linux-kernel - Re: [PATCH v8 30/40] x86/boot: add a pointer to Confidential Computing blob in bootparams

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Date:   Mon, 17 Jan 2022 19:14:34 +0100
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,
        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>,
        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>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v8 30/40] x86/boot: add a pointer to Confidential
 Computing blob in bootparams

On Fri, Dec 10, 2021 at 09:43:22AM -0600, Brijesh Singh wrote:
> diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
> index 1ac5acca72ce..bea5cdcdf532 100644
> --- a/arch/x86/include/uapi/asm/bootparam.h
> +++ b/arch/x86/include/uapi/asm/bootparam.h
> @@ -188,7 +188,8 @@ struct boot_params {
>  	__u32 ext_ramdisk_image;			/* 0x0c0 */
>  	__u32 ext_ramdisk_size;				/* 0x0c4 */
>  	__u32 ext_cmd_line_ptr;				/* 0x0c8 */
> -	__u8  _pad4[116];				/* 0x0cc */
> +	__u8  _pad4[112];				/* 0x0cc */
> +	__u32 cc_blob_address;				/* 0x13c */
>  	struct edid_info edid_info;			/* 0x140 */
>  	struct efi_info efi_info;			/* 0x1c0 */
>  	__u32 alt_mem_k;				/* 0x1e0 */

Yes, you said that this is a boot/compressed stage -> kernel proper info
pass field but let's document it anyway, please, and say what it is,
just like:

	1E4/004         ALL     scratch                 Scratch field for the kernel setup code

is documented, for example.

And now that I look at it, acpi_rsdp_addr isn't documented either so if
you wanna add it too, while you're at it, that would be nice.

Thx.

-- 
Regards/Gruss,
    Boris.

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