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

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Message-ID: <CAGtprH8AbW4P2t-wHVcTdfLwf3SJK5mxP1CbsMHTgMYEpLiWjQ@mail.gmail.com>
Date: Fri, 24 Oct 2025 17:54:40 -0700
From: Vishal Annapurve <vannapurve@...gle.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: dan.j.williams@...el.com, Chao Gao <chao.gao@...el.com>, 
	"Reshetova, Elena" <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>, 
	"Chatre, Reinette" <reinette.chatre@...el.com>, "Weiny, Ira" <ira.weiny@...el.com>, 
	"Huang, Kai" <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>, 
	"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 00/21] Runtime TDX Module update support

On Fri, Oct 24, 2025 at 2:19 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 10/24/25 14:12, dan.j.williams@...el.com wrote:
> >> The SGX solution, btw, was to at least ensure forward progress (CPUSVN
> >> update) when the last enclave goes away. So new enclaves aren't
> >> *prevented* from starting but the window when the first one starts
> >> (enclave count going from 0->1) is leveraged to do the update.
> > The status quo does ensure forward progress. The TD does get built and
> > the update does complete, just the small matter of TD attestation
> > failures, right?

I would think that it's not a "small" problem if confidential
workloads on the hosts are not able to pass attestation.

>
> Oh, yeah, for sure.
>
> If we do _nothing_ in the kernel (no build vs. module update
> synchronization), then the downside is being exposed to attestation
> failures if userspace either also does nothing or has bugs.
>
> That's actually, by far, my preferred solution to this whole mess:
> Userspace plays stupid games, userspace wins stupid prizes.
>

IIUC, enforcing "Avoid updates during update sensitive times" is not
that complex and will ensure to avoid any issues with user space
logic.