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

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Date:   Sat, 17 Jul 2021 11:55:37 +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,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <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>,
        Kai Huang <kai.huang@...el.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Robert Hu <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 7/16/2021 5:52 PM, Paolo Bonzini wrote:
> On 16/07/21 08:48, Zeng Guang wrote:
>>
>> +    if (!(_cpu_based_3rd_exec_control & TERTIARY_EXEC_IPI_VIRT))
>> +        enable_ipiv = 0;
>> +
>>       }
>
> Please move this to hardware_setup(), using a new function 
> cpu_has_vmx_ipiv() in vmx/capabilities.h.
>
ok, we will change it to follow current framework.
>>      if (_cpu_based_exec_control & 
>> CPU_BASED_ACTIVATE_TERTIARY_CONTROLS) {
>> -        u64 opt3 = 0;
>> +        u64 opt3 = enable_ipiv ? TERTIARY_EXEC_IPI_VIRT : 0;
>>          u64 min3 = 0;
>
> I like the idea of changing opt3, but it's different from how 
> setup_vmcs_config works for the other execution controls.  Let me 
> think if it makes sense to clean this up, and move the handling of 
> other module parameters from hardware_setup() to setup_vmcs_config().
>
May be an exception for ipiv feature ?
>> +
>> +    if (vmx->ipiv_active)
>> +        install_pid(vmx);
>
> This should be if (enable_ipiv) instead, I think.
>
> In fact, in all other places that are using vmx->ipiv_active, you can 
> actually replace it with enable_ipiv; they are all reached only with 
> kvm_vcpu_apicv_active(vcpu) == true.
>
enable_ipiv as a global variable indicates the hardware capability to 
enable IPIv. Each VM may have different IPIv configuration according to 
kvm_vcpu_apicv_active status. So we use ipiv_active per VM to enclose 
IPIv related operations.
>> +    if (!enable_apicv) {
>> +        enable_ipiv = 0;
>> +        vmcs_config.cpu_based_3rd_exec_ctrl &= ~TERTIARY_EXEC_IPI_VIRT;
>> +    }
>
> The assignment to vmcs_config.cpu_based_3rd_exec_ctrl should not be 
> necessary; kvm_vcpu_apicv_active will always be false in that case and 
> IPI virtualization would never be enabled.
>
We originally intend to make vmcs_config consistent with the actual ipiv 
capability and decouple it from other factors. As you mentioned , it's 
not necessary to update vmcs_config.cpu_based_3rd_exec_ctrl in this 
case. We will remove it.

Thanks.

> Paolo
>