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

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Message-ID: <CAGxU2F4YQy-otsGtGiUHDiL7PGXic2_HzWL_+GHkn+Hs_ScGpQ@mail.gmail.com>
Date: Tue, 14 Jan 2025 11:42:34 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jarkko Sakkinen <jarkko.sakkinen@....fi>
Cc: 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>, Jarkko Sakkinen <jarkko@...nel.org>, 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

Hi Jarkko,

On Thu, 19 Dec 2024 at 17:07, Stefano Garzarella <sgarzare@...hat.com> wrote:
>
> On Thu, Dec 19, 2024 at 05:40:58PM +0200, Jarkko Sakkinen wrote:
> >On Thu Dec 19, 2024 at 5:35 PM EET, Stefano Garzarella wrote:
> >> So to use them directly in sev, we would have to move these definitions
> >> into include/linux/tpm.h or some other file in inlcude/. Is this
> >> acceptable for TPM maintainers?
> >
> >There's only me.
> >
> >I don't know.
> >
> >What you want to put to include/linux/tpm.h anyway?
>
> At least tpmm_chip_alloc(), tpm2_probe(), and tpm_chip_register()
>
> >I have not followed this discussion.
>
> Let me try to summarize what we are doing: We are writing a small TPM
> driver to support AMD SEV-SNP SVSM. Basically SVSM defines some sort of
> hypercalls, which the guest OS can call to talk to the emulated vTPM.
>
> In the current version of this series, based on James' RFC, we have an
> intermediate module (tpm_platform) and then another small driver
> (platform_device) in arch/x86/coco/sev/core.c that registers the
> callback to use.
>
> To avoid the intermediate driver (Jason correct me if I misunderstood),
> we want to register the `tpm_chip` with its `tpm_class_ops` directly in
> arch/x86/coco/sev/core.c where it's easy to use "SVSM calls" (i.e.
> svsm_perform_call_protocol()).
>
> And here I have this problem, so I was proposing to expose these APIs.
> BTW, we do have an alternative though that I proposed in the previous
> email that might avoid this.

Any thought on this?

Thanks,
Stefano