Re: [PATCH RFC 1/7] x86/virt/tdx: Add SEAMCALL wrapper to enter/exit TDX guest

[Adrian Hunter <adrian.hunter@intel.com>]

On 13/12/24 18:16, Dave Hansen wrote:
> On 12/11/24 10:43, Adrian Hunter wrote:
> ...
>> -	size = tdvmcall_a0_read(vcpu);
>> -	write = tdvmcall_a1_read(vcpu);
>> -	port = tdvmcall_a2_read(vcpu);
>> +	size  = tdx->vp_enter_out.io_size;
>> +	write = tdx->vp_enter_out.io_direction == TDX_WRITE;
>> +	port  = tdx->vp_enter_out.io_port;
> ...> +	case TDVMCALL_IO:
>> +		out->io_size		= args.r12;
>> +		out->io_direction	= args.r13 ? TDX_WRITE : TDX_READ;
>> +		out->io_port		= args.r14;
>> +		out->io_value		= args.r15;
>> +		break;
> 
> I honestly don't understand the need for the abstracted structure to sit
> in the middle. It doesn't get stored or serialized or anything, right?
> So why have _another_ structure?
> 
> Why can't this just be (for instance):
> 
> 	size = tdx->foo.r12;
> 
> ?
> 
> Basically, you hand around the raw arguments until you need to use them.

That sounds like what we have at present?  That is:

u64 tdh_vp_enter(u64 tdvpr, struct tdx_module_args *args)
{
	args->rcx = tdvpr;

	return __seamcall_saved_ret(TDH_VP_ENTER, args);
}

And then either add Rick's struct tdx_vp?  Like so:

u64 tdh_vp_enter(struct tdx_vp *vp, struct tdx_module_args *args)
{
	args->rcx = tdx_tdvpr_pa(vp);

	return __seamcall_saved_ret(TDH_VP_ENTER, args);
}

Or leave it to the caller:

u64 tdh_vp_enter(struct tdx_module_args *args)
{
	return __seamcall_saved_ret(TDH_VP_ENTER, args);
}

Or forget the wrapper altogether, and let KVM call
__seamcall_saved_ret() ?