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 <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20241103212854.1436046-5-benjamin@sipsolutions.net
[add a message to the WARN_ON]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: benzea

arch/um/drivers/vhost_user.h

@@ -10,6 +10,7 @@
 /* Feature bits */
 #define VHOST_USER_F_PROTOCOL_FEATURES	30
 /* Protocol feature bits */
+#define VHOST_USER_PROTOCOL_F_MQ			0
 #define VHOST_USER_PROTOCOL_F_REPLY_ACK			3
 #define VHOST_USER_PROTOCOL_F_SLAVE_REQ			5
 #define VHOST_USER_PROTOCOL_F_CONFIG			9
@@ -23,7 +24,8 @@
 /* Supported transport features */
 #define VHOST_USER_SUPPORTED_F		BIT_ULL(VHOST_USER_F_PROTOCOL_FEATURES)
 /* Supported protocol features */
-#define VHOST_USER_SUPPORTED_PROTOCOL_F	(BIT_ULL(VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
+#define VHOST_USER_SUPPORTED_PROTOCOL_F	(BIT_ULL(VHOST_USER_PROTOCOL_F_MQ) | \
+					 BIT_ULL(VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
 					 BIT_ULL(VHOST_USER_PROTOCOL_F_SLAVE_REQ) | \
 					 BIT_ULL(VHOST_USER_PROTOCOL_F_CONFIG) | \
 					 BIT_ULL(VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS))

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);