linux-kernel - Re: [PATCH v5] x86: call smp vmxoff in smp stop

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Date:   Thu, 20 Apr 2017 13:09:36 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     mingo@...nel.org, x86@...nel.org,
        Tiantian Feng <fengtiantian@...wei.com>,
        Xishi Qiu <qiuxishi@...wei.com>
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@...wei.com>
>>>
>>> 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@...hat.com>

-- 

Thanks,

David