[PATCH 1/3] VFIO: take reference to the KVM module

[Paolo Bonzini <pbonzini@redhat.com>]

VFIO is implicitly taking a reference to the KVM module between
vfio_device_get_kvm_safe and vfio_device_put_kvm, thanks to
symbol_get and symbol_put.

In preparation for removing symbol_get and symbol_put themselves
from VFIO, actually store a pointer to the KVM module and use
module_get()/module_put() to keep KVM alive.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 drivers/vfio/device_cdev.c |  2 +-
 drivers/vfio/group.c       |  5 +++--
 drivers/vfio/vfio.h        | 15 ++++++++++-----
 drivers/vfio/vfio_main.c   | 39 +++++++++++++++++++++++---------------
 include/linux/vfio.h       |  3 ++-
 virt/kvm/vfio.c            |  4 ++--
 6 files changed, 42 insertions(+), 26 deletions(-)

diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
index 8ceca24ac136..a67d7215c239 100644
--- a/drivers/vfio/device_cdev.c
+++ b/drivers/vfio/device_cdev.c
@@ -56,7 +56,7 @@ int vfio_device_fops_cdev_open(struct inode *inode, struct file *filep)
 static void vfio_df_get_kvm_safe(struct vfio_device_file *df)
 {
 	spin_lock(&df->kvm_ref_lock);
-	vfio_device_get_kvm_safe(df->device, df->kvm);
+	vfio_device_get_kvm_safe(df->device, df->kvm, df->kvm_module);
 	spin_unlock(&df->kvm_ref_lock);
 }
 
diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c
index 4f15016d2a5f..7d28f45fefaa 100644
--- a/drivers/vfio/group.c
+++ b/drivers/vfio/group.c
@@ -158,7 +158,7 @@ static int vfio_group_ioctl_set_container(struct vfio_group *group,
 static void vfio_device_group_get_kvm_safe(struct vfio_device *device)
 {
 	spin_lock(&device->group->kvm_ref_lock);
-	vfio_device_get_kvm_safe(device, device->group->kvm);
+	vfio_device_get_kvm_safe(device, device->group->kvm, device->group->kvm_module);
 	spin_unlock(&device->group->kvm_ref_lock);
 }
 
@@ -858,10 +858,11 @@ bool vfio_group_enforced_coherent(struct vfio_group *group)
 	return ret;
 }
 
-void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
+void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm, struct module *kvm_module)
 {
 	spin_lock(&group->kvm_ref_lock);
 	group->kvm = kvm;
+	group->kvm_module = kvm_module;
 	spin_unlock(&group->kvm_ref_lock);
 }
 
diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
index 50128da18bca..a0c38f89b30a 100644
--- a/drivers/vfio/vfio.h
+++ b/drivers/vfio/vfio.h
@@ -22,8 +22,9 @@ struct vfio_device_file {
 
 	u8 access_granted;
 	u32 devid; /* only valid when iommufd is valid */
-	spinlock_t kvm_ref_lock; /* protect kvm field */
+	spinlock_t kvm_ref_lock; /* protect kvm and kvm_module fields */
 	struct kvm *kvm;
+	struct module *kvm_module;
 	struct iommufd_ctx *iommufd; /* protected by struct vfio_device_set::lock */
 };
 
@@ -89,6 +90,7 @@ struct vfio_group {
 	enum vfio_group_type		type;
 	struct mutex			group_lock;
 	struct kvm			*kvm;
+	struct module			*kvm_module;
 	struct file			*opened_file;
 	struct blocking_notifier_head	notifier;
 	struct iommufd_ctx		*iommufd;
@@ -108,7 +110,7 @@ void vfio_device_group_unuse_iommu(struct vfio_device *device);
 void vfio_df_group_close(struct vfio_device_file *df);
 struct vfio_group *vfio_group_from_file(struct file *file);
 bool vfio_group_enforced_coherent(struct vfio_group *group);
-void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm);
+void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm, struct module *kvm_module);
 bool vfio_device_has_container(struct vfio_device *device);
 int __init vfio_group_init(void);
 void vfio_group_cleanup(void);
@@ -171,7 +173,8 @@ static inline bool vfio_group_enforced_coherent(struct vfio_group *group)
 	return true;
 }
 
-static inline void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
+static inline void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm,
+				      struct module *kvm_module)
 {
 }
 
@@ -435,11 +438,13 @@ static inline void vfio_virqfd_exit(void)
 #endif
 
 #if IS_ENABLED(CONFIG_KVM)
-void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm);
+void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm,
+			      struct module *kvm_module);
 void vfio_device_put_kvm(struct vfio_device *device);
 #else
 static inline void vfio_device_get_kvm_safe(struct vfio_device *device,
-					    struct kvm *kvm)
+					    struct kvm *kvm,
+					    struct module *kvm_module)
 {
 }
 
diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 742477546b15..d1bbc42d484a 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -433,7 +433,7 @@ void vfio_unregister_group_dev(struct vfio_device *device)
 EXPORT_SYMBOL_GPL(vfio_unregister_group_dev);
 
