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Subject: Re: [PATCH 6/6] KVM: VMX: enable IPI virtualization
To:     Zeng Guang <guang.zeng@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Luck, Tony" <tony.luck@intel.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Kim Phillips <kim.phillips@amd.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Jethro Beekman <jethro@fortanix.com>,
        "Huang, Kai" <kai.huang@intel.com>
Cc:     "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Hu, Robert" <robert.hu@intel.com>,
        "Gao, Chao" <chao.gao@intel.com>,
        Emanuele Giuseppe Esposito <eesposit@redhat.com>
References: <20210716064808.14757-1-guang.zeng@intel.com>
 <20210716064808.14757-7-guang.zeng@intel.com>
 <8aed2541-082d-d115-09ac-e7fcc05f96dc@redhat.com>
 <89f240cb-cb3a-c362-7ded-ee500cc12dc3@intel.com>
 <0d6f7852-95b3-d628-955b-f44d88a86478@redhat.com>
 <949abcb7-5f24-2107-a089-5e6c1bee8cf2@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <223af27a-2412-40f6-f4a6-e0a662041855@redhat.com>
Date:   Mon, 19 Jul 2021 15:58:17 +0200
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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);

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