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pc: make sure that guest isn't able to unplug the first cpu 

The first cpu unplug wasn't ever supported and corresponding
monitor/qmp commands refuse to unplug it. However guest is able
to issue eject request either using following command:
  # echo 1 >/sys/devices/system/cpu/cpu0/firmware_node/eject
or directly writing to cpu hotplug registers, which makes
qemu crash with SIGSEGV following back trace:

   kvm_flush_coalesced_mmio_buffer ()
       while (ring->first != ring->last)
   ...
   qemu_flush_coalesced_mmio_buffer
   prepare_mmio_access
   flatview_read_continue
   flatview_read
   address_space_read_full
   address_space_rw
   kvm_cpu_exec(cpu!0)
   qemu_kvm_cpu_thread_fn

the reason for which is that ring == KVMState::coalesced_mmio_ring
happens to be a part of 1st CPU that was uplugged by guest.

Fix it by forbidding 1st cpu unplug from guest side and in addition
remove CPU0._EJ0 ACPI method to make clear that unplug of the first
CPU is not supported.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Igor Mammedov 2018-08-27 13:07:10 +02:00 committed by Michael S. Tsirkin
parent 6755e618d0
commit c2d2a81b41
1 changed files with 6 additions and 4 deletions
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10
hw/acpi/cpu.c
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@ -117,7 +117,7 @@ static void cpu_hotplug_wr(void *opaque, hwaddr addr, uint64_t data,
DeviceState *dev = NULL;
HotplugHandler *hotplug_ctrl = NULL;
if (!cdev->cpu) {
if (!cdev->cpu || cdev->cpu == first_cpu) {
trace_cpuhp_acpi_ejecting_invalid_cpu(cpu_st->selector);
break;
}
@ -541,9 +541,11 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
aml_buffer(madt_buf->len, (uint8_t *)madt_buf->data)));
g_array_free(madt_buf, true);
method = aml_method("_EJ0", 1, AML_NOTSERIALIZED);
aml_append(method, aml_call1(CPU_EJECT_METHOD, uid));
aml_append(dev, method);
if (CPU(arch_ids->cpus[i].cpu) != first_cpu) {
method = aml_method("_EJ0", 1, AML_NOTSERIALIZED);
aml_append(method, aml_call1(CPU_EJECT_METHOD, uid));
aml_append(dev, method);
}
method = aml_method("_OST", 3, AML_SERIALIZED);
aml_append(method,