linux-kernel - Re: [PATCH v2 2/4] KVM: x86: replace kvm_apic_id with kvm_{x,x2}apic

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Date:   Wed, 14 Dec 2016 18:15:36 +0100
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Igor Mammedov <imammedo@...hat.com>
Subject: Re: [PATCH v2 2/4] KVM: x86: replace kvm_apic_id with
 kvm_{x,x2}apic_id

2016-12-14 17:59+0100, Paolo Bonzini:
> On 14/12/2016 17:15, David Hildenbrand wrote:
>> 
>>>      kvm_for_each_vcpu(i, vcpu, kvm)
>>>          if (kvm_apic_present(vcpu))
>>> -            max_id = max(max_id, kvm_apic_id(vcpu->arch.apic));
>>> +            max_id = max(max_id, kvm_x2apic_id(vcpu->arch.apic));
>>>
>>>      new = kvm_kvzalloc(sizeof(struct kvm_apic_map) +
>>>                         sizeof(struct kvm_lapic *) * ((u64)max_id + 1));
>>> @@ -179,16 +189,23 @@ static void recalculate_apic_map(struct kvm *kvm)
>>>          struct kvm_lapic *apic = vcpu->arch.apic;
>>>          struct kvm_lapic **cluster;
>>>          u16 mask;
>>> -        u32 ldr, aid;
>>> +        u32 ldr;
>>> +        u8 xapic_id;
>>> +        u32 x2apic_id;
>>>
>>>          if (!kvm_apic_present(vcpu))
>>>              continue;
>>>
>>> -        aid = kvm_apic_id(apic);
>> 
>> think I'd even prefer here a simple
>> 
>> aid = kvm_xapic_id(apic);
>> if (apic_x2apic_mode(apic))
>>     aid = kvm_x2apic_id(apic);
>> 
>> that would keep changes minimal and I don't really see any benefit in
>> the code when splitting handling up.
>> 
>> Patch 4 then simply can fixup setting code
>> 
>> if (aid <= new->max_apic_id && !new->phys_map[aid])
>>     new->phys_map[aid] = apic;
>> 
>> (if I am not missing some important corner case here)
> 
> Radim, what do you think?  I wanted to get these in before Christmas,
> but it's your call.

There was a reason why it was so ugly ... it's not a hack for nothing.

I can hope to make the patches/code more understandable, but the
function shouldn't change, unless we want to take a different approach.