KVM: device: add simple registration mechanism for kvm_device_ops

kvm_ioctl_create_device currently has knowledge of all the device types
and their associated ops. This is fairly inflexible when adding support
for new in-kernel device emulations, so move what we currently have out
into a table, which can support dynamic registration of ops by new
drivers for virtual hardware.

Cc: Alex Williamson <Alex.Williamson@redhat.com>
Cc: Alex Graf <agraf@suse.de>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 55 insertions, 33 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e098dce179df..b6e954742951 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1064,6 +1064,7 @@ struct kvm_device_ops {
 void kvm_device_get(struct kvm_device *dev);
 void kvm_device_put(struct kvm_device *dev);
 struct kvm_device *kvm_device_from_filp(struct file *filp);
+int kvm_register_device_ops(struct kvm_device_ops *ops, u32 type);
 
 extern struct kvm_device_ops kvm_mpic_ops;
 extern struct kvm_device_ops kvm_xics_ops;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 0695a1e3e332..60768822b140 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -943,15 +943,25 @@ struct kvm_device_attr {
         __u64   addr;           /* userspace address of attr data */
 };
 
-#define KVM_DEV_TYPE_FSL_MPIC_20        1
-#define KVM_DEV_TYPE_FSL_MPIC_42        2
-#define KVM_DEV_TYPE_XICS               3
-#define KVM_DEV_TYPE_VFIO               4
 #define  KVM_DEV_VFIO_GROUP                     1
 #define   KVM_DEV_VFIO_GROUP_ADD                        1
 #define   KVM_DEV_VFIO_GROUP_DEL                        2
-#define KVM_DEV_TYPE_ARM_VGIC_V2        5
-#define KVM_DEV_TYPE_FLIC               6
+
+enum kvm_device_type {
+        KVM_DEV_TYPE_FSL_MPIC_20        = 1,
+#define KVM_DEV_TYPE_FSL_MPIC_20        KVM_DEV_TYPE_FSL_MPIC_20
+        KVM_DEV_TYPE_FSL_MPIC_42,
+#define KVM_DEV_TYPE_FSL_MPIC_42        KVM_DEV_TYPE_FSL_MPIC_42
+        KVM_DEV_TYPE_XICS,
+#define KVM_DEV_TYPE_XICS               KVM_DEV_TYPE_XICS
+        KVM_DEV_TYPE_VFIO,
+#define KVM_DEV_TYPE_VFIO               KVM_DEV_TYPE_VFIO
+        KVM_DEV_TYPE_ARM_VGIC_V2,
+#define KVM_DEV_TYPE_ARM_VGIC_V2        KVM_DEV_TYPE_ARM_VGIC_V2
+        KVM_DEV_TYPE_FLIC,
+#define KVM_DEV_TYPE_FLIC               KVM_DEV_TYPE_FLIC
+        KVM_DEV_TYPE_MAX,
+};
 
 /*
  * ioctls for VM fds
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c338599804e0..686d783387a0 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2272,44 +2272,55 @@ struct kvm_device *kvm_device_from_filp(struct file *filp)
         return filp->private_data;
 }
 
-static int kvm_ioctl_create_device(struct kvm *kvm,
-                                   struct kvm_create_device *cd)
-{
-        struct kvm_device_ops *ops = NULL;
-        struct kvm_device *dev;
-        bool test = cd->flags & KVM_CREATE_DEVICE_TEST;
-        int ret;
-
-        switch (cd->type) {
+static struct kvm_device_ops *kvm_device_ops_table[KVM_DEV_TYPE_MAX] = {
 #ifdef CONFIG_KVM_MPIC
-        case KVM_DEV_TYPE_FSL_MPIC_20:
-        case KVM_DEV_TYPE_FSL_MPIC_42:
-                ops = &kvm_mpic_ops;
-                break;
+        [KVM_DEV_TYPE_FSL_MPIC_20]      = &kvm_mpic_ops,
+        [KVM_DEV_TYPE_FSL_MPIC_42]      = &kvm_mpic_ops,
 #endif
+
 #ifdef CONFIG_KVM_XICS
-        case KVM_DEV_TYPE_XICS:
-                ops = &kvm_xics_ops;
-                break;
+        [KVM_DEV_TYPE_XICS]             = &kvm_xics_ops,
 #endif
+
 #ifdef CONFIG_KVM_VFIO
-        case KVM_DEV_TYPE_VFIO:
-                ops = &kvm_vfio_ops;
-                break;
+        [KVM_DEV_TYPE_VFIO]             = &kvm_vfio_ops,
 #endif
+
 #ifdef CONFIG_KVM_ARM_VGIC
-        case KVM_DEV_TYPE_ARM_VGIC_V2:
-                ops = &kvm_arm_vgic_v2_ops;
-                break;
+        [KVM_DEV_TYPE_ARM_VGIC_V2]      = &kvm_arm_vgic_v2_ops,
 #endif
+
 #ifdef CONFIG_S390
-        case KVM_DEV_TYPE_FLIC:
-                ops = &kvm_flic_ops;
-                break;
+        [KVM_DEV_TYPE_FLIC]             = &kvm_flic_ops,
 #endif
-        default:
+};
+
+int kvm_register_device_ops(struct kvm_device_ops *ops, u32 type)
+{
+        if (type >= ARRAY_SIZE(kvm_device_ops_table))
+                return -ENOSPC;
+
+        if (kvm_device_ops_table[type] != NULL)
+                return -EEXIST;
+
+        kvm_device_ops_table[type] = ops;
+        return 0;
+}
+
+static int kvm_ioctl_create_device(struct kvm *kvm,
+                                   struct kvm_create_device *cd)
+{
+        struct kvm_device_ops *ops = NULL;
+        struct kvm_device *dev;
+        bool test = cd->flags & KVM_CREATE_DEVICE_TEST;
+        int ret;
+
+        if (cd->type >= ARRAY_SIZE(kvm_device_ops_table))
+                return -ENODEV;
+
+        ops = kvm_device_ops_table[cd->type];
+        if (ops == NULL)
                 return -ENODEV;
-        }
 
         if (test)
                 return 0;