Re: [PATCHv4 04/30] x86/tdx: Add __tdx_module_call() and __tdx_hypercall() helper functions

[Dave Hansen]

On 2/24/22 07:56, Kirill A. Shutemov wrote:
> +	tdcall
> +
> +	/*
> +	 * TDVMCALL leaf does not suppose to fail. If it fails something
> +	 * is horribly wrong with TDX module. Stop the world.
> +	 */
> +	testq %rax, %rax
> +	jne .Lpanic

This should be:

	"A TDVMCALL is not supposed to fail."

I also wish this was mentioning something about the difference between a
failure and return code.

	/*
	 * %rax==0 indicates a failure of the TDVMCALL mechanism itself
	 * and that something has gone horribly wrong with the TDX
	 * module.
	 *
	 * The return status of the hypercall operation is separate
	 * (in %r10).  Hypercall errors are a part of normal operation
	 * and are handled by callers.
	 */

I've been confused by this exact thing multiple times over the months
that I've been looking at this code.  I think it deserves a good comment.