target/i386: Add support for MCDT_NO in CPUID enumeration

CPUID.(EAX=7,ECX=2):EDX[bit 5] enumerates MCDT_NO. Processors enumerate
this bit as 1 do not exhibit MXCSR Configuration Dependent Timing (MCDT)
behavior and do not need to be mitigated to avoid data-dependent behavior
for certain instructions.

Since MCDT_NO is in a new sub-leaf, add a new CPUID feature word
FEAT_7_2_EDX. Also update cpuid_level_func7 by FEAT_7_2_EDX.

Signed-off-by: Tao Su <tao1.su@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-ID: <20230706054949.66556-3-tao1.su@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/cpu.c

@@ -739,6 +739,7 @@ void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
 #define TCG_7_1_EAX_FEATURES (CPUID_7_1_EAX_FZRM | CPUID_7_1_EAX_FSRS | \
           CPUID_7_1_EAX_FSRC)
 #define TCG_7_1_EDX_FEATURES 0
+#define TCG_7_2_EDX_FEATURES 0
 #define TCG_APM_FEATURES 0
 #define TCG_6_EAX_FEATURES CPUID_6_EAX_ARAT
 #define TCG_XSAVE_FEATURES (CPUID_XSAVE_XSAVEOPT | CPUID_XSAVE_XGETBV1)
@@ -993,6 +994,25 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
         },
         .tcg_features = TCG_7_1_EDX_FEATURES,
     },
+    [FEAT_7_2_EDX] = {
+        .type = CPUID_FEATURE_WORD,
+        .feat_names = {
+            NULL, NULL, NULL, NULL,
+            NULL, "mcdt-no", 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 = 7,
+            .needs_ecx = true, .ecx = 2,
+            .reg = R_EDX,
+        },
+        .tcg_features = TCG_7_2_EDX_FEATURES,
+    },
     [FEAT_8000_0007_EDX] = {
         .type = CPUID_FEATURE_WORD,
         .feat_names = {
@@ -6017,6 +6037,11 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
             *edx = env->features[FEAT_7_1_EDX];
             *ebx = 0;
             *ecx = 0;
+        } else if (count == 2) {
+            *edx = env->features[FEAT_7_2_EDX];
+            *eax = 0;
+            *ebx = 0;
+            *ecx = 0;
         } else {
             *eax = 0;
             *ebx = 0;
@@ -6881,6 +6906,7 @@ void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
         x86_cpu_adjust_feat_level(cpu, FEAT_7_0_ECX);
         x86_cpu_adjust_feat_level(cpu, FEAT_7_1_EAX);
         x86_cpu_adjust_feat_level(cpu, FEAT_7_1_EDX);
+        x86_cpu_adjust_feat_level(cpu, FEAT_7_2_EDX);
         x86_cpu_adjust_feat_level(cpu, FEAT_8000_0001_EDX);
         x86_cpu_adjust_feat_level(cpu, FEAT_8000_0001_ECX);
         x86_cpu_adjust_feat_level(cpu, FEAT_8000_0007_EDX);

target/i386/cpu.h

@@ -628,6 +628,7 @@ typedef enum FeatureWord {
     FEAT_XSAVE_XSS_LO,     /* CPUID[EAX=0xd,ECX=1].ECX */
     FEAT_XSAVE_XSS_HI,     /* CPUID[EAX=0xd,ECX=1].EDX */
     FEAT_7_1_EDX,       /* CPUID[EAX=7,ECX=1].EDX */
+    FEAT_7_2_EDX,       /* CPUID[EAX=7,ECX=2].EDX */
     FEATURE_WORDS,
 } FeatureWord;
 
@@ -932,6 +933,9 @@ uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
 /* PREFETCHIT0/1 Instructions */
 #define CPUID_7_1_EDX_PREFETCHITI       (1U << 14)
 
+/* Do not exhibit MXCSR Configuration Dependent Timing (MCDT) behavior */
+#define CPUID_7_2_EDX_MCDT_NO           (1U << 5)
+
 /* XFD Extend Feature Disabled */
 #define CPUID_D_1_EAX_XFD               (1U << 4)