ARMv8 : How Cache Handling at EL3 is different to that of Cache handling in EL1 (NS=0)?

Scenario:

Sent a buffer reference and its size from EL1 secure world as a SIP SMC, such that EL3 write on that buffer and ERET to EL1.

Query: 

1. Does cache flush is required at any exception level to correct read the buffer at EL1 after ERET ?

2. If Yes, Why?

3. If no, then where to fetch related information that explains in detail why it is not required.