linux-kernel - Re: [PATCH v12 08/22] x86/virt/tdx: Get information about TDX module and TDX-capable memory

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Date:   Wed, 28 Jun 2023 16:10:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kai Huang <kai.huang@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, dave.hansen@...el.com,
        kirill.shutemov@...ux.intel.com, tony.luck@...el.com,
        tglx@...utronix.de, bp@...en8.de, mingo@...hat.com, hpa@...or.com,
        seanjc@...gle.com, pbonzini@...hat.com, david@...hat.com,
        dan.j.williams@...el.com, rafael.j.wysocki@...el.com,
        ashok.raj@...el.com, reinette.chatre@...el.com,
        len.brown@...el.com, ak@...ux.intel.com, isaku.yamahata@...el.com,
        ying.huang@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, nik.borisov@...e.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v12 08/22] x86/virt/tdx: Get information about TDX module
 and TDX-capable memory

On Tue, Jun 27, 2023 at 02:12:38AM +1200, Kai Huang wrote:
> +static int tdx_get_sysinfo(struct tdsysinfo_struct *sysinfo,
> +			   struct cmr_info *cmr_array)
> +{
> +	struct tdx_module_output out;
> +	u64 sysinfo_pa, cmr_array_pa;
> +	int ret;
> +
> +	sysinfo_pa = __pa(sysinfo);
> +	cmr_array_pa = __pa(cmr_array);
> +	ret = seamcall(TDH_SYS_INFO, sysinfo_pa, TDSYSINFO_STRUCT_SIZE,
> +			cmr_array_pa, MAX_CMRS, NULL, &out);
> +	if (ret)
> +		return ret;
> +
> +	pr_info("TDX module: attributes 0x%x, vendor_id 0x%x, major_version %u, minor_version %u, build_date %u, build_num %u",
> +		sysinfo->attributes,	sysinfo->vendor_id,
> +		sysinfo->major_version, sysinfo->minor_version,
> +		sysinfo->build_date,	sysinfo->build_num);
> +
> +	/* R9 contains the actual entries written to the CMR array. */

So I'm vexed by this comment; it's either not enough or too much.

I mean, as given you assume we all know about the magic parameters to
TDH_SYS_INFO but then somehow need an explanation for how %r9 is changed
from the array size to the number of used entries.

Either describe the whole thing or none of it.

Me, I would prefer all of it, because I've no idea where to begin
looking for any of this, SDM doesn't seem to be the place. That doesn't
even list TDCALL/SEAMCALL in Volume 2 :-( Let alone describe the magic
values.

> +	print_cmrs(cmr_array, out.r9);
> +
> +	return 0;
> +}