linux-kernel - Re: [PATCH v8 33/40] x86/compressed/64: add identity mapping for Confidential Computing blob

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Date:   Tue, 25 Jan 2022 14:48:51 +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 33/40] x86/compressed/64: add identity mapping for
 Confidential Computing blob

On Fri, Dec 10, 2021 at 09:43:25AM -0600, Brijesh Singh wrote:
> +static void sev_prep_identity_maps(void)
> +{
> +	/*
> +	 * The ConfidentialComputing blob is used very early in uncompressed
> +	 * kernel to find the in-memory cpuid table to handle cpuid
> +	 * instructions. Make sure an identity-mapping exists so it can be
> +	 * accessed after switchover.
> +	 */
> +	if (sev_snp_enabled()) {
> +		struct cc_blob_sev_info *cc_info =
> +			(void *)(unsigned long)boot_params->cc_blob_address;
> +
> +		add_identity_map((unsigned long)cc_info,
> +				 (unsigned long)cc_info + sizeof(*cc_info));
> +		add_identity_map((unsigned long)cc_info->cpuid_phys,
> +				 (unsigned long)cc_info->cpuid_phys + cc_info->cpuid_len);
> +	}
> +
> +	sev_verify_cbit(top_level_pgt);
> +}
> +

Also, that function can just as well live in compressed/sev.c and
you can export add_identity_map() instead.

That latter function calls kernel_ident_mapping_init() which is
already exported. add_identity_map() doesn't do anything special
and it is limited to the decompressor kernel so nothing stands in
the way of exporting it in a pre-patch and renaming it there to
kernel_add_identity_map() or so...

Thx.

-- 
Regards/Gruss,
    Boris.

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