Re: [PATCH v2] xen: avoid crash in disable_hotplug_cpu

[Juergen Gross]

On 06/09/18 22:31, Olaf Hering wrote:
> Am Thu, 6 Sep 2018 14:45:57 -0400
> schrieb Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>:
> 
>> On 09/06/2018 02:37 AM, Olaf Hering wrote:
>>> The command 'xl vcpu-set 0 0', issued in dom0, will crash dom0:
> 
>>> This happens because handle_vcpu_hotplug_event is called twice. In the
>>> first iteration cpu_present is still true, in the second iteration
>>> cpu_present is false which causes get_cpu_device to return NULL.
>>> In case of cpu#0, cpu_online is apparently always true.
> 
>> I think we should check both this and num_online_cpus() != 0.
> 
> This can not possibly help. cpu#0 is the first one that goes offline.
> IF cpu0_hotpluggable is broken, then only "if (!cpu) return;" can help.

We should add the Xen PV guest test to arch_register_cpu() and switch
cpu0_hotpluggable off.


Juergen