linux-kernel - Re: [PATCH v9 32/43] x86/boot: Add a pointer to Confidential Computing blob in bootparams

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Date:   Sat, 5 Feb 2022 14:07:45 +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>,
        brijesh.ksingh@...il.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v9 32/43] x86/boot: Add a pointer to Confidential
 Computing blob in bootparams

On Fri, Jan 28, 2022 at 11:17:53AM -0600, Brijesh Singh wrote:
> From: Michael Roth <michael.roth@....com>
> 
> The previously defined Confidential Computing blob is provided to the
> kernel via a setup_data structure or EFI config table entry. Currently
> these are both checked for by boot/compressed kernel to access the
> CPUID table address within it for use with SEV-SNP CPUID enforcement.
> 
> To also enable SEV-SNP CPUID enforcement for the run-time kernel,
> similar early access to the CPUID table is needed early on while it's
> still using the identity-mapped page table set up by boot/compressed,
> where global pointers need to be accessed via fixup_pointer().
> 
> This isn't much of an issue for accessing setup_data, and the EFI
> config table helper code currently used in boot/compressed *could* be
> used in this case as well since they both rely on identity-mapping.
> However, it has some reliance on EFI helpers/string constants that
> would need to be accessed via fixup_pointer(), and fixing it up while
> making it shareable between boot/compressed and run-time kernel is
> fragile and introduces a good bit of uglyness.
> 
> Instead, add a boot_params->cc_blob_address pointer that the
> boot/compressed kernel can initialize so that the run-time kernel can
> access the CC blob from there instead of re-scanning the EFI config
> table.
> 
> Signed-off-by: Michael Roth <michael.roth@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/include/asm/bootparam_utils.h | 1 +
>  arch/x86/include/uapi/asm/bootparam.h  | 3 ++-
>  2 files changed, 3 insertions(+), 1 deletion(-)

Another review comment ignored:

https://lore.kernel.org/r/YeWyCtr11rL7dxpT@zn.tnic

/me ignores this patch too.

-- 
Regards/Gruss,
    Boris.

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