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diff --git a/sys/x86/x86/mp_x86.c b/sys/x86/x86/mp_x86.c
--- a/sys/x86/x86/mp_x86.c
+++ b/sys/x86/x86/mp_x86.c
@@ -871,6 +871,25 @@
nchildren = 0;
node = root;
while (node != NULL) {
+ /*
+ * When some APICs are disabled by tunables, nodes can end up
+ * with an empty cpuset. Nodes with an empty cpuset will be
+ * translated into cpu groups with empty cpusets. smp_topo_fill
+ * will then set cg_first and cg_last to -1. This isn't
+ * correctly handled in all functions. E.g. when
+ * cpu_search_lowest and cpu_search_highest loop through all
+ * cpus, they call CPU_ISSET on cpu -1 which ends up in a
+ * general protection fault.
+ *
+ * We could fix the scheduler to handle empty cpu groups
+ * correctly. Nevertheless, empty cpu groups are causing
+ * overhead for no value. So, it makes more sense to just don't
+ * create them.
+ */
+ if (CPU_EMPTY(&node->cpuset)) {
+ node = topo_next_node(root, node);
+ continue;
+ }
if (CPU_CMP(&node->cpuset, &root->cpuset) == 0) {
if (node->type == TOPO_TYPE_CACHE &&
cg_root->cg_level < node->subtype)
@@ -896,8 +915,14 @@
if (nchildren == root->cpu_count)
return;
- cg_root->cg_child = smp_topo_alloc(nchildren);
+ /*
+ * We are not interested in nodes without children.
+ */
cg_root->cg_children = nchildren;
+ if (nchildren == 0)
+ return;
+
+ cg_root->cg_child = smp_topo_alloc(nchildren);
/*
* Now find again the same cache nodes as above and recursively
@@ -909,7 +934,8 @@
if ((node->type != TOPO_TYPE_GROUP &&
node->type != TOPO_TYPE_NODE &&
node->type != TOPO_TYPE_CACHE) ||
- CPU_CMP(&node->cpuset, &root->cpuset) == 0) {
+ CPU_CMP(&node->cpuset, &root->cpuset) == 0 ||
+ CPU_EMPTY(&node->cpuset)) {
node = topo_next_node(root, node);
continue;
}

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