[Qemu-devel] [PATCH 4/5] spapr: consolidate the VCPU id numbering logic in a single place

[Greg Kurz]

Several places in the code need to calculate a VCPU id:

    (cpu_index / smp_threads) * spapr->vsmt + cpu_index % smp_threads
    (core_id / smp_threads) * spapr->vsmt (1 user)
    index * spapr->vsmt (2 users)

or guess that the VCPU id of a given VCPU is the first thread of a virtual
core:

    index % spapr->vsmt != 0

Even if the numbering logic isn't that complex, it is rather fragile to
have these assumptions open-coded in several places. FWIW this was
proved with recent issues related to VSMT.

This patch moves the VCPU id formula to a single function to be called
everywhere the code needs to compute one. It also adds an helper to
guess if a VCPU is the first thread of a VCORE.

Signed-off-by: Greg Kurz <gr...@kaod.org>
---
 hw/ppc/spapr.c |   29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 18ebc058acdd..800d3f001253 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -99,6 +99,20 @@
 
 #define PHANDLE_XICP            0x00001111
 
+/* These two functions implement the VCPU id numbering: one to compute them
+ * all and one to identify thread 0 of a VCORE. Any change to the first one
+ * is likely to have an impact on the second one, so let's keep them close.
+ */
+static int spapr_vcpu_id(sPAPRMachineState *spapr, int cpu_index)
+{
+    return
+        (cpu_index / smp_threads) * spapr->vsmt + cpu_index % smp_threads;
+}
+static bool spapr_is_vcore(sPAPRMachineState *spapr, PowerPCCPU *cpu)
+{
+    return spapr_get_vcpu_id(cpu) % spapr->vsmt == 0;
+}
+
 static ICSState *spapr_ics_create(sPAPRMachineState *spapr,
                                   const char *type_ics,
                                   int nr_irqs, Error **errp)
@@ -345,7 +359,7 @@ static int spapr_fixup_cpu_dt(void *fdt, sPAPRMachineState 
*spapr)
         int index = spapr_get_vcpu_id(cpu);
         int compat_smt = MIN(smp_threads, ppc_compat_max_vthreads(cpu));
 
-        if (index % spapr->vsmt != 0) {
+        if (!spapr_is_vcore(spapr, cpu)) {
             continue;
         }
 
@@ -630,7 +644,7 @@ static void spapr_populate_cpus_dt_node(void *fdt, 
sPAPRMachineState *spapr)
         DeviceClass *dc = DEVICE_GET_CLASS(cs);
         int offset;
 
-        if (index % spapr->vsmt != 0) {
+        if (!spapr_is_vcore(spapr, cpu)) {
             continue;
         }
 
@@ -2251,7 +2265,7 @@ static void spapr_init_cpus(sPAPRMachineState *spapr)
 
         if (mc->has_hotpluggable_cpus) {
             spapr_dr_connector_new(OBJECT(spapr), TYPE_SPAPR_DRC_CPU,
-                                   (core_id / smp_threads) * spapr->vsmt);
+                                   spapr_vcpu_id(spapr, core_id));
         }
 
         if (i < boot_cores_nr) {
@@ -3293,7 +3307,8 @@ void spapr_core_unplug_request(HotplugHandler 
*hotplug_dev, DeviceState *dev,
         return;
     }
 
-    drc = spapr_drc_by_id(TYPE_SPAPR_DRC_CPU, index * spapr->vsmt);
+    drc = spapr_drc_by_id(TYPE_SPAPR_DRC_CPU,
+                          spapr_vcpu_id(spapr, cc->core_id));
     g_assert(drc);
 
     spapr_drc_detach(drc);
@@ -3322,7 +3337,8 @@ static void spapr_core_plug(HotplugHandler *hotplug_dev, 
DeviceState *dev,
                    cc->core_id);
         return;
     }
-    drc = spapr_drc_by_id(TYPE_SPAPR_DRC_CPU, index * spapr->vsmt);
+    drc = spapr_drc_by_id(TYPE_SPAPR_DRC_CPU,
+                          spapr_vcpu_id(spapr, cc->core_id));
 
     g_assert(drc || !mc->has_hotpluggable_cpus);
 
@@ -3807,8 +3823,7 @@ void spapr_set_vcpu_id(PowerPCCPU *cpu, int cpu_index, 
Error **errp)
     sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
     int vcpu_id;
 
-    vcpu_id =
-        (cpu_index / smp_threads) * spapr->vsmt + cpu_index % smp_threads;
+    vcpu_id = spapr_vcpu_id(spapr, cpu_index);
 
     if (kvm_enabled() && !kvm_vcpu_id_is_valid(vcpu_id)) {
         error_setg(errp, "Can't create CPU with id %d in KVM", vcpu_id);