[PATCH v2 01/28] VFIO: take reference to the KVM module

Steffen Eiden
2026-04-28T16:02:07Z

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 | 37 +++++++++++++++++++++++--------------
include/linux/vfio.h | 3 ++-
virt/kvm/vfio.c | 4 ++--
6 files changed, 41 insertions(+), 25 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;

+ 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)
@@ -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);
}
--
2.51.0