i386: Introduce ARAT CPU feature

From: Jan Kiszka <[email protected]>

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 Jan Kiszka <[email protected]>

---

Changes in v5:
- rebased over master

 include/hw/i386/pc.h |  7 ++++++-
 target-i386/cpu.c    | 33 ++++++++++++++++++++++++++++++++-
 target-i386/cpu.h    |  3 +++
 target-i386/kvm.c    |  2 ++
 4 files changed, 43 insertions(+), 2 deletions(-)

include/hw/i386/pc.h +6 -1

index bec6de1..3b0b30f 100644
@@ -294,7 +294,12 @@ 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 +32 -1

index 99ad551..b5b9fc2 100644
@@ -284,6 +284,17 @@ 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)

@@ -339,6 +350,7 @@ 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 {

@@ -408,6 +420,11 @@ 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 {

@@ -1001,6 +1018,8 @@ 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)",
     },

@@ -1030,6 +1049,8 @@ 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)",
     },

@@ -1062,6 +1083,8 @@ 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)",
     },

@@ -1096,6 +1119,8 @@ 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)",
     },    {

@@ -1130,6 +1155,8 @@ 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)",
     },

@@ -1166,6 +1193,8 @@ 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)",
     },

@@ -1202,6 +1231,8 @@ 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)",
     },

@@ -2358,7 +2389,7 @@ 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 +3 -0

index 26182bd..074a9c9 100644
@@ -412,6 +412,7 @@ 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;
 

@@ -577,6 +578,8 @@ 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 +0 -0

index ca2da84..d7bd205 100644

From: Jan Kiszka <[email protected]>

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 Jan Kiszka <[email protected]>

---

Changes in v5:
- rebased over master

 include/hw/i386/pc.h |  7 ++++++-
 target-i386/cpu.c    | 33 ++++++++++++++++++++++++++++++++-
 target-i386/cpu.h    |  3 +++
 target-i386/kvm.c    |  2 ++
 4 files changed, 43 insertions(+), 2 deletions(-)

include/hw/i386/pc.h +6 -1

index bec6de1..3b0b30f 100644
@@ -294,7 +294,12 @@ 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 +32 -1

index 99ad551..b5b9fc2 100644
@@ -284,6 +284,17 @@ 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)

@@ -339,6 +350,7 @@ 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 {

@@ -408,6 +420,11 @@ 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 {

@@ -1001,6 +1018,8 @@ 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)",
     },

@@ -1030,6 +1049,8 @@ 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)",
     },

@@ -1062,6 +1083,8 @@ 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)",
     },

@@ -1096,6 +1119,8 @@ 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)",
     },    {

@@ -1130,6 +1155,8 @@ 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)",
     },

@@ -1166,6 +1193,8 @@ 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)",
     },

@@ -1202,6 +1231,8 @@ 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)",
     },

@@ -2358,7 +2389,7 @@ 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 +3 -0

index 26182bd..074a9c9 100644
@@ -412,6 +412,7 @@ 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;
 

@@ -577,6 +578,8 @@ 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 +2 -0

index ca2da84..d7bd205 100644
@@ -233,6 +233,8 @@ 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:

Signature · 1 line

2.1.4

From: Jan Kiszka <[email protected]>

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 Jan Kiszka <[email protected]>

Quoted 9 lines · Jan Kiszka

From: Jan Kiszka <[email protected]>

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.

Quoted 1 line

Signed-off-by Jan Kiszka <[email protected]>

The code looks good now, but: what are the real consequences of enabling/disabling the flag? What exactly guests use it for?

Isn't this going to make guests have additional expectations about the APIC timer that may be broken when live-migrating or pausing the VM?

Quoted 11 lines · Eduardo Habkost

Quoted 10 lines · Jan Kiszka

From: Jan Kiszka <[email protected]>

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 Jan Kiszka <[email protected]>

Quoted 5 lines

The code looks good now, but: what are the real consequences of enabling/disabling the flag? What exactly guests use it for?

Isn't this going to make guests have additional expectations about the APIC timer that may be broken when live-migrating or pausing the VM?

ARAT only refers to stopping of the timer in certain power states (which we do not even emulate IIRC). In that case, the OS is under risk of sleeping forever, thus need to look for a different wakeup source.

Live-migration or VM pausing are external effects on all timers of the guest, not only the APIC. However, none of them cause a wakeup miss - provided the host decides to resume the guest eventually.

Jan

Quoted 15 lines · Jan Kiszka

Quoted 14 lines · Eduardo Habkost

Quoted 10 lines · Jan Kiszka

From: Jan Kiszka <[email protected]>

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 Jan Kiszka <[email protected]>

The code looks good now, but: what are the real consequences of enabling/disabling the flag? What exactly guests use it for?

Quoted 5 lines

Quoted 2 lines

Isn't this going to make guests have additional expectations about the APIC timer that may be broken when live-migrating or pausing the VM?

ARAT only refers to stopping of the timer in certain power states (which we do not even emulate IIRC). In that case, the OS is under risk of sleeping forever, thus need to look for a different wakeup source.

HPET will always be the default broadcast event device I think.

From: Jan Kiszka <[email protected]>

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 Jan Kiszka <[email protected]>