virtio: bugfixes

Some small, obvious (in hindsight) bugfixes:
 
 - new ioctl in vhost-vdpa has a wrong # - not too late to fix
 
 - vhost has apparently been lacking an smp_rmb() -
   due to code duplication :( The duplication will be fixed in
   the next merge cycle, this is a minimal fix.
 
 - an error message in vhost talks about guest moving used index -
   which of course never happens, guest only ever moves the
   available index.
 
 - i2c-virtio didn't set the driver owner so it did not get
   refcounted correctly.
 
 Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

Pull virtio bugfixes from Michael Tsirkin:
 "Some small, obvious (in hindsight) bugfixes:

   - new ioctl in vhost-vdpa has a wrong # - not too late to fix

   - vhost has apparently been lacking an smp_rmb() - due to code
     duplication :( The duplication will be fixed in the next merge
     cycle, this is a minimal fix

   - an error message in vhost talks about guest moving used index -
     which of course never happens, guest only ever moves the available
     index

   - i2c-virtio didn't set the driver owner so it did not get refcounted
     correctly"

* tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost:
  vhost: correct misleading printing information
  vhost-vdpa: change ioctl # for VDPA_GET_VRING_SIZE
  virtio: store owner from modules with register_virtio_driver()
  vhost: Add smp_rmb() in vhost_enable_notify()
  vhost: Add smp_rmb() in vhost_vq_avail_empty()

Documentation/driver-api/virtio/writing_virtio_drivers.rst

@@ -97,7 +97,6 @@ like this::
 
 	static struct virtio_driver virtio_dummy_driver = {
 		.driver.name =  KBUILD_MODNAME,
-		.driver.owner = THIS_MODULE,
 		.id_table =     id_table,
 		.probe =        virtio_dummy_probe,
 		.remove =       virtio_dummy_remove,

drivers/vhost/vhost.c

@@ -2515,7 +2515,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 		vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
 
 		if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) {
-			vq_err(vq, "Guest moved used index from %u to %u",
+			vq_err(vq, "Guest moved avail index from %u to %u",
 				last_avail_idx, vq->avail_idx);
 			return -EFAULT;
 		}
@@ -2799,9 +2799,19 @@ bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 	r = vhost_get_avail_idx(vq, &avail_idx);
 	if (unlikely(r))
 		return false;
-	vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
 
-	return vq->avail_idx == vq->last_avail_idx;
+	vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
+	if (vq->avail_idx != vq->last_avail_idx) {
+		/* Since we have updated avail_idx, the following
+		 * call to vhost_get_vq_desc() will read available
+		 * ring entries. Make sure that read happens after
+		 * the avail_idx read.
+		 */
+		smp_rmb();
+		return false;
+	}
+
+	return true;
 }
 EXPORT_SYMBOL_GPL(vhost_vq_avail_empty);
 
@@ -2838,9 +2848,19 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 		       &vq->avail->idx, r);
 		return false;
 	}
-	vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
 
-	return vq->avail_idx != vq->last_avail_idx;
+	vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
+	if (vq->avail_idx != vq->last_avail_idx) {
+		/* Since we have updated avail_idx, the following
+		 * call to vhost_get_vq_desc() will read available
+		 * ring entries. Make sure that read happens after
+		 * the avail_idx read.
+		 */
+		smp_rmb();
+		return true;
+	}
+
+	return false;
 }
 EXPORT_SYMBOL_GPL(vhost_enable_notify);
 

drivers/virtio/virtio.c

@@ -362,14 +362,16 @@ static const struct bus_type virtio_bus = {
 	.remove = virtio_dev_remove,
 };
 
-int register_virtio_driver(struct virtio_driver *driver)
+int __register_virtio_driver(struct virtio_driver *driver, struct module *owner)
 {
 	/* Catch this early. */
 	BUG_ON(driver->feature_table_size && !driver->feature_table);
 	driver->driver.bus = &virtio_bus;
+	driver->driver.owner = owner;
+
 	return driver_register(&driver->driver);
 }
-EXPORT_SYMBOL_GPL(register_virtio_driver);
+EXPORT_SYMBOL_GPL(__register_virtio_driver);
 
 void unregister_virtio_driver(struct virtio_driver *driver)
 {

include/linux/virtio.h

@@ -170,7 +170,7 @@ size_t virtio_max_dma_size(const struct virtio_device *vdev);
 
 /**
  * struct virtio_driver - operations for a virtio I/O driver
- * @driver: underlying device driver (populate name and owner).
+ * @driver: underlying device driver (populate name).
  * @id_table: the ids serviced by this driver.
  * @feature_table: an array of feature numbers supported by this driver.
  * @feature_table_size: number of entries in the feature table array.
@@ -208,7 +208,10 @@ static inline struct virtio_driver *drv_to_virtio(struct device_driver *drv)
 	return container_of(drv, struct virtio_driver, driver);
 }
 
-int register_virtio_driver(struct virtio_driver *drv);
+/* use a macro to avoid include chaining to get THIS_MODULE */
+#define register_virtio_driver(drv) \
+	__register_virtio_driver(drv, THIS_MODULE)
+int __register_virtio_driver(struct virtio_driver *drv, struct module *owner);
 void unregister_virtio_driver(struct virtio_driver *drv);
 
 /* module_virtio_driver() - Helper macro for drivers that don't do

include/uapi/linux/vhost.h

@@ -179,12 +179,6 @@
 /* Get the config size */
 #define VHOST_VDPA_GET_CONFIG_SIZE	_IOR(VHOST_VIRTIO, 0x79, __u32)
 
-/* Get the count of all virtqueues */
-#define VHOST_VDPA_GET_VQS_COUNT	_IOR(VHOST_VIRTIO, 0x80, __u32)
-
-/* Get the number of virtqueue groups. */
-#define VHOST_VDPA_GET_GROUP_NUM	_IOR(VHOST_VIRTIO, 0x81, __u32)
-
 /* Get the number of address spaces. */
 #define VHOST_VDPA_GET_AS_NUM		_IOR(VHOST_VIRTIO, 0x7A, unsigned int)
 
@@ -228,10 +222,17 @@
 #define VHOST_VDPA_GET_VRING_DESC_GROUP	_IOWR(VHOST_VIRTIO, 0x7F,	\
 					      struct vhost_vring_state)
 
+
+/* Get the count of all virtqueues */
+#define VHOST_VDPA_GET_VQS_COUNT	_IOR(VHOST_VIRTIO, 0x80, __u32)
+
+/* Get the number of virtqueue groups. */
+#define VHOST_VDPA_GET_GROUP_NUM	_IOR(VHOST_VIRTIO, 0x81, __u32)
+
 /* Get the queue size of a specific virtqueue.
  * userspace set the vring index in vhost_vring_state.index
  * kernel set the queue size in vhost_vring_state.num
  */
-#define VHOST_VDPA_GET_VRING_SIZE	_IOWR(VHOST_VIRTIO, 0x80,	\
+#define VHOST_VDPA_GET_VRING_SIZE	_IOWR(VHOST_VIRTIO, 0x82,	\
 					      struct vhost_vring_state)
 #endif