AMO inst based on a mmio address will cause a store/amo access fault

[csgxiong]

Hi, I was doing some tests based on Rocket-chip. And I found AMO inst based on a mmio address would cause a store/amo access fault.
I checked the code and wave. The ppa_array and port_aa in TLB.scala will check the req.paddr and cause this error. I am confused by this behavior.
So does this behavior ruled by any specification?
Thanks.
B.R.