@flohack Source was from https://www.techarp.com/guides/complete-meltdown-spectre-cpu-list/4/
I have concluded that only MX4 and Nexus 4 are affected.
However, I didn't know that the MX4 was affected and probably the Nexus 4. It means, almost all core smartphones compatible with UBports are affected by Meltdown/Spectre (it is a big concern). I hope another A53 smartphone will be in the core list in the future, despite the fact that I know it is far from easy to port UBports on new devices.
By the way, it seems that Snapdragon 400 is made with 4x ARM Cortex-A7. Could somebody confirm it ? Because, it would mean that Moto G 2014 can be not affected. Thank you. Source : https://www.gsmarena.com/motorola_moto_g_2014-review-1139p5.php