Are the values in context, independent of each other? ie does context[1] has any relation to context[0]? Padding is typically used when we want to uncover one token at a time (and hide the other tokens for the future).
If you’re simply inputting this sequence one at a time, you may not use a mask at all. Simply padding it with 0 values at the end, would let your model learn that these tokens (PAD tokens) are not useful. The softmax can still be applied and it should work just fine.