[PATCH v4 01/27] VFIO: take reference to the KVM module

[Steffen Eiden <seiden@linux.ibm.com>]

From: 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>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Acked-by: Alex Williamson <alex@shazbot.org>
---
 drivers/vfio/device_cdev.c |  2 +-
 drivers/vfio/group.c       |  5 +++--
 drivers/vfio/vfio.h        | 15 ++++++++++-----
 drivers/vfio/vfio_main.c   | 38 ++++++++++++++++++++++++--------------
 include/linux/vfio.h       |  3 ++-
 virt/kvm/vfio.c            |  4 ++--
 6 files changed, 42 insertions(+), 25 deletions(-)

diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
index 54abf312cf04..a729be99d06c 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 b2299e5bc6df..fc24c0b2cc6f 100644
--- a/drivers/vfio/group.c
+++ b/drivers/vfio/group.c
@@ -163,7 +163,7 @@ 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);
 }
 
@@ -860,10 +860,11 @@ 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 e4b72e79b7e3..8209da17246c 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 iommufd_ctx		*iommufd;
 	spinlock_t			kvm_ref_lock;
@@ -107,7 +109,7 @@ 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);
@@ -170,7 +172,8 @@ 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)
 {
 }
 
@@ -434,11 +437,13 @@ 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 ed538aebb0b8..8289aca97b6b 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -448,7 +448,8 @@ 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);
@@ -459,25 +460,31 @@ void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm)
 	if (!kvm)
 		return;
 
+	if (!try_module_get(kvm_module))
+		return;
+
 	pfn = symbol_get(kvm_put_kvm);
 	if (WARN_ON(!pfn))
-		return;
+		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)
@@ -496,6 +503,8 @@ void vfio_device_put_kvm(struct vfio_device *device)
 
 clear:
 	device->kvm = NULL;
+	module_put(device->kvm_module);
+	device->kvm_module = NULL;
 }
 #endif
 
@@ -1520,7 +1529,7 @@ 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;
 
@@ -1531,6 +1540,7 @@ 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);
 }
 
@@ -1542,16 +1552,16 @@ 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 31b826efba00..5bfec0339804 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -55,6 +55,7 @@ struct vfio_device {
 	unsigned int migration_flags;
 	u8 precopy_info_v2;
 	struct kvm *kvm;
+	struct module *kvm_module;
 
 	/* Members below here are private, not for driver use */
 	unsigned int index;
@@ -377,7 +378,7 @@ 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 6cdc4e9a333a..c593f31136f9 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