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

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Message-ID: <cfoz65txflem7xlvqupn5ltiaad3svcwum5m2kmechzss6pnjy@fwmaj2e35ohr>
Date: Thu, 23 Jan 2025 13:29:23 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
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 01:49:34PM +0200, Jarkko Sakkinen wrote:
>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.

Yes, I completely understand your point and I admit that the cover
letter and the commits description were not very informative, I will
fix them putting more context.

>>
>> 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 see it completely!

>I neither don't want you to do useless and unproductive
>work.

Thanks for that,
Stefano