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Date:   Tue, 25 Jan 2022 14:48:51 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Brijesh Singh <brijesh.singh@amd.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
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Subject: Re: [PATCH v8 33/40] x86/compressed/64: add identity mapping for
 Confidential Computing blob
Message-ID: <Ye//w6Qm4P6HX870@zn.tnic>
References: <20211210154332.11526-1-brijesh.singh@amd.com>
 <20211210154332.11526-34-brijesh.singh@amd.com>
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In-Reply-To: <20211210154332.11526-34-brijesh.singh@amd.com>
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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.

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