linux-kernel - [PATCH] KVM: SEV: Disable SEV-SNP support on initialization failure

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Message-ID: <20250508225257.9810-1-Ashish.Kalra@amd.com>
Date: Thu, 8 May 2025 22:52:57 +0000
From: Ashish Kalra <Ashish.Kalra@....com>
To: <seanjc@...gle.com>, <pbonzini@...hat.com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<thomas.lendacky@....com>, <shuah@...nel.org>, <prsampat@....com>
CC: <pgonda@...gle.com>, <nikunj@....com>, <pankaj.gupta@....com>,
	<michael.roth@....com>, <sraithal@....com>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>, <kvm@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
	<linux-coco@...ts.linux.dev>
Subject: [PATCH] KVM: SEV: Disable SEV-SNP support on initialization failure

From: Ashish Kalra <ashish.kalra@....com>

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@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Co-developed-by: Pratik R. Sampat <prsampat@....com>
Signed-off-by: Pratik R. Sampat <prsampat@....com>
Signed-off-by: Ashish Kalra <ashish.kalra@....com>
---
 arch/x86/kvm/svm/sev.c | 43 +++++++++++++++++++++++++++++++++---------
 1 file changed, 34 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index ada53f04158c..a6abdb26f877 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2934,6 +2934,32 @@ void __init sev_set_cpu_caps(void)
 	}
 }
 
+static bool sev_is_snp_initialized(void)
+{
+	struct sev_user_data_snp_status *status;
+	struct sev_data_snp_addr buf;
+	bool initialized = false;
+	void *data;
+	int error;
+
+	data = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
+	if (!data)
+		return initialized;
+
+	buf.address = __psp_pa(data);
+	if (sev_do_cmd(SEV_CMD_SNP_PLATFORM_STATUS, &buf, &error))
+		goto out;
+
+	status = (struct sev_user_data_snp_status *)data;
+	if (status->state)
+		initialized = true;
+
+out:
+	snp_free_firmware_page(data);
+
+	return initialized;
+}
+
 void __init sev_hardware_setup(void)
 {
 	unsigned int eax, ebx, ecx, edx, sev_asid_count, sev_es_asid_count;
@@ -3038,6 +3064,14 @@ 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
+			sev_snp_supported &= sev_is_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" :
@@ -3064,15 +3098,6 @@ 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)
-- 
2.34.1