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

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Message-ID: <35f6b1f8-6769-935e-633f-9013e496af16@redhat.com>
Date:   Wed, 14 Dec 2016 17:59:19 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Hildenbrand <david@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Igor Mammedov <imammedo@...hat.com>
Subject: Re: [PATCH v2 2/4] KVM: x86: replace kvm_apic_id with
 kvm_{x,x2}apic_id



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.

Paolo

> 
>> -        ldr = kvm_lapic_get_reg(apic, APIC_LDR);
>> +        xapic_id = kvm_xapic_id(apic);
>> +        x2apic_id = kvm_x2apic_id(apic);
>>
>> -        if (aid <= new->max_apic_id)
>> -            new->phys_map[aid] = apic;
>> +        if (apic_x2apic_mode(apic) &&
>> +                x2apic_id <= new->max_apic_id)
>> +            new->phys_map[x2apic_id] = apic;
>> +        else if (!apic_x2apic_mode(apic))
> 
> 
> This looks good to me.
>