vhost-vdpa: free iommu domain after last use during cleanup

Currently vhost_vdpa_cleanup() unmaps the DMA mappings by calling
`iommu_unmap(v->domain, map->start, map->size);`
from vhost_vdpa_general_unmap() when the parent vDPA driver doesn't
provide DMA config operations.

However, the IOMMU domain referred to by `v->domain` is freed in
vhost_vdpa_free_domain() before vhost_vdpa_cleanup() in
vhost_vdpa_release() which results in NULL pointer de-reference.
Accordingly, moving the call to vhost_vdpa_free_domain() in
vhost_vdpa_cleanup() would makes sense. This will also help
detaching the dma device in error handling of vhost_vdpa_alloc_domain().

This issue was observed on terminating QEMU with SIGQUIT.

Fixes: 037d430 ("vhost-vdpa: call vhost_vdpa_cleanup during the release")
Signed-off-by: Gautam Dawar <gautam.dawar@amd.com>
Message-Id: <20230301163203.29883-1-gautam.dawar@amd.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

Author: gdawar-xilinx

drivers/vhost/vdpa.c

@@ -1169,6 +1169,7 @@ static int vhost_vdpa_alloc_domain(struct vhost_vdpa *v)
 
 err_attach:
 	iommu_domain_free(v->domain);
+	v->domain = NULL;
 	return ret;
 }
 
@@ -1213,6 +1214,7 @@ static void vhost_vdpa_cleanup(struct vhost_vdpa *v)
 			vhost_vdpa_remove_as(v, asid);
 	}
 
+	vhost_vdpa_free_domain(v);
 	vhost_dev_cleanup(&v->vdev);
 	kfree(v->vdev.vqs);
 }
@@ -1285,7 +1287,6 @@ static int vhost_vdpa_release(struct inode *inode, struct file *filep)
 	vhost_vdpa_clean_irq(v);
 	vhost_vdpa_reset(v);
 	vhost_dev_stop(&v->vdev);
-	vhost_vdpa_free_domain(v);
 	vhost_vdpa_config_put(v);
 	vhost_vdpa_cleanup(v);
 	mutex_unlock(&d->mutex);