Re: [PATCH v5] x86: call smp vmxoff in smp stop
- Date: Thu, 20 Apr 2017 13:09:36 +0200
- From: David Hildenbrand <david@xxxxxxxxxx>
- Subject: Re: [PATCH v5] x86: call smp vmxoff in smp stop
On 20.04.2017 12:13, Paolo Bonzini wrote:
> On 20/04/2017 12:01, David Hildenbrand wrote:
>> On 19.04.2017 18:18, Paolo Bonzini wrote:
>>> From: Tiantian Feng <fengtiantian@xxxxxxxxxx>
>>> A CPU in VMX root mode will ignore INIT signals and fail to bring
>>> up the APs after reboot. Therefore, on a panic we disable VMX on all
>>> CPUs before rebooting or triggering kdump.
>>> Do this when halting the machine as well, in case a firmware-level reboot
>>> does not perform a cold reset for all processors. Without doing this,
>>> rebooting the host may hang.
>> Guess this make sense, just wonder if something like that is actually
>> expected to work? Not doing a cold reset feels like leaving a lot of
>> stuff in an uninitialized state. Shouldn't that specific firmware then
>> care about performing any necessary resets?
> Yes, but it cannot do them if it cannot even perform the initial warm
> reset ("INIT").
> It's probably rare, after all the original introduction of
> cpu_emergency_vmxoff is as old as 2008 and it took nine years for
> someone to think of making this extra change.
Right, so this is really a special case. I think this is just fine.
The same problem with !vmm_exclusive as with other callers of
cpu_emergency_vmxoff(), but that should be solved as soon as
vmm_exclusive is dropped.
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>