Why had Soviet Union always sided with India?

Soviet Union and present day Russia is always regarded as close ally of India.
It is well demonstrated by the 6 Soviet vetoed UN resolutions against India.
Even when India declared it's policy of non-alignment since it's formation and being a non-communist nation, during the 1962 India-China war Soviet Union under Nikita Khrushchev went forward as far as openly condemning Mao's China which always strived to make alliance with the Soviets since it's formation.

What philosophy or reasoning drove Soviet Union to side with India?