[PATCH v1 03/27] KVM, vfio: remove symbol_get(kvm_put_kvm) from vfio

[Steffen Eiden]

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

Right now, KVM and VFIO are using symbol_get to access each other's
symbols because of a circular reference between the modules, as well
as to avoid loading them unnecessarily.

The remaining use in VFIO is for kvm_put_kvm, which is not inline
because it needs to call kvm_destroy_vm.  However, storing the
address of kvm_destroy_vm in the "struct kvm" is enough to remove
the dependency from VFIO.

This also makes it possible to direct kvm_put_kvm to different
implementations of kvm_destroy_vm.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Steffen Eiden <seiden@xxxxxxxxxxxxx>
---
 drivers/vfio/vfio_main.c  | 29 +++++------------------------
 include/linux/kvm_host.h  |  1 -
 include/linux/kvm_types.h |  9 +++++++++
 include/linux/vfio.h      |  1 -
 virt/kvm/kvm_main.c       |  9 ++-------
 5 files changed, 16 insertions(+), 33 deletions(-)

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 42f515519d87..e9c6353c74d8 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -17,7 +17,7 @@
 #include <linux/idr.h>
 #include <linux/iommu.h>
 #if IS_ENABLED(CONFIG_KVM)
-#include <linux/kvm_host.h>
+#include <linux/kvm_types.h>
 #endif
 #include <linux/list.h>
 #include <linux/miscdevice.h>
@@ -436,9 +436,6 @@ EXPORT_SYMBOL_GPL(vfio_unregister_group_dev);
 void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm,
 			      struct module *kvm_module)
 {
-	void (*pfn)(struct kvm *kvm);
-	bool ret;
-
 	lockdep_assert_held(&device->dev_set->lock);
 
 	if (!kvm)
@@ -447,19 +444,10 @@ void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm,
 	if (!try_module_get(kvm_module))
 		return;
 
-	pfn = symbol_get(kvm_put_kvm);
-	if (WARN_ON(!pfn))
-		return;
-
-	ret = kvm_get_kvm_safe(kvm);
-	if (!ret) {
-		symbol_put(kvm_put_kvm);
-		return;
+	if (kvm_get_kvm_safe(kvm)) {
+		device->kvm = kvm;
+		device->kvm_module = kvm_module;
 	}
-
-	device->put_kvm = pfn;
-	device->kvm = kvm;
-	device->kvm_module = kvm_module;
 }
 
 void vfio_device_put_kvm(struct vfio_device *device)
@@ -469,15 +457,8 @@ void vfio_device_put_kvm(struct vfio_device *device)
 	if (!device->kvm)
 		return;
 
-	if (WARN_ON(!device->put_kvm))
-		goto clear;
-
-	device->put_kvm(device->kvm);
-	device->put_kvm = NULL;
-	symbol_put(kvm_put_kvm);
-
-clear:
 	module_put(device->kvm_module);
+	kvm_put_kvm(device->kvm);
 	device->kvm_module = NULL;
 	device->kvm = NULL;
 }
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index dc18ee99bba4..13f903993ed0 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1065,7 +1065,6 @@ static inline void kvm_irqfd_exit(void)
 int kvm_init(unsigned vcpu_size, unsigned vcpu_align, struct module *module);
 void kvm_exit(void);
 
-void kvm_put_kvm(struct kvm *kvm);
 bool file_is_kvm(struct file *file);
 void kvm_put_kvm_no_destroy(struct kvm *kvm);
 
diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
index add7cc2016e8..aadee536771a 100644
--- a/include/linux/kvm_types.h
+++ b/include/linux/kvm_types.h
@@ -144,6 +144,7 @@ struct kvm_vcpu_stat_generic {
 
 struct kvm_refcount {
 	refcount_t users_count;
+	void (*destroy)(struct kvm *kvm);
 };
 
 static inline void kvm_get_kvm(struct kvm *kvm)
@@ -164,6 +165,14 @@ static inline bool kvm_get_kvm_safe(struct kvm *kvm)
 	return refcount_inc_not_zero(&rc->users_count);
 }
 
+static inline void kvm_put_kvm(struct kvm *kvm)
+{
+	struct kvm_refcount *rc = (struct kvm_refcount *)kvm;
+
+	if (refcount_dec_and_test(&rc->users_count))
+		rc->destroy(kvm);
+}
+
 #endif /* !__ASSEMBLER__ */
 
 #endif /* __KVM_TYPES_H__ */
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 69a8d527b0e8..5c69532d6127 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -65,7 +65,6 @@ struct vfio_device {
 	unsigned int open_count;
 	struct completion comp;
 	struct iommufd_access *iommufd_access;
-	void (*put_kvm)(struct kvm *kvm);
 	struct inode *inode;
 #if IS_ENABLED(CONFIG_IOMMUFD)
 	struct iommufd_device *iommufd_device;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index cb5e01f92503..642f9e9638cc 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -120,6 +120,7 @@ static struct dentry *kvm_debugfs_dir;
 
 static const struct file_operations stat_fops_per_vm;
 
+static void kvm_destroy_vm(struct kvm *kvm);
 static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl,
 			   unsigned long arg);
 #ifdef CONFIG_KVM_COMPAT
@@ -1154,6 +1155,7 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
 		goto out_err_no_irq_routing;
 
 	refcount_set(&kvm->rc.users_count, 1);
+	kvm->rc.destroy = kvm_destroy_vm;
 
 	for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) {
 		for (j = 0; j < 2; j++) {
@@ -1316,13 +1318,6 @@ static void kvm_destroy_vm(struct kvm *kvm)
 	mmdrop(mm);
 }
 
-void kvm_put_kvm(struct kvm *kvm)
-{
-	if (refcount_dec_and_test(&kvm->rc.users_count))
-		kvm_destroy_vm(kvm);
-}
-EXPORT_SYMBOL_GPL(kvm_put_kvm);
-
 /*
  * Used to put a reference that was taken on behalf of an object associated
  * with a user-visible file descriptor, e.g. a vcpu or device, if installation
-- 
2.51.0