linux-kernel - Re: [RFC PATCH 06/13] KVM: SVM: Add logic to determine x2APIC mode

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Date:   Thu, 3 Mar 2022 20:12:11 +0700
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     pbonzini@...hat.com, seanjc@...gle.com, joro@...tes.org,
        jon.grimm@....com, wei.huang2@....com, terry.bowman@....com
Subject: Re: [RFC PATCH 06/13] KVM: SVM: Add logic to determine x2APIC mode

Hi Maxim

On 2/25/22 12:29 AM, Maxim Levitsky wrote:
>> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
>> index 1a0bf6b853df..bfbebb933da2 100644
>> --- a/arch/x86/kvm/svm/svm.h
>> +++ b/arch/x86/kvm/svm/svm.h
>> @@ -225,6 +225,7 @@ struct vcpu_svm {
>>   	u32 dfr_reg;
>>   	struct page *avic_backing_page;
>>   	u64 *avic_physical_id_cache;
>> +	bool x2apic_enabled;
>>   
>>   	/*
>>   	 * Per-vcpu list of struct amd_svm_iommu_ir:
>> @@ -566,6 +567,7 @@ void avic_init_vmcb(struct vcpu_svm *svm);
>>   int avic_incomplete_ipi_interception(struct kvm_vcpu *vcpu);
>>   int avic_unaccelerated_access_interception(struct kvm_vcpu *vcpu);
>>   int avic_init_vcpu(struct vcpu_svm *svm);
>> +void avic_update_vapic_bar(struct vcpu_svm *svm, u64 data);
>>   void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
>>   void avic_vcpu_put(struct kvm_vcpu *vcpu);
>>   void avic_post_state_restore(struct kvm_vcpu *vcpu);
>
>  ....
>
> I also don't think you need x2apic_enabled boolean.
> You can already know if a vCPU uses apic or x2apic via
> 
> kvm_get_apic_mode(vcpu);
> 
> in fact I don't think avic code should have any bookeeping in regard to x2apic/x2avic mode,
> but rather kvm's apic mode  (which is read directly from apic base msr (vcpu->arch.apic_base),
> should enable avic, or x2avic if possible, or inhibit avic if not possible.
> 
> e.g it should drive the bits in vmcb and such.

I'll also clean this up in V2.

Regards,
Suravee