linux-kernel - Re: [PATCH 3/3] x86/sev: add a SVSM vTPM platform device

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Message-Id: <D79FHC9OB5WS.CCNDGUTDNG31@kernel.org>
Date: Thu, 23 Jan 2025 13:49:34 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "Stefano Garzarella"
 <sgarzare@...hat.com>
Cc: "Dionna Amalie Glaze" <dionnaglaze@...gle.com>, "Jarkko Sakkinen"
 <jarkko.sakkinen@....fi>, "Jason Gunthorpe" <jgg@...pe.ca>, "James
 Bottomley" <james.bottomley@...senpartnership.com>,
 <linux-coco@...ts.linux.dev>, "Borislav Petkov" <bp@...en8.de>, "Dave
 Hansen" <dave.hansen@...ux.intel.com>, "Peter Huewe" <peterhuewe@....de>,
 "H. Peter Anvin" <hpa@...or.com>, <linux-integrity@...r.kernel.org>,
 <x86@...nel.org>, "Joerg Roedel" <jroedel@...e.de>,
 <linux-kernel@...r.kernel.org>, "Ingo Molnar" <mingo@...hat.com>, "Thomas
 Gleixner" <tglx@...utronix.de>, "Claudio Carvalho"
 <cclaudio@...ux.ibm.com>, "Dov Murik" <dovmurik@...ux.ibm.com>, "Tom
 Lendacky" <thomas.lendacky@....com>
Subject: Re: [PATCH 3/3] x86/sev: add a SVSM vTPM platform device

On Thu Jan 23, 2025 at 1:46 PM EET, Jarkko Sakkinen wrote:
> On Thu Jan 23, 2025 at 12:09 PM EET, Stefano Garzarella wrote:
> > On Thu, Jan 23, 2025 at 11:50:40AM +0200, Jarkko Sakkinen wrote:
> > >On Wed Jan 22, 2025 at 11:29 PM EET, Dionna Amalie Glaze wrote:
> > >> I can appreciate this viewpoint. It even surfaced Microsoft's fTPM
> > >> paper to me, which solves some interesting problems we need to solve
> > >> in SVSM too. So thanks for that.
> > >>
> > >> Just to clarify, you're not asking for SVSM to implement the TIS-MMIO
> > >> interface instead, but rather to use the fTPM stack, which could make
> > >> SVSM calls a TEE device operation?
> > >
> > >I don't really know what I'm asking because this is barely even a
> > >PoC, and I state it like this knowingly.
> > >
> > >You should make the argument, and the case for the solution. Then
> > >it is my turn to comment on that scheme.
> >
> > I'll check if I can use fTPM, in the meantime I had started to simplify
> > this series, avoiding the double stack and exposing some APIs from SEV
> > to probe the vTPM and to send the commands. The final driver in
> > drivers/char/tpm would be quite simple.
> >
> > But I'll try to see if reusing fTPM is a feasible way, I like the idea.
> >
> > >
> > >That said, I would not give high odds for acceptance of a duplicate
> > >TPM stack succeeding.
> >
> > Got it ;-)
> >
> > Thanks to everyone for the helpful feedbacks!
> >
> > I've been a bit messy these days and I'm in FOSDEM next week, so I hope
> > not to take too long for the v2.
>
> Yeah, OK one thing that I want to say.
>
> Nail the story. What is it about what is the problem what is the
> motivation to solve it etc. If you have all that properly written
> up then it is easier to forgive not that well nailed code and
> give reasonable arguments.
>
> And don't rush, I have all the time in the world ;-)

Here the point is that if I don't fully understand the context
(starting explaining the obvious like what is SVSM) I might 
give some ridiculously wrong advice.

Then people come back to me and start blaming me on saying
opposite arguments. I hope you see where I'm standing here.
I neither don't want you to do useless and unproductive
work.

BR, Jarkko