linux-kernel - Re: [PATCH v2 00/21] Runtime TDX Module update support

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Message-ID: <6901792e39d13_10e9100ed@dwillia2-mobl4.notmuch>
Date: Tue, 28 Oct 2025 19:17:18 -0700
From: <dan.j.williams@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Erdem Aktas
	<erdemaktas@...gle.com>
CC: <dan.j.williams@...el.com>, Vishal Annapurve <vannapurve@...gle.com>,
	"Dave Hansen" <dave.hansen@...el.com>, Chao Gao <chao.gao@...el.com>, "Elena
 Reshetova" <elena.reshetova@...el.com>, "linux-coco@...ts.linux.dev"
	<linux-coco@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, "Reinette
 Chatre" <reinette.chatre@...el.com>, Ira Weiny <ira.weiny@...el.com>, "Kai
 Huang" <kai.huang@...el.com>, "yilun.xu@...ux.intel.com"
	<yilun.xu@...ux.intel.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"paulmck@...nel.org" <paulmck@...nel.org>, "nik.borisov@...e.com"
	<nik.borisov@...e.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar
	<mingo@...hat.com>, "Kirill A. Shutemov" <kas@...nel.org>, Paolo Bonzini
	<pbonzini@...hat.com>, Rick P Edgecombe <rick.p.edgecombe@...el.com>, "Thomas
 Gleixner" <tglx@...utronix.de>
Subject: Re: [PATCH v2 00/21] Runtime TDX Module update support

Sean Christopherson wrote:
[..]
> > IMO, It is something userspace should decide, kernel's job is to
> > provide the necessary interface about it.
> 
> I disagree, I don't think userspace should even get the option.  IMO, not setting
> AVOID_COMPAT_SENSITIVE is all kinds of crazy.

Do see Table 4.4: "Comparison of Update Incompatibility Detection and/or
Avoidance Methods" from the latest base architecture specification [1].
It lists out the pros and cons of not setting AVOID_COMPAT_SENSITIVE.
This thread has only argued the merits of "None" and "Avoid updates
during update- sensitive times". It has not discussed "Detect
incompatibility after update", but let us not do that. You can just
assume the Module has multiple solutions to this awkward problem
precisely because different VMMs came to different conclusions.

I want this thread to end so I am not going to argue past what Dave and
Sean want to do here.

[1]: https://www.intel.com/content/www/us/en/content-details/865787/intel-tdx-module-base-architecture-specification.html