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

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Message-ID: <u3hnfqimgnavrhy4wxa63zorvbjomj5ptoqrn4aqnr5wlnjtxs@xyy6d4merpvy>
Date: Wed, 5 Mar 2025 10:07:03 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
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 Tue, Mar 04, 2025 at 07:27:30PM +0200, Jarkko Sakkinen wrote:
>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.

Yeah, I think we are now aligned, I will try to fix in the next version!

Thanks,
Stefano