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

[Jarkko Sakkinen <jarkko@kernel.org>]

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@redhat.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