Both VMX and SVM require per-cpu memory allocation, which is done at module
init time, for only online cpus.
Backend was not allocating enough structure for all possible CPUs, so
new CPUs coming online could not be hardware enabled.
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e27b7a9..2cd8bc2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1716,9 +1716,6 @@ static int kvm_cpu_hotplug(struct notifier_block *notifier, unsigned long val,
{
int cpu = (long)v;
- if (!kvm_usage_count)
- return NOTIFY_OK;
-
val&= ~CPU_TASKS_FROZEN;
switch (val) {
case CPU_DYING: