[PATCH] x86/sev: Check whether SEV or SME is supported first

[Pu Wen]

The first two bits of the CPUID leaf 0x8000001F EAX indicate whether
SEV or SME is supported respectively. It's better to check whether
SEV or SME is supported before checking the SEV MSR(0xc0010131) to
see whether SEV or SME is enabled.

This also avoid the MSR reading failure on the first generation Hygon
Dhyana CPU which does not support SEV or SME.

Fixes: eab696d8e8b9 ("x86/sev: Do not require Hypervisor CPUID bit for SEV guests")
Cc: <stable@xxxxxxxxxxxxxxx> # v5.10+
Signed-off-by: Pu Wen <puwen@xxxxxxxx>
---
 arch/x86/mm/mem_encrypt_identity.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index a9639f663d25..470b20208430 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -504,10 +504,6 @@ void __init sme_enable(struct boot_params *bp)
 #define AMD_SME_BIT	BIT(0)
 #define AMD_SEV_BIT	BIT(1)
 
-	/* Check the SEV MSR whether SEV or SME is enabled */
-	sev_status   = __rdmsr(MSR_AMD64_SEV);
-	feature_mask = (sev_status & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
-
 	/*
 	 * Check for the SME/SEV feature:
 	 *   CPUID Fn8000_001F[EAX]
@@ -519,11 +515,16 @@ void __init sme_enable(struct boot_params *bp)
 	eax = 0x8000001f;
 	ecx = 0;
 	native_cpuid(&eax, &ebx, &ecx, &edx);
-	if (!(eax & feature_mask))
+	/* Check whether SEV or SME is supported */
+	if (!(eax & (AMD_SEV_BIT | AMD_SME_BIT)))
 		return;
 
 	me_mask = 1UL << (ebx & 0x3f);
 
+	/* Check the SEV MSR whether SEV or SME is enabled */
+	sev_status   = __rdmsr(MSR_AMD64_SEV);
+	feature_mask = (sev_status & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
+
 	/* Check if memory encryption is enabled */
 	if (feature_mask == AMD_SME_BIT) {
 		/*
-- 
2.23.0