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

[Borislav Petkov]

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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