vhost-vdpa: clean iotlb map during reset for older userspace

Using .compat_reset op from the previous patch, the buggy .reset
behaviour can be kept as-is on older userspace apps, which don't ack the
IOTLB_PERSIST backend feature. As this compatibility quirk is limited to
those drivers that used to be buggy in the past, it won't affect change
the behaviour or affect ABI on the setups with API compliant driver.

The separation of .compat_reset from the regular .reset allows
vhost-vdpa able to know which driver had broken behaviour before, so it
can apply the corresponding compatibility quirk to the individual driver
whenever needed. Compared to overloading the existing .reset with
flags, .compat_reset won't cause any extra burden to the implementation
of every compliant driver.

[mst: squashed in two fixup commits]

Message-Id: <[e-mail]>
Message-Id: <[e-mail]>
Reported-by: Dragos Tatulea <[e-mail]>
Tested-by: Dragos Tatulea <[e-mail]>
Message-Id: <[e-mail]>
Reported-by: Lei Yang <[e-mail]>
Signed-off-by: Si-Wei Liu <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>
Tested-by: Lei Yang <[e-mail]>

drivers/vhost/vdpa.c

···
 	irq_bypass_unregister_producer(&vq->call_ctx.producer);
 }
 
-static int vhost_vdpa_reset(struct vhost_vdpa *v)
+static int _compat_vdpa_reset(struct vhost_vdpa *v)
 {
 	struct vdpa_device *vdpa = v->vdpa;
+	u32 flags = 0;
 
+	if (v->vdev.vqs) {
+		flags |= !vhost_backend_has_feature(v->vdev.vqs[0],
+						    VHOST_BACKEND_F_IOTLB_PERSIST) ?
+			 VDPA_RESET_F_CLEAN_MAP : 0;
+	}
+
+	return vdpa_reset(vdpa, flags);
+}
+
+static int vhost_vdpa_reset(struct vhost_vdpa *v)
+{
 	v->in_batch = 0;
-
-	return vdpa_reset(vdpa);
+	return _compat_vdpa_reset(v);
 }
 
 static long vhost_vdpa_bind_mm(struct vhost_vdpa *v)
···
 			vhost_vdpa_unsetup_vq_irq(v, i);
 
 	if (status == 0) {
-		ret = vdpa_reset(vdpa);
+		ret = _compat_vdpa_reset(v);
 		if (ret)
 			return ret;
 	} else
···
 	vhost_vdpa_free_domain(v);
 	vhost_dev_cleanup(&v->vdev);
 	kfree(v->vdev.vqs);
+	v->vdev.vqs = NULL;
 }
 
 static int vhost_vdpa_open(struct inode *inode, struct file *filep)

drivers/virtio/virtio_vdpa.c

···
 {
 	struct vdpa_device *vdpa = vd_get_vdpa(vdev);
 
-	vdpa_reset(vdpa);
+	vdpa_reset(vdpa, 0);
 }
 
 static bool virtio_vdpa_notify(struct virtqueue *vq)

include/linux/vdpa.h

···
 	return vdev->dma_dev;
 }
 
-static inline int vdpa_reset(struct vdpa_device *vdev)
+static inline int vdpa_reset(struct vdpa_device *vdev, u32 flags)
 {
 	const struct vdpa_config_ops *ops = vdev->config;
 	int ret;
 
 	down_write(&vdev->cf_lock);
 	vdev->features_valid = false;
-	ret = ops->reset(vdev);
+	if (ops->compat_reset && flags)
+		ret = ops->compat_reset(vdev, flags);
+	else
+		ret = ops->reset(vdev);
 	up_write(&vdev->cf_lock);
 	return ret;
 }