Hello,

in any case the normal side OS depends on the TZ side, so whether the wish is honored or not does not really depend on this fast vs yield flag. Please adapt as you need, the filter is more of a precaution to avoid things going wrong unintentionally.

Adam

On Thu Jul 24, 2025 at 16:50:12 +0800, Gravel Yuan wrote:

Hello all,

I'm currently working on integrating OP-TEE support on the ARM64 architecture within the L4Re framework, specifically focusing on cryptographic operations such as encryption and decryption.

While reviewing the implementation, I noticed that in fiasco/src/kern/arm/smc_user.cpp, non-fast SMC calls are explicitly filtered out with the following check:

// only allow fast callsif (!(r0 & 0x80000000)) return commit_result(-L4_err::ENosys);

I'm trying to understand the rationale behind this design decision. Was it primarily driven by real-time performance requirements, or are there other considerations？

Additionally, as OP-TEE often uses *yielding calls* for certain operations, do you think it would be appropriate for us to consider extending the kernel to support such calls?

We would appreciate any insights or recommendations you can provide.