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

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Message-ID: <CAGtprH93h_f11-mBRExr7xwN284Otnk6vi9R-b5PfVtL+wvXaQ@mail.gmail.com>
Date: Wed, 15 Oct 2025 07:19:01 -0700
From: Vishal Annapurve <vannapurve@...gle.com>
To: "Reshetova, Elena" <elena.reshetova@...el.com>
Cc: "Gao, Chao" <chao.gao@...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>, "Williams, Dan J" <dan.j.williams@...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 Wed, Oct 15, 2025 at 1:54 AM Reshetova, Elena
<elena.reshetova@...el.com> wrote:
>
>
> > On Tue, Sep 30, 2025 at 7:54 PM Chao Gao <chao.gao@...el.com> wrote:
> > >
> > > === TDX Module Distribution Model ===
> > >
> > > At a high level, Intel publishes all TDX Modules on the github [2], along
> > > with a mapping_file.json which documents the compatibility information
> > > about each TDX Module and a userspace tool to install the TDX Module. OS
> >
> > [2] mentions about a limitation of doing runtime TDX module update:
> >
> > "Performing TD Preserving during a TD Build operation might result in
> > a corrupted TD hash in the TD attestation report. Until fixed in a
> > future Intel TDX module update, a host VMM can avoid the problem by
> > not conducting a TD Preserving Update while TD Build operation is in
> > progress."
> >
> > Do you know if this issue is fixed already? If so, what version of TDX
> > module fixes this issue?
>
> It is not fixed, because the limitation comes from the internal crypto context
> maintained by the IPP crypto library. Different versions of TDX module can
> use different versions of IPP library (as any good SW that aims to take latest and
> greatest version of its dependencies) and IPP library (as any library) does not
> provide any compatibility guarantees on its runtime data structures.
> So, the problem can show up if the old and new TDX module (prior and post
> TD preserving update) use different IPP versions and IPP happened to change
> internal data structure format in between these versions. There is nothing
> TDX module can really do in this case.
> But the situation can be avoided fully, if TD preserving update is not conducted
> during the TD build time.

Few questions:
1) How is TD build time defined in this scenario?
2) IIUC, this series doesn't add any protection of TDX module update
against ongoing TD build steps, is that supposed to be the
responsibility of userspace VMM?
    - If so, what prevents the series from building in this protection
in the kernel?

>
> Best Regards,
> Elena.
>
>