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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 19 Jul 2021 15:58:17 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Zeng Guang <guang.zeng@...el.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 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