um: virtio_uml: query the number of vqs if supported

When the VHOST_USER_PROTOCOL_F_MQ protocol feature flag is set, we can
query the maximum number of virtual queues. Do so when supported and
extend the check to verify that we are not trying to allocate more
queues.

Signed-off-by: Benjamin Berg <[email protected]>
Link: https://patch.msgid.link/[email protected]
[add a message to the WARN_ON]
Signed-off-by: Johannes Berg <[email protected]>

1 files changed, 24 insertions, 1 deletions

diff --git a/arch/um/drivers/virtio_uml.c b/arch/um/drivers/virtio_uml.c
index 0f9efee4c671..cc3be48a9d6e 100644
--- a/arch/um/drivers/virtio_uml.c
+++ b/arch/um/drivers/virtio_uml.c
@@ -56,6 +56,7 @@ struct virtio_uml_device {
 	int sock, req_fd, irq;
 	u64 features;
 	u64 protocol_features;
+	u64 max_vqs;
 	u8 status;
 	u8 registered:1;
 	u8 suspended:1;
@@ -341,6 +342,17 @@ static int vhost_user_set_protocol_features(struct virtio_uml_device *vu_dev,
 				   protocol_features);
 }
 
+static int vhost_user_get_queue_num(struct virtio_uml_device *vu_dev,
+				    u64 *queue_num)
+{
+	int rc = vhost_user_send_no_payload(vu_dev, true,
+			VHOST_USER_GET_QUEUE_NUM);
+
+	if (rc)
+		return rc;
+	return vhost_user_recv_u64(vu_dev, queue_num);
+}
+
 static void vhost_user_reply(struct virtio_uml_device *vu_dev,
 			     struct vhost_user_msg *msg, int response)
 {
@@ -514,6 +526,15 @@ static int vhost_user_init(struct virtio_uml_device *vu_dev)
 			return rc;
 	}
 
+	if (vu_dev->protocol_features &
+			BIT_ULL(VHOST_USER_PROTOCOL_F_MQ)) {
+		rc = vhost_user_get_queue_num(vu_dev, &vu_dev->max_vqs);
+		if (rc)
+			return rc;
+	} else {
+		vu_dev->max_vqs = U64_MAX;
+	}
+
 	return 0;
 }
 
@@ -1018,7 +1039,9 @@ static int vu_find_vqs(struct virtio_device *vdev, unsigned nvqs,
 	struct virtqueue *vq;
 
 	/* not supported for now */
-	if (WARN_ON(nvqs > 64))
+	if (WARN(nvqs > 64 || nvqs > vu_dev->max_vqs,
+		 "%d VQs requested, only up to 64 or %lld supported\n",
+		 nvqs, vu_dev->max_vqs))
 		return -EINVAL;
 
 	rc = vhost_user_set_mem_table(vu_dev);