KVM: SEV: Disable SEV-SNP support on initialization failure

JIRA: https://issues.redhat.com/browse/RHEL-120168

commit 179a842
Author: Ashish Kalra <ashish.kalra@amd.com>
Date:   Mon May 12 22:16:34 2025 +0000

    KVM: SEV: Disable SEV-SNP support on initialization failure

    During platform init, SNP initialization may fail for several reasons,
    such as firmware command failures and incompatible versions. However,
    the KVM capability may continue to advertise support for it.

    The platform may have SNP enabled but if SNP_INIT fails then SNP is
    not supported by KVM.

    During KVM module initialization query the SNP platform status to obtain
    the SNP initialization state and use it as an additional condition to
    determine support for SEV-SNP.

    Co-developed-by: Sean Christopherson <seanjc@google.com>
    Signed-off-by: Sean Christopherson <seanjc@google.com>
    Co-developed-by: Pratik R. Sampat <prsampat@amd.com>
    Signed-off-by: Pratik R. Sampat <prsampat@amd.com>
    Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
    Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
    Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>
    Reviewed-by: Pavan Kumar Paluri <papaluri@amd.com>
    Message-ID: <20250512221634.12045-1-Ashish.Kalra@amd.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>

Author: Maxim Levitsky

arch/x86/kvm/svm/sev.c

@@ -2883,6 +2883,33 @@ void __init sev_set_cpu_caps(void)
 	}
 }
 
+static bool is_sev_snp_initialized(void)
+{
+	struct sev_user_data_snp_status *status;
+	struct sev_data_snp_addr buf;
+	bool initialized = false;
+	int ret, error = 0;
+
+	status = snp_alloc_firmware_page(GFP_KERNEL | __GFP_ZERO);
+	if (!status)
+		return false;
+
+	buf.address = __psp_pa(status);
+	ret = sev_do_cmd(SEV_CMD_SNP_PLATFORM_STATUS, &buf, &error);
+	if (ret) {
+		pr_err("SEV: SNP_PLATFORM_STATUS failed ret=%d, fw_error=%d (%#x)\n",
+		       ret, error, error);
+		goto out;
+	}
+
+	initialized = !!status->state;
+
+out:
+	snp_free_firmware_page(status);
+
+	return initialized;
+}
+
 void __init sev_hardware_setup(void)
 {
 	unsigned int eax, ebx, ecx, edx, sev_asid_count, sev_es_asid_count;
@@ -2977,6 +3004,14 @@ void __init sev_hardware_setup(void)
 	sev_snp_supported = sev_snp_enabled && cc_platform_has(CC_ATTR_HOST_SEV_SNP);
 
 out:
+	if (sev_enabled) {
+		init_args.probe = true;
+		if (sev_platform_init(&init_args))
+			sev_supported = sev_es_supported = sev_snp_supported = false;
+		else if (sev_snp_supported)
+			sev_snp_supported = is_sev_snp_initialized();
+	}
+
 	if (boot_cpu_has(X86_FEATURE_SEV))
 		pr_info("SEV %s (ASIDs %u - %u)\n",
 			sev_supported ? min_sev_asid <= max_sev_asid ? "enabled" :
@@ -3003,15 +3038,6 @@ void __init sev_hardware_setup(void)
 	sev_supported_vmsa_features = 0;
 	if (sev_es_debug_swap_enabled)
 		sev_supported_vmsa_features |= SVM_SEV_FEAT_DEBUG_SWAP;
-
-	if (!sev_enabled)
-		return;
-
-	/*
-	 * Do both SNP and SEV initialization at KVM module load.
-	 */
-	init_args.probe = true;
-	sev_platform_init(&init_args);
 }
 
 void sev_hardware_unsetup(void)