[Qemu-devel] [PATCH] pseries: do not allow memory-less/cpu-less NUMA node

[Laurent Vivier <lvivier@redhat.com>]

When we hotplug a CPU on memory-less/cpu-less node, the linux kernel
crashes.

This happens because linux kernel needs to know the NUMA topology at
start to be able to initialize the distance lookup table.

On pseries, the topology is provided by the firmware via the existing
CPUs and memory information. Thus a node without memory and CPU cannot be
discovered by the kernel.

To avoid the kernel crash, do not allow to start pseries with empty
nodes.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/ppc/spapr.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index baedadf20b8c..8be738901cf9 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -2847,6 +2847,39 @@ static void spapr_machine_init(MachineState *machine)
     /* init CPUs */
     spapr_init_cpus(spapr);
 
+    /*
+     * check we don't have a memory-less/cpu-less NUMA node
+     * Firmware relies on the existing memory/cpu topology to provide the
+     * NUMA topology to the kernel.
+     * And the linux kernel needs to know the NUMA topology at start
+     * to be able to hotplug CPUs later.
+     */
+    if (nb_numa_nodes) {
+        for (i = 0; i < nb_numa_nodes; ++i) {
+            /* check for memory-less node */
+            if (numa_info[i].node_mem == 0) {
+                CPUState *cs;
+                int found = 0;
+                /* check for cpu-less node */
+                CPU_FOREACH(cs) {
+                    PowerPCCPU *cpu = POWERPC_CPU(cs);
+                    if (cpu->node_id == i) {
+                        found = 1;
+                        break;
+                    }
+                }
+                /* memory-less and cpu-less node */
+                if (!found) {
+                    error_report(
+                       "Memory-less/cpu-less nodes are not supported (node %d)",
+                                 i);
+                    exit(1);
+                }
+            }
+        }
+
+    }
+
     if ((!kvm_enabled() || kvmppc_has_cap_mmu_radix()) &&
         ppc_type_check_compat(machine->cpu_type, CPU_POWERPC_LOGICAL_3_00, 0,
                               spapr->max_compat_pvr)) {
-- 
2.21.0