vfio/virtio: Convert list_lock from spinlock to mutex

The list_lock spinlock with IRQ disabling was copied from the mlx5
vfio-pci variant driver, where it is justified by a hardirq async
command completion callback that accesses the protected lists.  The
virtio driver has no such interrupt context usage; all list_lock
acquisitions occur in process context via file read/write operations
or state transitions under state_mutex.

Convert list_lock to a mutex to be consistent with peer vfio-pci
variant drivers (hisilicon, pds, qat, xe) which all use mutexes for
equivalent migration data protection.  This also fixes a mismatched
spin_lock()/spin_unlock_irq() pair in virtiovf_read_device_context_chunk()
that could incorrectly enable interrupts.

Reported-by: Jinhui Guo <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]
Fixes: 0bbc82e ("vfio/virtio: Add support for the basic live migration functionality")
Cc: [email protected]
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Alex Williamson <[email protected]>
Reviewed-by: Yishai Hadas <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alex Williamson <[email protected]>

Author: Alex Williamson

drivers/vfio/pci/virtio/common.h

@@ -68,7 +68,7 @@ struct virtiovf_migration_file {
 	enum virtiovf_migf_state state;
 	enum virtiovf_load_state load_state;
 	/* synchronize access to the lists */
-	spinlock_t list_lock;
+	struct mutex list_lock;
 	struct list_head buf_list;
 	struct list_head avail_list;
 	struct virtiovf_data_buffer *buf;

drivers/vfio/pci/virtio/migrate.c

@@ -142,9 +142,9 @@ virtiovf_alloc_data_buffer(struct virtiovf_migration_file *migf, size_t length)
 
 static void virtiovf_put_data_buffer(struct virtiovf_data_buffer *buf)
 {
-	spin_lock_irq(&buf->migf->list_lock);
+	mutex_lock(&buf->migf->list_lock);
 	list_add_tail(&buf->buf_elm, &buf->migf->avail_list);
-	spin_unlock_irq(&buf->migf->list_lock);
+	mutex_unlock(&buf->migf->list_lock);
 }
 
 static int
@@ -170,21 +170,21 @@ virtiovf_get_data_buffer(struct virtiovf_migration_file *migf, size_t length)
 
 	INIT_LIST_HEAD(&free_list);
 
-	spin_lock_irq(&migf->list_lock);
+	mutex_lock(&migf->list_lock);
 	list_for_each_entry_safe(buf, temp_buf, &migf->avail_list, buf_elm) {
 		list_del_init(&buf->buf_elm);
 		if (buf->allocated_length >= length) {
-			spin_unlock_irq(&migf->list_lock);
+			mutex_unlock(&migf->list_lock);
 			goto found;
 		}
 		/*
 		 * Prevent holding redundant buffers. Put in a free
-		 * list and call at the end not under the spin lock
+		 * list and call at the end not under the mutex
 		 * (&migf->list_lock) to minimize its scope usage.
 		 */
 		list_add(&buf->buf_elm, &free_list);
 	}
-	spin_unlock_irq(&migf->list_lock);
+	mutex_unlock(&migf->list_lock);
 	buf = virtiovf_alloc_data_buffer(migf, length);
 
 found:
@@ -295,6 +295,7 @@ static int virtiovf_release_file(struct inode *inode, struct file *filp)
 	struct virtiovf_migration_file *migf = filp->private_data;
 
 	virtiovf_disable_fd(migf);
+	mutex_destroy(&migf->list_lock);
 	mutex_destroy(&migf->lock);
 	kfree(migf);
 	return 0;
@@ -308,7 +309,7 @@ virtiovf_get_data_buff_from_pos(struct virtiovf_migration_file *migf,
 	bool found = false;
 
 	*end_of_data = false;
-	spin_lock_irq(&migf->list_lock);
+	mutex_lock(&migf->list_lock);
 	if (list_empty(&migf->buf_list)) {
 		*end_of_data = true;
 		goto end;
@@ -329,7 +330,7 @@ virtiovf_get_data_buff_from_pos(struct virtiovf_migration_file *migf,
 	migf->state = VIRTIOVF_MIGF_STATE_ERROR;
 
 end:
-	spin_unlock_irq(&migf->list_lock);
+	mutex_unlock(&migf->list_lock);
 	return found ? buf : NULL;
 }
 
@@ -369,10 +370,10 @@ static ssize_t virtiovf_buf_read(struct virtiovf_data_buffer *vhca_buf,
 	}
 
 	if (*pos >= vhca_buf->start_pos + vhca_buf->length) {
-		spin_lock_irq(&vhca_buf->migf->list_lock);
+		mutex_lock(&vhca_buf->migf->list_lock);
 		list_del_init(&vhca_buf->buf_elm);
 		list_add_tail(&vhca_buf->buf_elm, &vhca_buf->migf->avail_list);
-		spin_unlock_irq(&vhca_buf->migf->list_lock);
+		mutex_unlock(&vhca_buf->migf->list_lock);
 	}
 
 	return done;
@@ -549,9 +550,9 @@ virtiovf_add_buf_header(struct virtiovf_data_buffer *header_buf,
 	header_buf->length = sizeof(header);
 	header_buf->start_pos = header_buf->migf->max_pos;
 	migf->max_pos += header_buf->length;
-	spin_lock_irq(&migf->list_lock);
+	mutex_lock(&migf->list_lock);
 	list_add_tail(&header_buf->buf_elm, &migf->buf_list);
-	spin_unlock_irq(&migf->list_lock);
+	mutex_unlock(&migf->list_lock);
 	return 0;
 }
 
@@ -616,9 +617,9 @@ virtiovf_read_device_context_chunk(struct virtiovf_migration_file *migf,
 
 	buf->start_pos = buf->migf->max_pos;
 	migf->max_pos += buf->length;
-	spin_lock(&migf->list_lock);
+	mutex_lock(&migf->list_lock);
 	list_add_tail(&buf->buf_elm, &migf->buf_list);
-	spin_unlock_irq(&migf->list_lock);
+	mutex_unlock(&migf->list_lock);
 	return 0;
 
 out_header:
@@ -687,7 +688,7 @@ virtiovf_pci_save_device_data(struct virtiovf_pci_core_device *virtvdev,
 	mutex_init(&migf->lock);
 	INIT_LIST_HEAD(&migf->buf_list);
 	INIT_LIST_HEAD(&migf->avail_list);
-	spin_lock_init(&migf->list_lock);
+	mutex_init(&migf->list_lock);
 	migf->virtvdev = virtvdev;
 
 	lockdep_assert_held(&virtvdev->state_mutex);
@@ -1077,7 +1078,7 @@ virtiovf_pci_resume_device_data(struct virtiovf_pci_core_device *virtvdev)
 	mutex_init(&migf->lock);
 	INIT_LIST_HEAD(&migf->buf_list);
 	INIT_LIST_HEAD(&migf->avail_list);
-	spin_lock_init(&migf->list_lock);
+	mutex_init(&migf->list_lock);
 
 	buf = virtiovf_alloc_data_buffer(migf, VIRTIOVF_TARGET_INITIAL_BUF_SIZE);
 	if (IS_ERR(buf)) {