linux-kernel - Re: [PATCH v4 13/15] x86/sev: Take advantage of configfs visibility support in TSM

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Date: Wed, 1 May 2024 20:40:43 -0700
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: Tom Lendacky <thomas.lendacky@....com>, linux-kernel@...r.kernel.org, x86@...nel.org, 
	linux-coco@...ts.linux.dev, svsm-devel@...onut-svsm.dev, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Michael Roth <michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH v4 13/15] x86/sev: Take advantage of configfs visibility
 support in TSM

On Wed, May 1, 2024 at 1:15 PM Dan Williams <dan.j.williams@...el.com> wrote:
>
> Kuppuswamy Sathyanarayanan wrote:
> > On Wed, Apr 24, 2024 at 9:00 AM Tom Lendacky <thomas.lendacky@....com> wrote:
> > >
> > > The TSM attestation report support provides multiple configfs attribute
> > > types (both for standard and binary attributes) to allow for additional
> > > attributes to be displayed for SNP as compared to TDX. With the ability
> > > to hide attributes via configfs, consoldate the multiple attribute groups
> > > into a single standard attribute group and a single binary attribute
> > > group. Modify the TDX support to hide the attributes that were previously
> > > "hidden" as a result of registering the selective attribute groups.
> > >
> > > Co-developed-by: Dan Williams <dan.j.williams@...el.com>
> > > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> > > Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> [..]
> > > + */
> > > +enum tsm_attr_index {
> > > +       TSM_REPORT_GENERATION,
> >
> > Do we need an index for the generation attribute ? Since it is a core
> > function, we can allow it by default.
>
> That is up to the is_visible() callback to decide the declaration of
> which index corresponds to which attribute is just static information.
>
> >
> > > +       TSM_REPORT_PROVIDER,
> >
> > Same as above.
>
> These numbers need to match the array indices of tsm_report_attrs.
>
> Your suggestion makes the declaration of tsm_report_attrs more
> difficult:
>
>  static struct configfs_attribute *tsm_report_attrs[] = {
>     [TSM_REPORT_GENERATION] = &tsm_report_attr_generation,
>     [TSM_REPORT_PROVIDER] = &tsm_report_attr_provider,
>     [TSM_REPORT_PRIVLEVEL] = &tsm_report_attr_privlevel,
>     [TSM_REPORT_PRIVLEVEL_FLOOR] = &tsm_report_attr_privlevel_floor,
>     NULL,
>  };
>
> ...because then the definition of TSM_REPORT_PRIVLEVEL would need to
> know how many attributes precede it in the array. So, defining it this
> way makes it more robust against future changes that want to
> add/delete/reorder attributes in the array.

Got it. Makes sense. It is simpler to do it this way. I am just
worried that the vendor driver might mistakenly disable some core
attributes like inblob, outblob, provider and generation.