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

Dave Hansen
2021-12-10T19:53:02Z

On 12/10/21 7:43 AM, 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);
> + }

The casting here is pretty ugly. Also, isn't ->cpuid_phys already a
u64? Whats the idea behind casting it?

I also have a sneaking suspicion that a single "unsigned long cc_blob"
could remove virtually all the casting. Does this work?

unsigned long cc_blob = boot_params->cc_blob_addres;
struct cc_blob_sev_info *cc_info;

add_identity_map(cc_blob, cc_blob + sizeof(*cc_info));

cc_info = (struct cc_blob_sev_info *)cc_blob;
add_identity_map(cc_info->cpuid_phys,
cc_info->cpuid_phys + cc_info->cpuid_len);