[PATCH Part1 RFC v4 04/36] x86/mm: Add sev_feature_enabled() helper

[Brijesh Singh <brijesh.singh@xxxxxxx>]

The sev_feature_enabled() helper 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/mem_encrypt.h |  8 ++++++++
 arch/x86/include/asm/msr-index.h   |  2 ++
 arch/x86/mm/mem_encrypt.c          | 14 ++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 8cc2fd308f65..fb857f2e72cb 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -16,6 +16,12 @@
 
 #include <asm/bootparam.h>
 
+enum sev_feature_type {
+	SEV,
+	SEV_ES,
+	SEV_SNP
+};
+
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 
 extern u64 sme_me_mask;
@@ -54,6 +60,7 @@ void __init sev_es_init_vc_handling(void);
 bool sme_active(void);
 bool sev_active(void);
 bool sev_es_active(void);
+bool sev_feature_enabled(unsigned int feature_type);
 
 #define __bss_decrypted __section(".bss..decrypted")
 
@@ -87,6 +94,7 @@ static inline int __init
 early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0; }
 
 static inline void mem_encrypt_free_decrypted_mem(void) { }
+static bool sev_feature_enabled(unsigned int feature_type) { return false; }
 
 #define __bss_decrypted
 
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index a7c413432b33..37589da0282e 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/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index ff08dc463634..63e7799a9a86 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -389,6 +389,16 @@ bool noinstr sev_es_active(void)
 	return sev_status & MSR_AMD64_SEV_ES_ENABLED;
 }
 
+bool sev_feature_enabled(unsigned int type)
+{
+	switch (type) {
+	case SEV: return sev_status & MSR_AMD64_SEV_ENABLED;
+	case SEV_ES: return sev_status & MSR_AMD64_SEV_ES_ENABLED;
+	case SEV_SNP: return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
+	default: return false;
+	}
+}
+
 /* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
 bool force_dma_unencrypted(struct device *dev)
 {
@@ -461,6 +471,10 @@ static void print_mem_encrypt_feature_info(void)
 	if (sev_es_active())
 		pr_cont(" SEV-ES");
 
+	/* Secure Nested Paging */
+	if (sev_feature_enabled(SEV_SNP))
+		pr_cont(" SEV-SNP");
+
 	pr_cont("\n");
 }
 
-- 
2.17.1