 #if IS_ENABLED(CONFIG_KVM)
-void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm)
+void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm, struct module *kvm_module)
 {
 	void (*pfn)(struct kvm *kvm);
 	bool (*fn)(struct kvm *kvm);
@@ -444,25 +444,31 @@ void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm)
 	if (!kvm)
 		return;
 
-	pfn = symbol_get(kvm_put_kvm);
-	if (WARN_ON(!pfn))
+	if (!try_module_get(kvm_module))
 		return;
 
+	pfn = symbol_get(kvm_put_kvm);
+	if (WARN_ON(!pfn))
+		goto out_put_mod;
+
 	fn = symbol_get(kvm_get_kvm_safe);
-	if (WARN_ON(!fn)) {
-		symbol_put(kvm_put_kvm);
-		return;
-	}
+	if (WARN_ON(!fn))
+		goto out_put_sym;
 
 	ret = fn(kvm);
 	symbol_put(kvm_get_kvm_safe);
-	if (!ret) {
-		symbol_put(kvm_put_kvm);
-		return;
-	}
+	if (!ret)
+		goto out_put_sym;
 
 	device->put_kvm = pfn;
 	device->kvm = kvm;
+	device->kvm_module = kvm_module;
+	return;
+
+out_put_sym:
+	symbol_put(kvm_put_kvm);
+out_put_mod:
+	module_put(kvm_module);
 }
 
 void vfio_device_put_kvm(struct vfio_device *device)
@@ -481,6 +487,8 @@ void vfio_device_put_kvm(struct vfio_device *device)
 
 clear:
 	device->kvm = NULL;
+	module_put(device->kvm_module);
+	device->kvm_module = NULL;
 }
 #endif
 
@@ -1483,7 +1491,7 @@ bool vfio_file_enforced_coherent(struct file *file)
 }
 EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
 
-static void vfio_device_file_set_kvm(struct file *file, struct kvm *kvm)
+static void vfio_device_file_set_kvm(struct file *file, struct kvm *kvm, struct module *kvm_module)
 {
 	struct vfio_device_file *df = file->private_data;
 
@@ -1494,6 +1502,7 @@ static void vfio_device_file_set_kvm(struct file *file, struct kvm *kvm)
 	 */
 	spin_lock(&df->kvm_ref_lock);
 	df->kvm = kvm;
+	df->kvm_module = kvm_module;
 	spin_unlock(&df->kvm_ref_lock);
 }
 
@@ -1505,16 +1514,16 @@ static void vfio_device_file_set_kvm(struct file *file, struct kvm *kvm)
  * When a VFIO device is first opened the KVM will be available in
  * device->kvm if one was associated with the file.
  */
-void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
+void vfio_file_set_kvm(struct file *file, struct kvm *kvm, struct module *kvm_module)
 {
 	struct vfio_group *group;
 
 	group = vfio_group_from_file(file);
 	if (group)
-		vfio_group_set_kvm(group, kvm);
+		vfio_group_set_kvm(group, kvm, kvm_module);
 
 	if (vfio_device_from_file(file))
-		vfio_device_file_set_kvm(file, kvm);
+		vfio_device_file_set_kvm(file, kvm, kvm_module);
 }
 EXPORT_SYMBOL_GPL(vfio_file_set_kvm);
 
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index e90859956514..69a8d527b0e8 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -53,6 +53,7 @@ struct vfio_device {
 	struct list_head dev_set_list;
 	unsigned int migration_flags;
 	struct kvm *kvm;
+	struct module *kvm_module;
 
 	/* Members below here are private, not for driver use */
 	unsigned int index;
@@ -339,7 +340,7 @@ static inline bool vfio_file_has_dev(struct file *file, struct vfio_device *devi
 #endif
 bool vfio_file_is_valid(struct file *file);
 bool vfio_file_enforced_coherent(struct file *file);
-void vfio_file_set_kvm(struct file *file, struct kvm *kvm);
+void vfio_file_set_kvm(struct file *file, struct kvm *kvm, struct module *kvm_module);
 
 #define VFIO_PIN_PAGES_MAX_ENTRIES	(PAGE_SIZE/sizeof(unsigned long))
 
diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
index 9f9acb66cc1e..515ed445d8e1 100644
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -37,13 +37,13 @@ struct kvm_vfio {
 
 static void kvm_vfio_file_set_kvm(struct file *file, struct kvm *kvm)
 {
-	void (*fn)(struct file *file, struct kvm *kvm);
+	void (*fn)(struct file *file, struct kvm *kvm, struct module *kvm_module);
 
 	fn = symbol_get(vfio_file_set_kvm);
 	if (!fn)
 		return;
 
-	fn(file, kvm);
+	fn(file, kvm, kvm ? THIS_MODULE : NULL);
 
 	symbol_put(vfio_file_set_kvm);
 }
-- 
2.53.0