[Qemu-devel] [PATCH v3] target-i386: implement CPUID[0xB] (Extended Topology Enumeration)

["Radim Krčmář" <rkrcmar@redhat.com>]

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.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 This patch depends on Igor's "pc: add 2.7 machine".

 v2:
 * assert *eax instead of silently masking [Eduardo]
 * backward compatibility through CPU property [Eduardo]

 v3: use count instead of *ecx to access leaves, hardware does

 include/hw/i386/pc.h  |  7 ++++++-
 target-i386/cpu-qom.h |  3 +++
 target-i386/cpu.c     | 32 ++++++++++++++++++++++++++++++++
 target-i386/cpu.h     |  5 +++++
 4 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index a91e8e734f07..e294fa945d30 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -361,7 +361,12 @@ int e820_get_num_entries(void);
 bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 
 #define PC_COMPAT_2_6 \
-    HW_COMPAT_2_6
+    HW_COMPAT_2_6 \
+    {\
+        .driver   = TYPE_X86_CPU,\
+        .property = "cpuid-0xb",\
+        .value    = "off",\
+    },
 
 #define PC_COMPAT_2_5 \
     PC_COMPAT_2_6 \
diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h
index cb750176c0c0..b84963d42463 100644
--- a/target-i386/cpu-qom.h
+++ b/target-i386/cpu-qom.h
@@ -115,6 +115,9 @@ 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;
diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index d0b5b691563c..a17ef191c270 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -35,6 +35,7 @@
 #include "sysemu/arch_init.h"
 
 #include "hw/hw.h"
+#include "hw/i386/topology.h"
 #if defined(CONFIG_KVM)
 #include <linux/kvm_para.h>
 #endif
@@ -2460,6 +2461,36 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
             *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: {
         KVMState *s = cs->kvm_state;
         uint64_t ena_mask;
@@ -3221,6 +3252,7 @@ static Property x86_cpu_properties[] = {
     DEFINE_PROP_UINT32("xlevel", X86CPU, env.cpuid_xlevel, 0),
     DEFINE_PROP_UINT32("xlevel2", X86CPU, env.cpuid_xlevel2, 0),
     DEFINE_PROP_STRING("hv-vendor-id", X86CPU, hyperv_vendor_id),
+    DEFINE_PROP_BOOL("cpuid-0xb", X86CPU, enable_cpuid_0xb, true),
     DEFINE_PROP_END_OF_LIST()
 };
 
diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index 732eb6d7ec79..b460c2debc1c 100644
--- a/target-i386/cpu.h
+++ b/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
-- 
2.8.2