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

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Message-ID: <YMw4UZn6AujpPSZO@zn.tnic>
Date:   Fri, 18 Jun 2021 08:08:17 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     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>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        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 Wed, Jun 02, 2021 at 09:04:14AM -0500, Brijesh Singh wrote:
> While launching the encrypted guests, the hypervisor may need to provide
> some additional information that will used during the guest boot. In the
> case of AMD SEV-SNP the information includes the address of the secrets
> and CPUID pages. The secrets page contains information such as a VM to
> PSP communication key and CPUID page contain PSP filtered CPUID values.
> 
> When booting under the EFI based BIOS, the EFI configuration table
> contains an entry for the confidential computing blob. In order to support
> booting encrypted guests on non EFI VM, the hypervisor to pass these
> additional information to the kernel with different method.
> 
> For this purpose expand the struct setup_header to hold the physical
> address of the confidential computing blob location. Being zero means it
> isn't passed.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  Documentation/x86/boot.rst            | 27 +++++++++++++++++++++++++++
>  arch/x86/boot/header.S                |  7 ++++++-
>  arch/x86/include/uapi/asm/bootparam.h |  1 +
>  3 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst
> index fc844913dece..9b32805617bb 100644
> --- a/Documentation/x86/boot.rst
> +++ b/Documentation/x86/boot.rst
> @@ -75,6 +75,8 @@ Protocol 2.14	BURNT BY INCORRECT COMMIT
>  		DO NOT USE!!! ASSUME SAME AS 2.13.
>  
>  Protocol 2.15	(Kernel 5.5) Added the kernel_info and kernel_info.setup_type_max.
> +
> +Protocol 2.16	(Kernel 5.14) Added the confidential computing blob address
>  =============	============================================================
>  
>  .. note::
> @@ -226,6 +228,7 @@ Offset/Size	Proto		Name			Meaning
>  0260/4		2.10+		init_size		Linear memory required during initialization
>  0264/4		2.11+		handover_offset		Offset of handover entry point
>  0268/4		2.15+		kernel_info_offset	Offset of the kernel_info
> +026C/4		2.16+		cc_blob_address	        Physical address of the confidential computing blob

Why is this a separate thing instead of being passed as setup_data?

-- 
Regards/Gruss,
    Boris.

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