Re: [PATCH v2 6/8] x86/sev: Register the guest with the SVSM APIC protocol

[Melody Wang]

Hi Ard,

On 9/15/26 12:44 AM, Ard Biesheuvel wrote:
> So please add it to the EFI stub, and code it against the boot services
> (efi_err() for error messages, efi_exit() when aborting and returning to
> the firmware, etc). Implementing this in a hybrid manner seems entirely
> unnecessary.

I moved sev_prepare() into the EFI stub, and I wrote a wrapper for 
registering Alternate Injection in the EFI stub but kept the code in 
compressed, otherwise I have to export early_is_sevsnp_guest(), 
boot_svsm_caa_pa, and svsm_call_msr_protocol() so that it builds.

How about this below:

This is in the stub:

static bool sev_prepare(void)
{
        u64 unsupported;

        unsupported = snp_get_unsupported_features(sev_get_status());
        if (unsupported) {
                efi_err("Unsupported SEV-SNP features detected: 0x%llx\n",
                        unsupported);
                return true;
        }

        register_alternate_injection();

        return false;
}

and the stub calls this function:

+void register_alternate_injection(void)
+{
+       if (early_is_sevsnp_guest() && snp_vmpl) {
+               struct svsm_call call = {};
+               int ret;
+
+               if (!(sev_get_status() & MSR_AMD64_SNP_ALTERNATE_INJ))
+                       return;
+
+               call.caa = (struct svsm_ca *)boot_svsm_caa_pa;
+               call.rax = SVSM_APIC_CALL(SVSM_APIC_CONFIG_EMULATION);
+               call.rcx = SVSM_AI_REGISTER;
+
+               ret = svsm_call_msr_protocol(&call);
+               if (ret)
+                       sev_es_terminate(SEV_TERM_SET_LINUX, 
GHCB_TERM_ALT_INJ_FAIL);
+       }
+}

which is kept in sev.c to avoid cross-dependencies.

I can send it as patches too if it is easier to review this way.

--
Thanks,
Melody