i386: Introduce ARAT CPU feature

ARAT signals that the APIC timer does not stop in power saving states.
As our APICs are emulated, it's fine to expose this feature to guests,
at least when asking for KVM host features or with CPU types that
include the flag. The exact model number that introduced the feature is
not known, but reports can be found that it's at least available since
Sandy Bridge.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

include/hw/i386/pc.h

@@ -293,7 +293,12 @@ int e820_get_num_entries(void);
 bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 
 #define PC_COMPAT_2_3 \
-        HW_COMPAT_2_3
+        HW_COMPAT_2_3 \
+        {\
+            .driver   = TYPE_X86_CPU,\
+            .property = "arat",\
+            .value    = "off",\
+        },
 
 #define PC_COMPAT_2_2 \
         PC_COMPAT_2_3 \

target-i386/cpu.c

@@ -286,6 +286,17 @@ static const char *cpuid_xsave_feature_name[] = {
     NULL, NULL, NULL, NULL,
 };
 
+static const char *cpuid_6_feature_name[] = {
+    NULL, NULL, "arat", 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,
+};
+
 #define I486_FEATURES (CPUID_FP87 | CPUID_VME | CPUID_PSE)
 #define PENTIUM_FEATURES (I486_FEATURES | CPUID_DE | CPUID_TSC | \
           CPUID_MSR | CPUID_MCE | CPUID_CX8 | CPUID_MMX | CPUID_APIC)
@@ -341,6 +352,7 @@ static const char *cpuid_xsave_feature_name[] = {
           CPUID_7_0_EBX_ERMS, CPUID_7_0_EBX_INVPCID, CPUID_7_0_EBX_RTM,
           CPUID_7_0_EBX_RDSEED */
 #define TCG_APM_FEATURES 0
+#define TCG_6_EAX_FEATURES CPUID_6_EAX_ARAT
 
 
 typedef struct FeatureWordInfo {
@@ -410,6 +422,11 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
         .cpuid_reg = R_EAX,
         .tcg_features = 0,
     },
+    [FEAT_6_EAX] = {
+        .feat_names = cpuid_6_feature_name,
+        .cpuid_eax = 6, .cpuid_reg = R_EAX,
+        .tcg_features = TCG_6_EAX_FEATURES,
+    },
 };
 
 typedef struct X86RegisterInfo32 {
@@ -1003,6 +1020,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT2_LM | CPUID_EXT2_SYSCALL | CPUID_EXT2_NX,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_LAHF_LM,
+        .features[FEAT_6_EAX] =
+            CPUID_6_EAX_ARAT,
         .xlevel = 0x8000000A,
         .model_id = "Westmere E56xx/L56xx/X56xx (Nehalem-C)",
     },
@@ -1032,6 +1051,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT3_LAHF_LM,
         .features[FEAT_XSAVE] =
             CPUID_XSAVE_XSAVEOPT,
+        .features[FEAT_6_EAX] =
+            CPUID_6_EAX_ARAT,
         .xlevel = 0x8000000A,
         .model_id = "Intel Xeon E312xx (Sandy Bridge)",
     },
@@ -1064,6 +1085,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT3_LAHF_LM,
         .features[FEAT_XSAVE] =
             CPUID_XSAVE_XSAVEOPT,
+        .features[FEAT_6_EAX] =
+            CPUID_6_EAX_ARAT,
         .xlevel = 0x8000000A,
         .model_id = "Intel Xeon E3-12xx v2 (Ivy Bridge)",
     },
@@ -1098,6 +1121,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_7_0_EBX_BMI2 | CPUID_7_0_EBX_ERMS | CPUID_7_0_EBX_INVPCID,
         .features[FEAT_XSAVE] =
             CPUID_XSAVE_XSAVEOPT,
+        .features[FEAT_6_EAX] =
+            CPUID_6_EAX_ARAT,
         .xlevel = 0x8000000A,
         .model_id = "Intel Core Processor (Haswell, no TSX)",
     },    {
@@ -1132,6 +1157,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_7_0_EBX_RTM,
         .features[FEAT_XSAVE] =
             CPUID_XSAVE_XSAVEOPT,
+        .features[FEAT_6_EAX] =
+            CPUID_6_EAX_ARAT,
         .xlevel = 0x8000000A,
         .model_id = "Intel Core Processor (Haswell)",
     },
@@ -1168,6 +1195,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_7_0_EBX_SMAP,
         .features[FEAT_XSAVE] =
             CPUID_XSAVE_XSAVEOPT,
+        .features[FEAT_6_EAX] =
+            CPUID_6_EAX_ARAT,
         .xlevel = 0x8000000A,
         .model_id = "Intel Core Processor (Broadwell, no TSX)",
     },
@@ -1204,6 +1233,8 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_7_0_EBX_SMAP,
         .features[FEAT_XSAVE] =
             CPUID_XSAVE_XSAVEOPT,
+        .features[FEAT_6_EAX] =
+            CPUID_6_EAX_ARAT,
         .xlevel = 0x8000000A,
         .model_id = "Intel Core Processor (Broadwell)",
     },
@@ -2359,7 +2390,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         break;
     case 6:
         /* Thermal and Power Leaf */
-        *eax = 0;
+        *eax = env->features[FEAT_6_EAX];
         *ebx = 0;
         *ecx = 0;
         *edx = 0;

target-i386/cpu.h

@@ -415,6 +415,7 @@ typedef enum FeatureWord {
     FEAT_KVM,           /* CPUID[4000_0001].EAX (KVM_CPUID_FEATURES) */
     FEAT_SVM,           /* CPUID[8000_000A].EDX */
     FEAT_XSAVE,         /* CPUID[EAX=0xd,ECX=1].EAX */
+    FEAT_6_EAX,         /* CPUID[6].EAX */
     FEATURE_WORDS,
 } FeatureWord;
 
@@ -580,6 +581,8 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS];
 #define CPUID_XSAVE_XGETBV1    (1U << 2)
 #define CPUID_XSAVE_XSAVES     (1U << 3)
 
+#define CPUID_6_EAX_ARAT       (1U << 2)
+
 /* CPUID[0x80000007].EDX flags: */
 #define CPUID_APM_INVTSC       (1U << 8)
 

target-i386/kvm.c

@@ -238,6 +238,8 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
         if (!kvm_irqchip_in_kernel()) {
             ret &= ~CPUID_EXT_X2APIC;
         }
+    } else if (function == 6 && reg == R_EAX) {
+        ret |= CPUID_6_EAX_ARAT; /* safe to allow because of emulated APIC */
     } else if (function == 0x80000001 && reg == R_EDX) {
         /* On Intel, kvm returns cpuid according to the Intel spec,
          * so add missing bits according to the AMD spec: