[PATCH v10 09/45] x86/mm: Extend cc_attr to include AMD SEV-SNP

[Brijesh Singh]

The CC_ATTR_GUEST_SEV_SNP can be used by the guest to query whether the
SNP (Secure Nested Paging) feature is active.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/include/asm/msr-index.h | 2 ++
 arch/x86/kernel/cc_platform.c    | 2 ++
 arch/x86/mm/mem_encrypt.c        | 4 ++++
 include/linux/cc_platform.h      | 8 ++++++++
 4 files changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 3faf0f97edb1..0b3b4dcf55a7 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -481,8 +481,10 @@
 #define MSR_AMD64_SEV			0xc0010131
 #define MSR_AMD64_SEV_ENABLED_BIT	0
 #define MSR_AMD64_SEV_ES_ENABLED_BIT	1
+#define MSR_AMD64_SEV_SNP_ENABLED_BIT	2
 #define MSR_AMD64_SEV_ENABLED		BIT_ULL(MSR_AMD64_SEV_ENABLED_BIT)
 #define MSR_AMD64_SEV_ES_ENABLED	BIT_ULL(MSR_AMD64_SEV_ES_ENABLED_BIT)
+#define MSR_AMD64_SEV_SNP_ENABLED	BIT_ULL(MSR_AMD64_SEV_SNP_ENABLED_BIT)
 
 #define MSR_AMD64_VIRT_SPEC_CTRL	0xc001011f
 
diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c
index 6a6ffcd978f6..b9d1361d112b 100644
--- a/arch/x86/kernel/cc_platform.c
+++ b/arch/x86/kernel/cc_platform.c
@@ -59,6 +59,8 @@ static bool amd_cc_platform_has(enum cc_attr attr)
 		return (sev_status & MSR_AMD64_SEV_ENABLED) &&
 			!(sev_status & MSR_AMD64_SEV_ES_ENABLED);
 
+	case CC_ATTR_GUEST_SEV_SNP:
+		return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
 	default:
 		return false;
 	}
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 50d209939c66..f85868c031c6 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -62,6 +62,10 @@ static void print_mem_encrypt_feature_info(void)
 	if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
 		pr_cont(" SEV-ES");
 
+	/* Secure Nested Paging */
+	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		pr_cont(" SEV-SNP");
+
 	pr_cont("\n");
 }
 
diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
index efd8205282da..d08dd65b5c43 100644
--- a/include/linux/cc_platform.h
+++ b/include/linux/cc_platform.h
@@ -72,6 +72,14 @@ enum cc_attr {
 	 * Examples include TDX guest & SEV.
 	 */
 	CC_ATTR_GUEST_UNROLL_STRING_IO,
+
+	/**
+	 * @CC_ATTR_SEV_SNP: Guest SNP is active.
+	 *
+	 * The platform/OS is running as a guest/virtual machine and actively
+	 * using AMD SEV-SNP features.
+	 */
+	CC_ATTR_GUEST_SEV_SNP,
 };
 
 #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
-- 
2.25.1