KVM: s390: provide a capability for AIS state migration

The AIS capability was introduced in 4.12, while the interface to
migrate the state was added in 4.13. Unfortunately it is not possible
for userspace to detect the migration capability without creating a flic
kvm device. As in QEMU the cpu model detection runs on the "none"
machine this will result in cpu model issues regarding the "ais"
capability.

To get the "ais" capability properly let's add a new KVM capability that
tells userspace that AIS states can be migrated.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Halil Pasic <pasic@linux.vnet.ibm.com>

Documentation/virtual/kvm/api.txt

@@ -4347,3 +4347,12 @@ This capability indicates that userspace can load HV_X64_MSR_VP_INDEX msr.  Its
 value is used to denote the target vcpu for a SynIC interrupt.  For
 compatibilty, KVM initializes this msr to KVM's internal vcpu index.  When this
 capability is absent, userspace can still query this msr's value.
+
+8.13 KVM_CAP_S390_AIS_MIGRATION
+
+Architectures: s390
+Parameters: none
+
+This capability indicates if the flic device will be able to get/set the
+AIS states for migration via the KVM_DEV_FLIC_AISM_ALL attribute and allows
+to discover this without having to create a flic device.

Documentation/virtual/kvm/devices/s390_flic.txt

@@ -151,6 +151,8 @@ struct kvm_s390_ais_all {
     to an ISC (MSB0 bit 0 to ISC 0 and so on). The combination of simm bit and
     nimm bit presents AIS mode for a ISC.
 
+    KVM_DEV_FLIC_AISM_ALL is indicated by KVM_CAP_S390_AIS_MIGRATION.
+
 Note: The KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR device ioctls executed on
 FLIC with an unknown group or attribute gives the error code EINVAL (instead of
 ENXIO, as specified in the API documentation). It is not possible to conclude

arch/s390/kvm/kvm-s390.c

@@ -395,6 +395,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_S390_USER_INSTR0:
 	case KVM_CAP_S390_CMMA_MIGRATION:
 	case KVM_CAP_S390_AIS:
+	case KVM_CAP_S390_AIS_MIGRATION:
 		r = 1;
 		break;
 	case KVM_CAP_S390_MEM_OP:

include/uapi/linux/kvm.h

@@ -930,6 +930,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_PPC_SMT_POSSIBLE 147
 #define KVM_CAP_HYPERV_SYNIC2 148
 #define KVM_CAP_HYPERV_VP_INDEX 149
+#define KVM_CAP_S390_AIS_MIGRATION 150
 
 #ifdef KVM_CAP_IRQ_ROUTING