KVM: x86: Implement MSR_CORE_THREAD_COUNT MSR

The MSR_CORE_THREAD_COUNT MSR describes CPU package topology, such as number
of threads and cores for a given package. This is information that QEMU has
readily available and can provide through the new user space MSR deflection
interface.

This patch propagates the existing hvf logic from patch 027ac0c
("target/i386/hvf: add rdmsr 35H MSR_CORE_THREAD_COUNT") to KVM.

Signed-off-by: Alexander Graf <agraf@csgraf.de>
Message-Id: <20221004225643.65036-4-agraf@csgraf.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/kvm/kvm.c

@@ -2401,6 +2401,17 @@ static int kvm_get_supported_msrs(KVMState *s)
     return ret;
 }
 
+static bool kvm_rdmsr_core_thread_count(X86CPU *cpu, uint32_t msr,
+                                        uint64_t *val)
+{
+    CPUState *cs = CPU(cpu);
+
+    *val = cs->nr_threads * cs->nr_cores; /* thread count, bits 15..0 */
+    *val |= ((uint32_t)cs->nr_cores << 16); /* core count, bits 31..16 */
+
+    return true;
+}
+
 static Notifier smram_machine_done;
 static KVMMemoryListener smram_listener;
 static AddressSpace smram_address_space;
@@ -2613,13 +2624,23 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
             }
     }
     if (kvm_vm_check_extension(s, KVM_CAP_X86_USER_SPACE_MSR)) {
+        bool r;
+
         ret = kvm_vm_enable_cap(s, KVM_CAP_X86_USER_SPACE_MSR, 0,
                                 KVM_MSR_EXIT_REASON_FILTER);
         if (ret) {
             error_report("Could not enable user space MSRs: %s",
                          strerror(-ret));
             exit(1);
         }
+
+        r = kvm_filter_msr(s, MSR_CORE_THREAD_COUNT,
+                           kvm_rdmsr_core_thread_count, NULL);
+        if (!r) {
+            error_report("Could not install MSR_CORE_THREAD_COUNT handler: %s",
+                         strerror(-ret));
+            exit(1);
+        }
     }
 
     return 0;