linux-kernel - Re: [PATCH v3 05/26] coco/tdx-host: Expose TDX Module version

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Message-ID: <aXtpqefDbfW/HCWW@intel.com>
Date: Thu, 29 Jan 2026 22:07:37 +0800
From: Chao Gao <chao.gao@...el.com>
To: Dave Hansen <dave.hansen@...el.com>
CC: <linux-coco@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<kvm@...r.kernel.org>, <x86@...nel.org>, <reinette.chatre@...el.com>,
	<ira.weiny@...el.com>, <kai.huang@...el.com>, <dan.j.williams@...el.com>,
	<yilun.xu@...ux.intel.com>, <sagis@...gle.com>, <vannapurve@...gle.com>,
	<paulmck@...nel.org>, <nik.borisov@...e.com>, <zhenzhong.duan@...el.com>,
	<seanjc@...gle.com>, <rick.p.edgecombe@...el.com>, <kas@...nel.org>,
	<dave.hansen@...ux.intel.com>, <vishal.l.verma@...el.com>
Subject: Re: [PATCH v3 05/26] coco/tdx-host: Expose TDX Module version

On Wed, Jan 28, 2026 at 09:01:35AM -0800, Dave Hansen wrote:
>On 1/23/26 06:55, Chao Gao wrote:
>...
>> This approach follows the pattern used by microcode updates and
>> other CoCo implementations:
>> 
>> 1. AMD has a PCI device for the PSP for SEV which provides an
>> existing place to hang their equivalent metadata.
>> 
>> 2. ARM CCA will likely have a faux device (although it isn't obvious
>> if they have a need to export version information there) [1]
>> 
>> 3. Microcode revisions are exposed as CPU device attributes
>
>I kinda disagree with the idea that this follows existing patterns. It
>uses a *NEW* pattern.
>
>AMD doesn't use a faux device because they *HAVE* a PCI device in their
>architecture. TDX doesn't have a PCI device in its hardware architecture.
>
>ARM CCA doesn't exist in the tree.
>
>CPU microcode doesn't use a faux device. For good reason. The microcode
>version is *actually* per-cpu. It can differ between CPU cores. The TDX
>module version is not per-cpu. There's one and only one global module.
>This is the reason that we need a global, unique device for TDX.
>
>I'm not saying that being new is a bad thing. But let's not pretend this
>is following any kind of existing pattern. Let's explain *why* it needs
>to be different.

Thanks. I understand your point. The pattern I was referring to is: using a
device (PCI device, virtual device, or faux device) and exposing
versions/metadata as device attributes.

You're right if we look at the details, they're not exactly the same pattern.
I'll revise the changelog to make this clearer.