In case when vcpus are explicitly enabled/disabled in a non-consecutive
order within a libvirt xml, it results in a drc index mismatch during
vcpu hotplug later because the existing logic uses vcpu id to derive the
corresponding drc index which is not correct. Use env->core_index to
derive a vcpu's drc index as appropriate to fix this issue.

For ex, for the given libvirt xml config:
  <vcpus>
    <vcpu id='0' enabled='yes' hotpluggable='no'/>
    <vcpu id='1' enabled='yes' hotpluggable='yes'/>
    <vcpu id='2' enabled='no' hotpluggable='yes'/>
    <vcpu id='3' enabled='yes' hotpluggable='yes'/>
    <vcpu id='4' enabled='no' hotpluggable='yes'/>
    <vcpu id='5' enabled='yes' hotpluggable='yes'/>
    <vcpu id='6' enabled='no' hotpluggable='yes'/>
    <vcpu id='7' enabled='no' hotpluggable='yes'/>
  </vcpus>

We see below error on guest console with "virsh setvcpus <domain> 5" :

pseries-hotplug-cpu: CPU with drc index 10000002 already exists

This patch fixes the issue by using correct drc index for explicitly
enabled vcpus during init.

Reported-by: Anushree Mathur <anushree.mathur@linux.vnet.ibm.com>
Tested-by: Anushree Mathur <anushree.mathur@linux.vnet.ibm.com>
Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
(cherry picked from commit e8185fdc63e1db1efba695aae568fae8a075a815)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 370d7c35d3..0307953fe5 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -758,7 +758,7 @@ static void spapr_dt_cpu(CPUState *cs, void *fdt, int offset,
     uint32_t radix_AP_encodings[PPC_PAGE_SIZES_MAX_SZ];
     int i;
 
-    drc = spapr_drc_by_id(TYPE_SPAPR_DRC_CPU, index);
+    drc = spapr_drc_by_id(TYPE_SPAPR_DRC_CPU, env->core_index);
     if (drc) {
         drc_index = spapr_drc_index(drc);
         _FDT((fdt_setprop_cell(fdt, offset, "ibm,my-drc-index", drc_index)));
-- 
2.39.5