KVM: s390: pci: register pci hooks without interpretation

The kvm registration hooks must be registered even if the facilities
necessary for zPCI interpretation are unavailable, as vfio-pci-zdev will
expect to use the hooks regardless.
This fixes an issue where vfio-pci-zdev will fail its open function
because of a missing kvm_register when running on hardware that does not
support zPCI interpretation.

Fixes: ca922fecda ("KVM: s390: pci: Hook to access KVM lowlevel from VFIO")
Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Link: https://lore.kernel.org/r/20220920193025.135655-1-mjrosato@linux.ibm.com
Message-Id: <20220920193025.135655-1-mjrosato@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

arch/s390/kvm/kvm-s390.c

@@ -505,7 +505,7 @@ int kvm_arch_init(void *opaque)
 		goto out;
 	}
 
-	if (kvm_s390_pci_interp_allowed()) {
+	if (IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)) {
 		rc = kvm_s390_pci_init();
 		if (rc) {
 			pr_err("Unable to allocate AIFT for PCI\n");
@@ -527,7 +527,7 @@ out:
 void kvm_arch_exit(void)
 {
 	kvm_s390_gib_destroy();
-	if (kvm_s390_pci_interp_allowed())
+	if (IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM))
 		kvm_s390_pci_exit();
 	debug_unregister(kvm_s390_dbf);
 	debug_unregister(kvm_s390_dbf_uv);

arch/s390/kvm/pci.c

@@ -672,23 +672,31 @@ out:
 
 int kvm_s390_pci_init(void)
 {
+	zpci_kvm_hook.kvm_register = kvm_s390_pci_register_kvm;
+	zpci_kvm_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
+
+	if (!kvm_s390_pci_interp_allowed())
+		return 0;
+
 	aift = kzalloc(sizeof(struct zpci_aift), GFP_KERNEL);
 	if (!aift)
 		return -ENOMEM;
 
 	spin_lock_init(&aift->gait_lock);
 	mutex_init(&aift->aift_lock);
-	zpci_kvm_hook.kvm_register = kvm_s390_pci_register_kvm;
-	zpci_kvm_hook.kvm_unregister = kvm_s390_pci_unregister_kvm;
 
 	return 0;
 }
 
 void kvm_s390_pci_exit(void)
 {
-	mutex_destroy(&aift->aift_lock);
 	zpci_kvm_hook.kvm_register = NULL;
 	zpci_kvm_hook.kvm_unregister = NULL;
 
+	if (!kvm_s390_pci_interp_allowed())
+		return;
+
+	mutex_destroy(&aift->aift_lock);
+
 	kfree(aift);
 }