kvm/kvm-s390.c

@@ -132,6 +132,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 #ifdef CONFIG_KVM_S390_UCONTROL
 	case KVM_CAP_S390_UCONTROL:
 #endif
+	case KVM_CAP_SYNC_REGS:
 		r = 1;
 		break;
 	default:
@@ -288,6 +289,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 	}
 
 	vcpu->arch.gmap = vcpu->kvm->arch.gmap;
+	vcpu->run->kvm_valid_regs = KVM_SYNC_PREFIX;
 	return 0;
 }
 
@@ -572,6 +574,10 @@ rerun_vcpu:
 
 	vcpu->arch.sie_block->gpsw.mask = kvm_run->psw_mask;
 	vcpu->arch.sie_block->gpsw.addr = kvm_run->psw_addr;
+	if (kvm_run->kvm_dirty_regs & KVM_SYNC_PREFIX) {
+		kvm_run->kvm_dirty_regs &= ~KVM_SYNC_PREFIX;
+		kvm_s390_set_prefix(vcpu, kvm_run->s.regs.prefix);
+	}
 
 	might_fault();
 
@@ -620,6 +626,7 @@ rerun_vcpu:
 
 	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;
 
 	if (vcpu->sigset_active)
 		sigprocmask(SIG_SETMASK, &sigsaved, NULL);