kvm-vfio: do not use module_init

/me got confused between the kernel and QEMU.  In the kernel, you can
only have one module_init function, and it will prevent unloading the
module unless you also have the corresponding module_exit function.

So, commit 80ce1639727e (KVM: VFIO: register kvm_device_ops dynamically,
2014-09-02) broke unloading of the kvm module, by adding a module_init
function and no module_exit.

Repair it by making kvm_vfio_ops_init weak, and checking it in
kvm_init.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Alex Williamson <Alex.Williamson@redhat.com>
Fixes: 80ce1639727e9d38729c34f162378508c307ca25
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 19 insertions, 2 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index db57363cc287..499db0977f3c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -57,6 +57,7 @@
 
 #include "coalesced_mmio.h"
 #include "async_pf.h"
+#include "vfio.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/kvm.h>
@@ -3226,6 +3227,9 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
                 goto out_undebugfs;
         }
 
+        r = kvm_vfio_ops_init();
+        WARN_ON(r);
+
         return 0;
 
 out_undebugfs:
diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
index bb11b36ee8a2..281e7cf2b8e5 100644
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <linux/vfio.h>
+#include "vfio.h"
 
 struct kvm_vfio_group {
         struct list_head node;
@@ -278,8 +279,7 @@ static int kvm_vfio_create(struct kvm_device *dev, u32 type)
         return 0;
 }
 
-static int __init kvm_vfio_ops_init(void)
+int kvm_vfio_ops_init(void)
 {
         return kvm_register_device_ops(&kvm_vfio_ops, KVM_DEV_TYPE_VFIO);
 }
-module_init(kvm_vfio_ops_init);
diff --git a/virt/kvm/vfio.h b/virt/kvm/vfio.h
new file mode 100644
index 000000000000..92eac75d6b62
--- /dev/null
+++ b/virt/kvm/vfio.h
@@ -0,0 +1,13 @@
+#ifndef __KVM_VFIO_H
+#define __KVM_VFIO_H
+
+#ifdef CONFIG_KVM_VFIO
+int kvm_vfio_ops_init(void);
+#else
+static inline int kvm_vfio_ops_init(void)
+{
+        return 0;
+}
+#endif
+
+#endif