Re: [PATCH v36 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call

[Andy Lutomirski]

On Thu, Aug 6, 2020 at 7:55 AM Nathaniel McCallum <npmccallum@xxxxxxxxxx> wrote:
>
> In a past revision of this patch, I had requested a void *misc
> parameter that could be passed through vdso_sgx_enter_enclave_t into
> sgx_enclave_exit_handler_t. This request encountered some push back
> and I dropped the issue. However, I'd like to revisit it or something
> similar.

Why do you need an exit handler at all?  IIRC way back when I
suggested that we simply not support it at all.  If you want to
call__vdso_sgx_enter_enclave() in a loop, call it in a loop.  If you
want to wrap it intelligently in Rust, you don't want a callback
anyway -- that forces you have an FFI (or non-Rust, anyway) frame on
the stack, which interacts poorly with panic handling and prevents you
from using await in your Rust callback handler.  If, on the other
hand, you just call __vdso_sg_enter_enclave() in a loop, all these
problems go away and, if you really want, you can pass in a callback
in Rust and call the callback from Rust.

What am I missing?  I still don't really understand why we are
supporting this mechanism at all.  Just the asm code to invoke the
callback seems to be about half of the entire function.