i386: Add SGX CPUID leaf FEAT_SGX_12_0_EBX

CPUID leaf 12_0_EBX is an Intel-defined feature bits leaf enumerating
the platform's SGX extended capabilities.  Currently there is a single
capabilitiy:

   - EXINFO: record information about #PFs and #GPs in the enclave's SSA

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20210719112136.57018-9-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/cpu.c

@@ -655,6 +655,7 @@ void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
           CPUID_XSAVE_XSAVEC, CPUID_XSAVE_XSAVES */
 #define TCG_14_0_ECX_FEATURES 0
 #define TCG_SGX_12_0_EAX_FEATURES 0
+#define TCG_SGX_12_0_EBX_FEATURES 0
 
 FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
     [FEAT_1_EDX] = {
@@ -1202,6 +1203,26 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
         },
         .tcg_features = TCG_SGX_12_0_EAX_FEATURES,
     },
+
+    [FEAT_SGX_12_0_EBX] = {
+        .type = CPUID_FEATURE_WORD,
+        .feat_names = {
+            "sgx-exinfo" , NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+            NULL, NULL, NULL, NULL,
+        },
+        .cpuid = {
+            .eax = 0x12,
+            .needs_ecx = true, .ecx = 0,
+            .reg = R_EBX,
+        },
+        .tcg_features = TCG_SGX_12_0_EBX_FEATURES,
+    },
 };
 
 typedef struct FeatureMask {

target/i386/cpu.h

@@ -579,6 +579,7 @@ typedef enum FeatureWord {
     FEAT_VMX_VMFUNC,
     FEAT_14_0_ECX,
     FEAT_SGX_12_0_EAX,  /* CPUID[EAX=0x12,ECX=0].EAX (SGX) */
+    FEAT_SGX_12_0_EBX,  /* CPUID[EAX=0x12,ECX=0].EBX (SGX MISCSELECT[31:0]) */
     FEATURE_WORDS,
 } FeatureWord;