target-i386: Implement CPUID[0xB] (Extended Topology Enumeration)

I looked at a dozen Intel CPU that have this CPUID and all of them
always had Core offset as 1 (a wasted bit when hyperthreading is
disabled) and Package offset at least 4 (wasted bits at <= 4 cores).

QEMU uses more compact IDs and it doesn't make much sense to change it
now. I keep the SMT and Core sub-leaves even if there is just one
thread/core; it makes the code simpler and there should be no harm.

Backports commit 5232d00a041c8f3628b3532ef35d703a1f0dac19 from qemu

qemu/target-i386/cpu.c

@@ -35,6 +35,7 @@
 #include "hw/hw.h"
 
 #include "sysemu/sysemu.h"
+#include "topology.h"
 #include "hw/cpu/icc_bus.h"
 #ifndef CONFIG_USER_ONLY
 #include "exec/address-spaces.h"
@@ -2423,6 +2424,36 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         *ecx = 0;
         *edx = 0;
         break;
+    case 0xB:
+        /* Extended Topology Enumeration Leaf */
+        if (!cpu->enable_cpuid_0xb) {
+                *eax = *ebx = *ecx = *edx = 0;
+                break;
+        }
+
+        *ecx = count & 0xff;
+        *edx = cpu->apic_id;
+
+        switch (count) {
+        case 0:
+            *eax = apicid_core_offset(smp_cores, smp_threads);
+            *ebx = smp_threads;
+            *ecx |= CPUID_TOPOLOGY_LEVEL_SMT;
+            break;
+        case 1:
+            *eax = apicid_pkg_offset(smp_cores, smp_threads);
+            *ebx = smp_cores * smp_threads;
+            *ecx |= CPUID_TOPOLOGY_LEVEL_CORE;
+            break;
+        default:
+            *eax = 0;
+            *ebx = 0;
+            *ecx |= CPUID_TOPOLOGY_LEVEL_INVALID;
+        }
+
+        assert(!(*eax & ~0x1f));
+        *ebx &= 0xffff; /* The count doesn't need to be reliable. */
+        break;
     case 0xD: {
         uint64_t ena_mask;
         int i;

qemu/target-i386/cpu.h

@@ -635,6 +635,11 @@ typedef uint32_t FeatureWordArray[FEATURE_WORDS];
 #define CPUID_MWAIT_IBE     (1U << 1) /* Interrupts can exit capability */
 #define CPUID_MWAIT_EMX     (1U << 0) /* enumeration supported */
 
+/* CPUID[0xB].ECX level types */
+#define CPUID_TOPOLOGY_LEVEL_INVALID  (0U << 8)
+#define CPUID_TOPOLOGY_LEVEL_SMT      (1U << 8)
+#define CPUID_TOPOLOGY_LEVEL_CORE     (2U << 8)
+
 #ifndef HYPERV_SPINLOCK_NEVER_RETRY
 #define HYPERV_SPINLOCK_NEVER_RETRY             0xFFFFFFFF
 #endif
@@ -1160,6 +1165,9 @@ typedef struct X86CPU {
      */
     bool enable_pmu;
 
+    /* Compatibility bits for old machine types: */
+    bool enable_cpuid_0xb;
+
     /* in order to simplify APIC support, we leave this pointer to the
        user */
     struct DeviceState *apic_state;