machine: introduce MachineClass.possible_cpu_arch_ids() hook

on x86 currently range 0..max_cpus is used to generate
architecture-dependent CPU ID (APIC Id) for each present
and possible CPUs. However architecture-dependent CPU IDs
list could be sparse and code that needs to enumerate
all IDs (ACPI) ended up doing guess work enumerating all
possible and impossible IDs up to
  apic_id_limit = x86_cpu_apic_id_from_index(max_cpus).

That leads to creation of MADT entries and Processor
objects in ACPI tables for not possible CPUs.
Fix it by allowing board specify a concrete list of
CPU IDs accourding its own rules (which for x86 depends
on topology). So that code that needs this list could
request it from board instead of trying to guess
what IDs are correct on its own.

This interface will also allow to help making AML
part of CPU hotplug target independent so it could
be reused for ARM target.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>

hw/i386/pc.c

@@ -1131,11 +1131,18 @@ void pc_cpus_init(PCMachineState *pcms)
         exit(1);
     }
 
-    for (i = 0; i < smp_cpus; i++) {
+    pcms->possible_cpus = g_malloc0(sizeof(CPUArchIdList) +
+                                    sizeof(CPUArchId) * max_cpus);
+    for (i = 0; i < max_cpus; i++) {
+        pcms->possible_cpus->cpus[i].arch_id = x86_cpu_apic_id_from_index(i);
+        pcms->possible_cpus->len++;
+        if (i < smp_cpus) {
             cpu = pc_new_cpu(machine->cpu_model, x86_cpu_apic_id_from_index(i),
                              &error_fatal);
+            pcms->possible_cpus->cpus[i].cpu = CPU(cpu);
             object_unref(OBJECT(cpu));
         }
+    }
 
     /* tell smbios about cpuid version and features */
     smbios_set_cpuid(cpu->env.cpuid_version, cpu->env.features[FEAT_1_EDX]);
@@ -1657,9 +1664,19 @@ static void pc_dimm_unplug(HotplugHandler *hotplug_dev,
     error_propagate(errp, local_err);
 }
 
+static int pc_apic_cmp(const void *a, const void *b)
+{
+   CPUArchId *apic_a = (CPUArchId *)a;
+   CPUArchId *apic_b = (CPUArchId *)b;
+
+   return apic_a->arch_id - apic_b->arch_id;
+}
+
 static void pc_cpu_plug(HotplugHandler *hotplug_dev,
                         DeviceState *dev, Error **errp)
 {
+    CPUClass *cc = CPU_GET_CLASS(dev);
+    CPUArchId apic_id, *found_cpu;
     HotplugHandlerClass *hhc;
     Error *local_err = NULL;
     PCMachineState *pcms = PC_MACHINE(hotplug_dev);
@@ -1682,6 +1699,13 @@ static void pc_cpu_plug(HotplugHandler *hotplug_dev,
 
     /* increment the number of CPUs */
     rtc_set_memory(pcms->rtc, 0x5f, rtc_get_memory(pcms->rtc, 0x5f) + 1);
+
+    apic_id.arch_id = cc->get_arch_id(CPU(dev));
+    found_cpu = bsearch(&apic_id, pcms->possible_cpus->cpus,
+        pcms->possible_cpus->len, sizeof(*pcms->possible_cpus->cpus),
+        pc_apic_cmp);
+    assert(found_cpu);
+    found_cpu->cpu = CPU(dev);
 out:
     error_propagate(errp, local_err);
 }
@@ -1924,6 +1948,17 @@ static unsigned pc_cpu_index_to_socket_id(unsigned cpu_index)
     return topo.pkg_id;
 }
 
+static CPUArchIdList *pc_possible_cpu_arch_ids(MachineState *machine)
+{
+    PCMachineState *pcms = PC_MACHINE(machine);
+    int len = sizeof(CPUArchIdList) +
+              sizeof(CPUArchId) * (pcms->possible_cpus->len);
+    CPUArchIdList *list = g_malloc(len);
+
+    memcpy(list, pcms->possible_cpus, len);
+    return list;
+}
+
 static void pc_machine_class_init(ObjectClass *oc, void *data)
 {
     MachineClass *mc = MACHINE_CLASS(oc);
@@ -1946,6 +1981,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     pcmc->save_tsc_khz = true;
     mc->get_hotplug_handler = pc_get_hotpug_handler;
     mc->cpu_index_to_socket_id = pc_cpu_index_to_socket_id;
+    mc->possible_cpu_arch_ids = pc_possible_cpu_arch_ids;
     mc->default_boot_order = "cad";
     mc->hot_add_cpu = pc_hot_add_cpu;
     mc->max_cpus = 255;

include/hw/boards.h

@@ -8,6 +8,7 @@
 #include "sysemu/accel.h"
 #include "hw/qdev.h"
 #include "qom/object.h"
+#include "qom/cpu.h"
 
 void memory_region_allocate_system_memory(MemoryRegion *mr, Object *owner,
                                           const char *name,
@@ -41,6 +42,26 @@ int machine_phandle_start(MachineState *machine);
 bool machine_dump_guest_core(MachineState *machine);
 bool machine_mem_merge(MachineState *machine);
 
+/**
+ * CPUArchId:
+ * @arch_id - architecture-dependent CPU ID of present or possible CPU
+ * @cpu - pointer to corresponding CPU object if it's present on NULL otherwise
+ */
+typedef struct {
+    uint64_t arch_id;
+    struct CPUState *cpu;
+} CPUArchId;
+
+/**
+ * CPUArchIdList:
+ * @len - number of @CPUArchId items in @cpus array
+ * @cpus - array of present or possible CPUs for current machine configuration
+ */
+typedef struct {
+    int len;
+    CPUArchId cpus[0];
+} CPUArchIdList;
+
 /**
  * MachineClass:
  * @get_hotplug_handler: this function is called during bus-less
@@ -57,6 +78,10 @@ bool machine_mem_merge(MachineState *machine);
  *    Set only by old machines because they need to keep
  *    compatibility on code that exposed QEMU_VERSION to guests in
  *    the past (and now use qemu_hw_version()).
+ * @possible_cpu_arch_ids:
+ *    Returns an array of @CPUArchId architecture-dependent CPU IDs
+ *    which includes CPU IDs for present and possible to hotplug CPUs.
+ *    Caller is responsible for freeing returned list.
  */
 struct MachineClass {
     /*< private >*/
@@ -98,6 +123,7 @@ struct MachineClass {
     HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
                                            DeviceState *dev);
     unsigned (*cpu_index_to_socket_id)(unsigned cpu_index);
+    CPUArchIdList *(*possible_cpu_arch_ids)(MachineState *machine);
 };
 
 /**

include/hw/i386/pc.h

@@ -67,6 +67,7 @@ struct PCMachineState {
     /* CPU and apic information: */
     bool apic_xrupt_override;
     unsigned apic_id_limit;
+    CPUArchIdList *possible_cpus;
 
     /* NUMA information: */
     uint64_t numa_nodes;