linux-kernel - Re: [PATCH v3 4/4] x86/sev: register tpm-svsm platform device

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Message-ID: <Z9gk0jg1JLZY4Fk9@kernel.org>
Date: Mon, 17 Mar 2025 15:34:10 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: Stefano Garzarella <sgarzare@...hat.com>,
	Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>, linux-integrity@...r.kernel.org,
	Dov Murik <dovmurik@...ux.ibm.com>,
	Dionna Glaze <dionnaglaze@...gle.com>, linux-coco@...ts.linux.dev,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Claudio Carvalho <cclaudio@...ux.ibm.com>,
	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH v3 4/4] x86/sev: register tpm-svsm platform device

On Fri, Mar 14, 2025 at 11:56:31AM -0500, Tom Lendacky wrote:
> On 3/11/25 04:42, Stefano Garzarella wrote:
> > SNP platform can provide a vTPM device emulated by SVSM.
> > 
> > The "tpm-svsm" device can be handled by the platform driver added
> > by the previous commit in drivers/char/tpm/tpm_svsm.c
> > 
> > The driver will call snp_svsm_vtpm_probe() to check if SVSM is
> > present and if it's support the vTPM protocol.
> > 
> > Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> > ---
> >  arch/x86/coco/sev/core.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> > index 2166bdff88b7..a2383457889e 100644
> > --- a/arch/x86/coco/sev/core.c
> > +++ b/arch/x86/coco/sev/core.c
> > @@ -2664,6 +2664,11 @@ static struct platform_device sev_guest_device = {
> >  	.id		= -1,
> >  };
> >  
> > +static struct platform_device tpm_svsm_device = {
> > +	.name		= "tpm-svsm",
> > +	.id		= -1,
> > +};
> > +
> >  static int __init snp_init_platform_device(void)
> >  {
> >  	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> > @@ -2672,6 +2677,9 @@ static int __init snp_init_platform_device(void)
> >  	if (platform_device_register(&sev_guest_device))
> >  		return -ENODEV;
> >  
> > +	if (platform_device_register(&tpm_svsm_device))
> > +		return -ENODEV;
> > +
> 
> You could avoid registering the device if an SVSM isn't present. Not sure
> if that is desirable or not.

Is there any use for the device if an SVSM isn't present? :-)

I'd judge it based on that...

> 
> Thanks,
> Tom
> 
> >  	pr_info("SNP guest platform device initialized.\n");
> >  	return 0;
> >  }
> 

BR, Jarkko