Re: [PATCH 01/20] x86/tdx: Introduce tdvmcall_trampoline()

Dave Hansen
2024-05-17T15:21:39Z

On 5/17/24 07:19, Kirill A. Shutemov wrote:
> TDCALL calls are centralized into a few megawrappers that take the
> struct tdx_module_args as input. Most of the call sites only use a few
> arguments, but they have to zero out unused fields in the structure to
> avoid data leaks to the VMM. This leads to the compiler generating
> inefficient code: dozens of instructions per call site to clear unused
> fields of the structure.

I agree that this is what the silly compiler does in practice. But my
first preference for fixing it would just be an out-of-line memset() or
a pretty bare REP;MOV.

In other words, I think this as the foundational justification for the
rest of the series leaves a little to be desired.