linux-kernel - Re: [RFC PATCH v2 5/6] tpm: add SNP SVSM vTPM driver

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Message-ID: <Z8c4Avw2y7k4JODe@kernel.org>
Date: Tue, 4 Mar 2025 19:27:30 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Claudio Carvalho <cclaudio@...ux.ibm.com>,
	Peter Huewe <peterhuewe@....de>, x86@...nel.org,
	Dov Murik <dovmurik@...ux.ibm.com>, linux-coco@...ts.linux.dev,
	Dionna Glaze <dionnaglaze@...gle.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
	Jason Gunthorpe <jgg@...pe.ca>, linux-integrity@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH v2 5/6] tpm: add SNP SVSM vTPM driver

On Mon, Mar 03, 2025 at 05:46:16PM +0100, Stefano Garzarella wrote:
> On Sat, Mar 01, 2025 at 03:51:46AM +0200, Jarkko Sakkinen wrote:
> > On Fri, Feb 28, 2025 at 06:07:19PM +0100, Stefano Garzarella wrote:
> > > Add driver for the vTPM defined by the AMD SVSM spec [1].
> > > 
> > > The specification defines a protocol that a SEV-SNP guest OS can use to
> > > discover and talk to a vTPM emulated by the Secure VM Service Module (SVSM)
> > > in the guest context, but at a more privileged level (VMPL0).
> > > 
> > > The new tpm-svsm platform driver uses two functions exposed by x86/sev
> > > to verify that the device is actually emulated by the platform and to
> > > send commands and receive responses.
> > > 
> > > The vTPM is emulated through the TCG reference implementation, so this
> > > driver leverages tpm_tcgsim.h to fill commands and parse responses.
> > 
> > Why? Please don't.
> 
> You mean it's better not to have the external header and have all the
> functions here to prepare commands and parse responses?
> 
> As I mentioned, I did this because there may be other future drivers that
> could use it to talk to emulated devices in the same way, that is, through
> the TCG TPM reference implementation,

Sorry about harsh comment. I think we discussed this (MS simulator
caused confusion). Anchor this to SVSM spec and we're fine.

BR, Jarkko