linux-kernel - Re: [PATCH Part1 RFC v3 20/22] x86/boot: Add Confidential Computing address to setup

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Message-ID: <YNnSBl5asXjXIvfy@zn.tnic>
Date:   Mon, 28 Jun 2021 15:43:34 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Michael Roth <michael.roth@....com>
Cc:     Brijesh Singh <brijesh.singh@....com>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>, tony.luck@...el.com,
        npmccallum@...hat.com
Subject: Re: [PATCH Part1 RFC v3 20/22] x86/boot: Add Confidential Computing
 address to setup_header

On Fri, Jun 25, 2021 at 01:14:17PM -0500, Michael Roth wrote:
> So non-EFI case would rely purely on the setup_data entry for both (though
> we could still use boot_params->cc_blob_address to avoid the need to scan
> setup_data list in proper kernel as well, but scanning it early on doesn't
> have the same issues as with EFI config table so it's not really
> necessary there).

Yeah, sure, we can simply always use boot_params->cc_blob_address just
like acpi_rsdp_addr and always put the CC blob address there.

> I opted to give setup_data precedence over EFI, since if a bootloader goes
> the extra mile of packaging up a setup_data argument instead of just leaving
> it to firmware/EFI config table, it might be out of some extra need.  For
> example, if we do have a shared definition for both SEV and TDX, maybe the
> bootloader needs to synthesize multiple EFI table entries, and a unified
> setup_data will be easier for the kernel to consume than replicating that same
> work, and maybe over time the fallback can be deprecated. And containers will
> more than likely prefer setup_data approach, which might drive future changes
> that aren't in lockstep with EFI definitions as well.

Yah, that makes perfect sense. And you/Brijesh should put the gist of
that in a comment over the code so that people are aware. The less we
rely on firmware, the better.

> Brijesh can correct me if I'm wrong, but I believe that's the intent, and the
> setup_data approach definitely seems workable for that aspect.

Oki doki, I think we're all on the same page then. :-)

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette