On Wed, 22 Jul 2020 at 15:01, Olivier Deprez via Hafnium < hafnium@lists.trustedfirmware.org> wrote:

Hi,

We noticed api_ffa_features returns FFA_SUCCESS_32 for all implemented ABIs with the SMC32 convention, but FFA_RXTX_MAP_64: https://git.trustedfirmware.org/hafnium/hafnium.git/tree/src/api.c#n1430

On the other hand ffa_handler discards the SMC convention bit:

https://git.trustedfirmware.org/hafnium/hafnium.git/tree/src/arch/aarch64/hy...

It means one can call FFA_FEATURES(FFA_RXTX_MAP_32) which will fail, although this does not prevent effectively calling the same ABI with the SMC32 convention.

Is there some fine tuning to do here? Should we just discard the SMC convention bit in api_ffa_features?

I don't think FFA_RXTX_MAP_32 will work, because we need 64-bit addresses for the buffers that it passes. We should probably return an error from ffa_handler if a VM tries to call FFA_RXTX_MAP_32.

For other functions I guess we could make it support either, by discarding the SMC convention bit in FFA_FEATURES as you suggest. Are there any other differences between the SMC32 and SMC64 convention which we need to take care of?