Re: [PATCH] x86/CPU/AMD, mm: Extend with mem_encrypt=sme option

[Brijesh Singh <brijesh.singh@xxxxxxx>]

>
> So I want to be able to disable SEV and the whole code that comes with
> it in the *host*.

We can add a new variable 'sme_only'. By default this variable should be set
to false. When mem_encrypt=sme is passed then set it to true and
based on sme_only state early_detect_mem_encrypt() can clear X86_FEATURE_SEV
flag.

Here are the changes on top of your patch. I did a quick test in both host and
guest OS and it seems to be working okay. In host OS mem_encrypt=sme disabled
the SEV but in guest its still don't care. I will do more test later...

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 175310f00202..73a6fb3b14a1 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -19,7 +19,7 @@
 
 #include <asm/bootparam.h>
 
-extern bool sev_enabled;
+extern bool sme_only;
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index d0669f3966a6..a09b02959874 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -33,7 +33,7 @@ static bool cpu_has_amd_erratum(struct cpuinfo_x86 *cpu, const int *erratum);
  */
 static u32 nodes_per_socket = 1;
 
-bool sev_enabled __section(.data) = false;
+bool sme_only __section(.data) = false;
 
 static inline int rdmsrl_amd_safe(unsigned msr, unsigned long long *p)
 {
@@ -591,7 +591,7 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
 		if (IS_ENABLED(CONFIG_X86_32))
 			goto clear_all;
 
-		if (!sev_enabled)
+		if (sme_only)
 			goto clear_sev;
 
 		rdmsrl(MSR_K7_HWCR, msr);
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 9b83bc1be7c0..a135e4497021 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -45,6 +45,7 @@ u64 sme_me_mask __section(.data) = 0;
 EXPORT_SYMBOL_GPL(sme_me_mask);
 DEFINE_STATIC_KEY_FALSE(__sev);
 EXPORT_SYMBOL_GPL(__sev);
+static bool sev_enabled __section(.data) = false;
 
 /* Buffer used for early in-place encryption by BSP, no locking needed */
 static char sme_early_buffer[PAGE_SIZE] __aligned(PAGE_SIZE);
@@ -773,7 +774,6 @@ void __init __nostackprotector sme_enable(struct boot_params *bp)
 	unsigned long feature_mask;
 	u64 me_mask, msr;
 	char buffer[16];
-	bool sme_only;
 	int ret;
 
 	/* Check for the SME/SEV support leaf */
@@ -808,6 +808,8 @@ void __init __nostackprotector sme_enable(struct boot_params *bp)
 	if (!(eax & feature_mask))
 		return;
 
+	me_mask = BIT_ULL(ebx & 0x3f);
+
 	/* For SME, check the SYSCFG MSR */
 	if (feature_mask == AMD_SME_BIT) {
 		msr = __rdmsr(MSR_K8_SYSCFG);
@@ -820,9 +822,13 @@ void __init __nostackprotector sme_enable(struct boot_params *bp)
 		msr = __rdmsr(MSR_AMD64_SEV);
 		if (!(msr & MSR_AMD64_SEV_ENABLED))
 			return;
-	}
 
-	me_mask = BIT_ULL(ebx & 0x3f);
+		if (feature_mask == AMD_SEV_BIT) {
+			sme_me_mask = me_mask;
+			sev_enabled = true;
+			return;
+		}
+	}
 
 	/*
 	 * Fixups have not been applied to phys_base yet and we're running
@@ -847,16 +853,11 @@ void __init __nostackprotector sme_enable(struct boot_params *bp)
 	} else if (!strncmp(buffer, cmd_on, sizeof(buffer))) {
 		sme_me_mask = me_mask;
 	} else if (!strncmp(buffer, cmd_sme, sizeof(buffer))) {
+		sme_me_mask = me_mask;
 		sme_only = true;
+		return;
 	}
 
 	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT))
 		sme_me_mask = me_mask;
-
-	if (sme_only)
-		return;
-
-	/* For SEV, check the SEV MSR */
-	if (feature_mask == AMD_SEV_BIT)
-		sev_enabled = true;
 }
-- 
2.9.5