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

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Message-ID: <f7cd9af3-8b6a-4984-80ef-e9129d8d94bd@intel.com>
Date: Fri, 13 Dec 2024 18:30:09 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Dave Hansen <dave.hansen@...el.com>, pbonzini@...hat.com,
 seanjc@...gle.com, kvm@...r.kernel.org, dave.hansen@...ux.intel.com
Cc: rick.p.edgecombe@...el.com, kai.huang@...el.com,
 reinette.chatre@...el.com, xiaoyao.li@...el.com,
 tony.lindgren@...ux.intel.com, binbin.wu@...ux.intel.com,
 dmatlack@...gle.com, isaku.yamahata@...el.com, nik.borisov@...e.com,
 linux-kernel@...r.kernel.org, x86@...nel.org, yan.y.zhao@...el.com,
 chao.gao@...el.com, weijiang.yang@...el.com
Subject: Re: [PATCH RFC 1/7] x86/virt/tdx: Add SEAMCALL wrapper to enter/exit
 TDX guest

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() ?