[Qemu-devel] [PATCH RFC] x86: BFloat16 feature enabling on Cooper Lake

[Jing Liu]

Intel CooperLake cpu adds AVX512_BF16 instruction, defining as
CPUID.(EAX=7,EXC=1):EAX[bit 05].

The release spec link as follows,
https://software.intel.com/sites/default/files/managed/c5/15/\
architecture-instruction-set-extensions-programming-reference.pdf

Signed-off-by: Jing Liu <address@hidden>
---
 target/i386/cpu.c | 46 +++++++++++++++++++++++++++++++++++++++-------
 target/i386/cpu.h |  3 +++
 target/i386/kvm.c |  3 ++-
 3 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index c1ab86d..249f7f9 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -664,6 +664,9 @@ static CPUCacheInfo legacy_l3_cache = {
 #define L2_ITLB_4K_ASSOC       4
 #define L2_ITLB_4K_ENTRIES   512
 
+/* CPUID Leaf 0x07 constants: */
+#define INTEL_LEAF_7_MAX_SUBLEAF     0x1
+
 /* CPUID Leaf 0x14 constants: */
 #define INTEL_PT_MAX_SUBLEAF     0x1
 /*
@@ -767,6 +770,7 @@ static void x86_cpu_vendor_words2str(char *dst, uint32_t 
vendor1,
           /* CPUID_7_0_ECX_OSPKE is dynamic */ \
           CPUID_7_0_ECX_LA57)
 #define TCG_7_0_EDX_FEATURES 0
+#define TCG_7_1_EAX_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)
@@ -1092,6 +1096,25 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] 
= {
         },
         .tcg_features = TCG_7_0_EDX_FEATURES,
     },
+    [FEAT_7_1_EAX] = {
+        .type = CPUID_FEATURE_WORD,
+        .feat_names = {
+            NULL, NULL, NULL, NULL,
+            NULL, "avx512-bf16", 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 = 1,
+            .reg = R_EAX,
+        },
+        .tcg_features = TCG_7_1_EAX_FEATURES,
+    },
     [FEAT_8000_0007_EDX] = {
         .type = CPUID_FEATURE_WORD,
         .feat_names = {
@@ -4343,19 +4366,28 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
uint32_t count,
         break;
     case 7:
         /* Structured Extended Feature Flags Enumeration Leaf */
-        if (count == 0) {
-            *eax = 0; /* Maximum ECX value for sub-leaves */
+        *eax = 0;
+        *ebx = 0;
+        *ecx = 0;
+        *edx = 0;
+
+        switch (count) {
+        case 0:
+            if (env->features[FEAT_7_1_EAX] & CPUID_7_1_EAX_AVX512_BF16) {
+                *eax = INTEL_LEAF_7_MAX_SUBLEAF; /* Maximum ECX value for 
sub-leaves */
+            }
             *ebx = env->features[FEAT_7_0_EBX]; /* Feature flags */
             *ecx = env->features[FEAT_7_0_ECX]; /* Feature flags */
             if ((*ecx & CPUID_7_0_ECX_PKU) && env->cr[4] & CR4_PKE_MASK) {
                 *ecx |= CPUID_7_0_ECX_OSPKE;
             }
             *edx = env->features[FEAT_7_0_EDX]; /* Feature flags */
-        } else {
-            *eax = 0;
-            *ebx = 0;
-            *ecx = 0;
-            *edx = 0;
+            break;
+        case 1:
+            *eax = env->features[FEAT_7_1_EAX];
+            break;
+        default:
+            break;
         }
         break;
     case 9:
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index bd06523..40594a1 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -488,6 +488,7 @@ typedef enum FeatureWord {
     FEAT_7_0_EBX,       /* CPUID[EAX=7,ECX=0].EBX */
     FEAT_7_0_ECX,       /* CPUID[EAX=7,ECX=0].ECX */
     FEAT_7_0_EDX,       /* CPUID[EAX=7,ECX=0].EDX */
+    FEAT_7_1_EAX,       /* CPUID[EAX=7,ECX=1].EAX */
     FEAT_8000_0001_EDX, /* CPUID[8000_0001].EDX */
     FEAT_8000_0001_ECX, /* CPUID[8000_0001].ECX */
     FEAT_8000_0007_EDX, /* CPUID[8000_0007].EDX */
@@ -699,6 +700,8 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS];
 #define CPUID_7_0_EDX_ARCH_CAPABILITIES (1U << 29)  /*Arch Capabilities*/
 #define CPUID_7_0_EDX_SPEC_CTRL_SSBD  (1U << 31) /* Speculative Store Bypass 
Disable */
 
+#define CPUID_7_1_EAX_AVX512_BF16 (1U << 5) /* AVX512 BFloat16 Instruction */
+
 #define CPUID_8000_0008_EBX_WBNOINVD  (1U << 9)  /* Write back and
                                                                              
do not invalidate cache */
 #define CPUID_8000_0008_EBX_IBPB    (1U << 12) /* Indirect Branch Prediction 
Barrier */
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 3b29ce5..977aaa5 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -1110,6 +1110,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
                 c = &cpuid_data.entries[cpuid_i++];
             }
             break;
+        case 0x7:
         case 0x14: {
             uint32_t times;
 
@@ -1122,7 +1123,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
             for (j = 1; j <= times; ++j) {
                 if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
                     fprintf(stderr, "cpuid_data is full, no space for "
-                                "cpuid(eax:0x14,ecx:0x%x)\n", j);
+                                "cpuid(eax:0x%x,ecx:0x%x)\n", i, j);
                     abort();
                 }
                 c = &cpuid_data.entries[cpuid_i++];
-- 
1.8.3.1