Re: [PATCH v5] x86: call smp vmxoff in smp stop
- Date: Thu, 20 Apr 2017 12:13:01 +0200
- From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
- Subject: Re: [PATCH v5] x86: call smp vmxoff in smp stop
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
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.