8365673: Incorrect number of cores are reported on Ryzen CPU

Reviewed-by: dholmes, kvn

Author: YaSuenag

src/hotspot/cpu/x86/vm_version_x86.cpp

@@ -3148,7 +3148,10 @@ uint VM_Version::cores_per_cpu() {
       result = (_cpuid_info.dcp_cpuid4_eax.bits.cores_per_cpu + 1);
     }
   } else if (is_amd_family()) {
-    result = (_cpuid_info.ext_cpuid8_ecx.bits.cores_per_cpu + 1);
+    result = _cpuid_info.ext_cpuid8_ecx.bits.threads_per_cpu + 1;
+    if (cpu_family() >= 0x17) { // Zen or later
+      result /= _cpuid_info.ext_cpuid1E_ebx.bits.threads_per_core + 1;
+    }
   } else if (is_zx()) {
     bool supports_topology = supports_processor_topology();
     if (supports_topology) {

src/hotspot/cpu/x86/vm_version_x86.hpp

@@ -199,8 +199,8 @@ class VM_Version : public Abstract_VM_Version {
   union ExtCpuid8Ecx {
     uint32_t value;
     struct {
-      uint32_t cores_per_cpu : 8,
-                             : 24;
+      uint32_t threads_per_cpu : 8,
+                               : 24;
     } bits;
   };