KVM: arm64: FFA: Release hyp rx buffer

According to the FF-A spec (Buffer states and ownership), after a
producer has written into a buffer, it is "full" and now owned by the
consumer. The producer won't be able to use that buffer, until the
consumer hands it over with an invocation such as RX_RELEASE.

It is clear in the following paragraph (Transfer of buffer ownership),
that MEM_RETRIEVE_RESP is transferring the ownership from producer (in
our case SPM) to consumer (hypervisor). RX_RELEASE is therefore
mandatory here.

It is less clear though what is happening with MEM_FRAG_TX. But this
invocation, as a response to MEM_FRAG_RX writes into the same hypervisor
RX buffer (see paragraph "Transmission of transaction descriptor in
fragments"). Also this is matching the TF-A implementation where the RX
buffer is marked "full" during a MEM_FRAG_RX.

Release the RX hypervisor buffer in those two cases. This will unblock
later invocations using this buffer which would otherwise fail.
(RETRIEVE_REQ, MEM_FRAG_RX and PARTITION_INFO_GET).

Signed-off-by: Vincent Donnefort <[email protected]>
Reviewed-by: Sudeep Holla <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Marc Zyngier <[email protected]>

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