linux-kernel - Re: [PATCH] KVM: SVM: compile out AVIC if !CONFIG_X86_LOCAL

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Date:	Wed, 15 Jun 2016 00:01:17 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Suravee Suthikulanit <suravee.suthikulpanit@....com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	rkrcmar@...hat.com
Subject: Re: [PATCH] KVM: SVM: compile out AVIC if !CONFIG_X86_LOCAL_APIC



On 14/06/2016 23:44, Suravee Suthikulanit wrote:
> On 6/14/2016 4:22 PM, Paolo Bonzini wrote:
>> ----- Original Message -----
>>> From: "Suravee Suthikulanit" <suravee.suthikulpanit@....com>
>>> To: "Paolo Bonzini" <pbonzini@...hat.com>,
>>> linux-kernel@...r.kernel.org, kvm@...r.kernel.org
>>> Cc: rkrcmar@...hat.com
>>> Sent: Tuesday, June 14, 2016 8:20:30 PM
>>> Subject: Re: [PATCH] KVM: SVM: compile out AVIC if
>>> !CONFIG_X86_LOCAL_APIC
>>>
>>> Hi Paolo,
>>>
>>> On 6/14/2016 11:40 AM, Paolo Bonzini wrote:
>>>> AVIC needs __default_cpu_present_to_apicid.  Stub out all functions
>>>> that use it, and disable the module parameter, if Linux is
>>>> compiled without local APIC support.
>>>
>>> I think you are right that we should disable AVIC #ifndef
>>> CONFIG_X86_LOCAL_APIC. However, do you think we should just use
>>> default_cpu_present_to_apicid() instead of the
>>> __default_cpu_present_to_apicid()?
>>
>> I'm not sure why that would help?  default_cpu_present_to_apicid
>> is also declared only if CONFIG_X86_LOCAL_APIC is defined.
> 
> Actually, I also meant to include the change that I sent out
> (https://lkml.org/lkml/2016/6/13/898), which declares a dummy for the
> case #ifndef CONFIG_X86_LOCAL_APIC.  That should help with the issue here.

I think it is by design that default_cpu_present_to_apicid() is absent.

Perhaps you could create a kvm_cpu_get_apicid() function that is either
__default_cpu_present_to_apicid() or WARN_ON_ONCE(1)+return 0?

Paolo