diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
index ac0f900ebc47..1632d40e1f54 100644
--- a/arch/x86/boot/string.c
+++ b/arch/x86/boot/string.c
@@ -32,8 +32,15 @@
 int memcmp(const void *s1, const void *s2, size_t len)
 {
 	bool diff;
-	asm("repe cmpsb"
-	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
+
+	/*
+	 * Make sure ZF is properly set in the len==0 case because in it,
+	 * RCX==0 and the REPE; CMPSB won't get executed.
+	 */
+	asm volatile("test %3, %3\n\t"
+		     "repe cmpsb"
+		     : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len)
+		     : : "cc", "memory");
 	return diff;
 }
 
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 487ac147e11f..d61df70d6875 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -515,11 +515,13 @@ static void bsp_init_amd(struct cpuinfo_x86 *c)
 		case 0x00 ... 0x2f:
 		case 0x40 ... 0x4f:
 		case 0x60 ... 0x7f:
+		case 0xd0 ... 0xd7:
 			setup_force_cpu_cap(X86_FEATURE_ZEN5);
 			break;
 		case 0x50 ... 0x5f:
 		case 0x80 ... 0xaf:
-		case 0xc0 ... 0xef:
+		case 0xc0 ... 0xcf:
+		case 0xd8 ... 0xef:
 			setup_force_cpu_cap(X86_FEATURE_ZEN6);
 			break;
 		default: