linux-kernel - Re: [PATCH v2 3/3] KVM: SVM: Add irqchip

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Date:   Fri, 15 Sep 2017 12:21:15 -0700
From:   Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, joro@...tes.org
Subject: Re: [PATCH v2 3/3] KVM: SVM: Add irqchip_split() checks before
 enabling AVIC

Radim,

On 9/14/17 08:23, Suravee Suthikulpanit wrote:
> Radim,
>
> On 9/14/17 08:20, Radim Krčmář wrote:
>>> @@ -1594,6 +1593,12 @@ static int avic_init_vcpu(struct vcpu_svm *svm)
>>>      if (!avic)
>>>          return 0;
>>>
>>> +    if (!kvm_vcpu_apicv_active(&svm->vcpu)) {
>>> +        pr_debug("%s: Disable AVIC due to non-split irqchip.\n",
>>> +                  __func__);
>> We need to have an extra condition just because of this print ...
>> I removed the print altogether when applying -- I thought more about
>> that and it was aimed at people who wonder why AVIC was suddenly
>> disabled and it's unlikely that they will enable a debug message without
>> already knowing the reason,
>
> Make sense. Thanks.
>
>>
>> thanks.
>>
>>> @@ -4388,7 +4393,7 @@ static void svm_set_virtual_x2apic_mode(struct kvm_vcpu
>>> *vcpu, bool set)
>>>
>>>  static bool svm_get_enable_apicv(struct kvm_vcpu *vcpu)
>>>  {
>> A close contender was pr_info_once() here:
>>
>>     if (avic && !irqchip_split(vcpu->kvm))
>>         pr_info_once(...)
>>
>
> Looks good.

Actually, thinking about it again, this would not work either since 
pr_xxx_once() would only print the message once per loading of kvm_amd module. 
However, we would prefer the message to be printed per VM initialization. I also 
tried adding the check and print this message in the kvm_x86_ops.vm_init(), but 
this also does not work since the vm_init() function is called before the 
kvm_vm_ioctl_enable_cap(KVM_CAP_SPLIT_IRQCHIP).

Therefore, pr_info() might be better here, even though this would get print per 
VCPU initialization. Any other suggestions?

Thanks,
Suravee