linux-kernel - Re: [PATCH 6/6] KVM: VMX: enable IPI virtualization

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Date:   Tue, 20 Jul 2021 09:07:22 +0800
From:   Zeng Guang <guang.zeng@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Kim Phillips <kim.phillips@....com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jethro Beekman <jethro@...tanix.com>,
        "Huang, Kai" <kai.huang@...el.com>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Hu, Robert" <robert.hu@...el.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        Emanuele Giuseppe Esposito <eesposit@...hat.com>
Subject: Re: [PATCH 6/6] KVM: VMX: enable IPI virtualization

On 7/19/2021 9:58 PM, Paolo Bonzini wrote:
> On 19/07/21 14:38, Zeng Guang wrote:
>>> Understood, but in practice all uses of vmx->ipiv_active are
>>> guarded by kvm_vcpu_apicv_active so they are always reached with
>>> vmx->ipiv_active == enable_ipiv.
>>>
>>> The one above instead seems wrong and should just use enable_ipiv.
>> enable_ipiv associate with "IPI virtualization" setting in tertiary
>> exec controls and enable_apicv which depends on cpu_has_vmx_apicv().
>> kvm_vcpu_apicv_active still can be false even if enable_ipiv is true,
>> e.g. in case irqchip not emulated in kernel.
> Right, kvm_vcpu_apicv_active *is* set in init_vmcs.  But there's an
>       "if (kvm_vcpu_apicv_active(&vmx->vcpu))" above.  You can just stick
>
> 	if (enable_ipicv)
> 		install_pid(vmx);
Ok, got your point now. I will revise to remove vmx->ipiv_active. Thanks.
> inside there.  As to the other occurrences of vmx->ipiv_active, look here:
>
>> +	if (!kvm_vcpu_apicv_active(vcpu))
>> +		return;
>> +
>> +	if ((!kvm_arch_has_assigned_device(vcpu->kvm) ||
>> +		!irq_remapping_cap(IRQ_POSTING_CAP)) &&
>> +		!to_vmx(vcpu)->ipiv_active)
>>   		return;
>>   
> This one can be enable_ipiv because APICv must be active.
>
>> +	if (!kvm_vcpu_apicv_active(vcpu))
>> +		return 0;
>> +
>> +	/* Put vCPU into a list and set NV to wakeup vector if it is
>> +	 * one of the following cases:
>> +	 * 1. any assigned device is in use.
>> +	 * 2. IPI virtualization is enabled.
>> +	 */
>> +	if ((!kvm_arch_has_assigned_device(vcpu->kvm) ||
>> +		!irq_remapping_cap(IRQ_POSTING_CAP)) && !to_vmx(vcpu)->ipiv_active)
>>   		return 0;
> This one can be !enable_ipiv because APICv must be active.
>
>> @@ -3870,6 +3877,8 @@ static void vmx_update_msr_bitmap_x2apic(struct kvm_vcpu *vcpu, u8 mode)
>>   		vmx_enable_intercept_for_msr(vcpu, X2APIC_MSR(APIC_TMCCT), MSR_TYPE_RW);
>>   		vmx_disable_intercept_for_msr(vcpu, X2APIC_MSR(APIC_EOI), MSR_TYPE_W);
>>   		vmx_disable_intercept_for_msr(vcpu, X2APIC_MSR(APIC_SELF_IPI), MSR_TYPE_W);
>> +		vmx_set_intercept_for_msr(vcpu, X2APIC_MSR(APIC_ICR),
>> +				MSR_TYPE_RW, !to_vmx(vcpu)->ipiv_active);
>>   	}
>>   }
> Is inside "if (mode & MSR_BITMAP_MODE_X2APIC_APICV)" so APICv must be
> activ; so it can be enable_ipiv as well.
>
> In conclusion, you do not need vmx->ipiv_active.
>
> Paolo
>