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Isn't it buggy? >> > >> >Caller expects to see field_id == -1 to exit loop, but you never set it >> >in case of an error. It will result in endless loop if error happens not on >> >the first iteration. >> >> The caller checks the return value and bails out if there was an error. > >I misread it. Missed the break. > >> > >> >Drop the branch and always return ret. >> >> Setting field_id to -1 on error appears unnecessary since callers must check >> the return value anyway. And, even if args.r8 were copied to field_id >> on error, this wouldn't guarantee that field_id would be set to -1, as >> SEAMCALLs may encounter #GP/#UD exceptions where r8 remains unchanged. >> >> Given this, I prefer to leave field_id as an undefined value on error, and >> callers should not read/use it when an error occurs. > >It is not undefined. TDX module sets R8 to -1 in case of error. Yes, I saw it. That's TDX module ABI. It doesn't necessarily have to be the semantics of this kernel API. So, we have two choices: 1. Follow the TDX module, i.e., set field_id to -1 on error. Then we should do: if (ret) *field_id = -1; else *field_id = args.r8; to cover #GP/#UD cases. 2. Leave field_id undefined on error, as in this patch. I don't see the value of setting field_id to -1 on error if callers are expected to check the return value.