[PATCH 1/2] KVM: device: add simple registration mechanism for kvm_device_ops

[Will Deacon <will.deacon@arm.com>]

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.

I didn't try to port all current drivers over, as it's not always clear
which initialisation hook the ops should be registered from.

Cc: Gleb Natapov <gleb@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---

Hi guys,

I've just started writing a virtual IOMMU for the ARM SMMU and figured a
registration mechanism for kvm_device_ops would be a nice cleanup for
that.

Will

 include/linux/kvm_host.h |  1 +
 include/uapi/linux/kvm.h |  1 +
 virt/kvm/kvm_main.c      | 65 ++++++++++++++++++++++++++++--------------------
 3 files changed, 40 insertions(+), 27 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ec4e3bd83d47..b75faaf0d76d 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1083,6 +1083,7 @@ 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 e11d8f170a62..3b368166286f 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -949,6 +949,7 @@ struct kvm_device_attr {
 #define   KVM_DEV_VFIO_GROUP_DEL			2
 #define KVM_DEV_TYPE_ARM_VGIC_V2	5
 #define KVM_DEV_TYPE_FLIC		6
+#define KVM_DEV_TYPE_MAX		7
 
 /*
  * ioctls for VM fds
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4b6c01b477f9..a0c6cc31a1f6 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2257,44 +2257,55 @@ 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 >= KVM_DEV_TYPE_MAX)
+		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 >= KVM_DEV_TYPE_MAX)
+		return -ENODEV;
+
+	ops = kvm_device_ops_table[cd->type];
+	if (ops == NULL)
 		return -ENODEV;
-	}
 
 	if (test)
 		return 0;
-- 
2.0.0