apic: Drop APICCommonState.idx and use APIC ID as index in local_apics[]

local_apics[] is sized to contain all APIC ID supported in xAPIC mode,
so use APIC ID as index in it instead of constantly increasing counter idx.

Fixes error "apic initialization failed" when a CPU hotplugged and
unplugged more times than there are free slots in local_apics[].

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

hw/intc/apic.c

@@ -421,7 +421,7 @@ static int apic_find_dest(uint8_t dest)
     int i;
 
     if (apic && apic->id == dest)
-        return dest;  /* shortcut in case apic->id == apic->idx */
+        return dest;  /* shortcut in case apic->id == local_apics[dest]->id */
 
     for (i = 0; i < MAX_APICS; i++) {
         apic = local_apics[i];
@@ -504,14 +504,14 @@ static void apic_deliver(DeviceState *dev, uint8_t dest, uint8_t dest_mode,
         break;
     case 1:
         memset(deliver_bitmask, 0x00, sizeof(deliver_bitmask));
-        apic_set_bit(deliver_bitmask, s->idx);
+        apic_set_bit(deliver_bitmask, s->id);
         break;
     case 2:
         memset(deliver_bitmask, 0xff, sizeof(deliver_bitmask));
         break;
     case 3:
         memset(deliver_bitmask, 0xff, sizeof(deliver_bitmask));
-        apic_reset_bit(deliver_bitmask, s->idx);
+        apic_reset_bit(deliver_bitmask, s->id);
         break;
     }
 
@@ -871,20 +871,18 @@ static const MemoryRegionOps apic_io_ops = {
 static void apic_realize(DeviceState *dev, Error **errp)
 {
     APICCommonState *s = APIC_COMMON(dev);
-    static int apic_no;
 
-    if (apic_no >= MAX_APICS) {
-        error_setg(errp, "%s initialization failed.",
-                   object_get_typename(OBJECT(dev)));
+    if (s->id >= MAX_APICS) {
+        error_setg(errp, "%s initialization failed. APIC ID %d is invalid",
+                   object_get_typename(OBJECT(dev)), s->id);
         return;
     }
-    s->idx = apic_no++;
 
     memory_region_init_io(&s->io_memory, OBJECT(s), &apic_io_ops, s, "apic-msi",
                           APIC_SPACE_SIZE);
 
     s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, apic_timer, s);
-    local_apics[s->idx] = s;
+    local_apics[s->id] = s;
 
     msi_nonbroken = true;
 }

include/hw/i386/apic_internal.h

@@ -174,7 +174,6 @@ struct APICCommonState {
     uint32_t initial_count;
     int64_t initial_count_load_time;
     int64_t next_time;
-    int idx; /* not actually common, used only by 'apic' derived class */
     QEMUTimer *timer;
     int64_t timer_expiry;
     int sipi_vector;