KVM: s390: resetting the Topology-Change-Report

During a subsystem reset the Topology-Change-Report is cleared.

Let's give userland the possibility to clear the MTCR in the case
of a subsystem reset.

To migrate the MTCR, we give userland the possibility to
query the MTCR state.

We indicate KVM support for the CPU topology facility with a new
KVM capability: KVM_CAP_S390_CPU_TOPOLOGY.
Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Reviewed-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Message-Id: <20220714194334.127812-1-pmorel@linux.ibm.com>
Link: https://lore.kernel.org/all/20220714194334.127812-1-pmorel@linux.ibm.com/
[frankja@linux.ibm.com: Simple conflict resolution in Documentation/virt/kvm/api.rst]
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

Documentation/virt/kvm/api.rst

@@ -8269,6 +8269,31 @@ The capability has no effect if the nx_huge_pages module parameter is not set.
 
 This capability may only be set before any vCPUs are created.
 
+8.39 KVM_CAP_S390_CPU_TOPOLOGY
+------------------------------
+
+:Capability: KVM_CAP_S390_CPU_TOPOLOGY
+:Architectures: s390
+:Type: vm
+
+This capability indicates that KVM will provide the S390 CPU Topology
+facility which consist of the interpretation of the PTF instruction for
+the function code 2 along with interception and forwarding of both the
+PTF instruction with function codes 0 or 1 and the STSI(15,1,x)
+instruction to the userland hypervisor.
+
+The stfle facility 11, CPU Topology facility, should not be indicated
+to the guest without this capability.
+
+When this capability is present, KVM provides a new attribute group
+on vm fd, KVM_S390_VM_CPU_TOPOLOGY.
+This new attribute allows to get, set or clear the Modified Change
+Topology Report (MTCR) bit of the SCA through the kvm_device_attr
+structure.
+
+When getting the Modified Change Topology Report value, the attr->addr
+must point to a byte where the value will be stored or retrieved from.
+
 9. Known KVM API problems
 =========================
 

arch/s390/include/uapi/asm/kvm.h

@@ -74,6 +74,7 @@ struct kvm_s390_io_adapter_req {
 #define KVM_S390_VM_CRYPTO		2
 #define KVM_S390_VM_CPU_MODEL		3
 #define KVM_S390_VM_MIGRATION		4
+#define KVM_S390_VM_CPU_TOPOLOGY	5
 
 /* kvm attributes for mem_ctrl */
 #define KVM_S390_VM_MEM_ENABLE_CMMA	0

arch/s390/kvm/kvm-s390.c

@@ -642,6 +642,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_S390_ZPCI_OP:
 		r = kvm_s390_pci_interp_allowed();
 		break;
+	case KVM_CAP_S390_CPU_TOPOLOGY:
+		r = test_facility(11);
+		break;
 	default:
 		r = 0;
 	}
@@ -853,6 +856,20 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
 		icpt_operexc_on_all_vcpus(kvm);
 		r = 0;
 		break;
+	case KVM_CAP_S390_CPU_TOPOLOGY:
+		r = -EINVAL;
+		mutex_lock(&kvm->lock);
+		if (kvm->created_vcpus) {
+			r = -EBUSY;
+		} else if (test_facility(11)) {
+			set_kvm_facility(kvm->arch.model.fac_mask, 11);
+			set_kvm_facility(kvm->arch.model.fac_list, 11);
+			r = 0;
+		}
+		mutex_unlock(&kvm->lock);
+		VM_EVENT(kvm, 3, "ENABLE: CAP_S390_CPU_TOPOLOGY %s",
+			 r ? "(not available)" : "(success)");
+		break;
 	default:
 		r = -EINVAL;
 		break;
@@ -1789,6 +1806,31 @@ static void kvm_s390_update_topology_change_report(struct kvm *kvm, bool val)
 	read_unlock(&kvm->arch.sca_lock);
 }
 
+static int kvm_s390_set_topo_change_indication(struct kvm *kvm,
+					       struct kvm_device_attr *attr)
+{
+	if (!test_kvm_facility(kvm, 11))
+		return -ENXIO;
+
+	kvm_s390_update_topology_change_report(kvm, !!attr->attr);
+	return 0;
+}
+
+static int kvm_s390_get_topo_change_indication(struct kvm *kvm,
+					       struct kvm_device_attr *attr)
+{
+	u8 topo;
+
+	if (!test_kvm_facility(kvm, 11))
+		return -ENXIO;
+
+	read_lock(&kvm->arch.sca_lock);
+	topo = ((struct bsca_block *)kvm->arch.sca)->utility.mtcr;
+	read_unlock(&kvm->arch.sca_lock);
+
+	return put_user(topo, (u8 __user *)attr->addr);
+}
+
 static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 {
 	int ret;
@@ -1809,6 +1851,9 @@ static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 	case KVM_S390_VM_MIGRATION:
 		ret = kvm_s390_vm_set_migration(kvm, attr);
 		break;
+	case KVM_S390_VM_CPU_TOPOLOGY:
+		ret = kvm_s390_set_topo_change_indication(kvm, attr);
+		break;
 	default:
 		ret = -ENXIO;
 		break;
@@ -1834,6 +1879,9 @@ static int kvm_s390_vm_get_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 	case KVM_S390_VM_MIGRATION:
 		ret = kvm_s390_vm_get_migration(kvm, attr);
 		break;
+	case KVM_S390_VM_CPU_TOPOLOGY:
+		ret = kvm_s390_get_topo_change_indication(kvm, attr);
+		break;
 	default:
 		ret = -ENXIO;
 		break;
@@ -1907,6 +1955,9 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 	case KVM_S390_VM_MIGRATION:
 		ret = 0;
 		break;
+	case KVM_S390_VM_CPU_TOPOLOGY:
+		ret = test_kvm_facility(kvm, 11) ? 0 : -ENXIO;
+		break;
 	default:
 		ret = -ENXIO;
 		break;

include/uapi/linux/kvm.h

@@ -1168,6 +1168,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_X86_NOTIFY_VMEXIT 219
 #define KVM_CAP_VM_DISABLE_NX_HUGE_PAGES 220
 #define KVM_CAP_S390_ZPCI_OP 221
+#define KVM_CAP_S390_CPU_TOPOLOGY 222
 
 #ifdef KVM_CAP_IRQ_ROUTING