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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,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Tony Luck <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>,
        Kai Huang <kai.huang@intel.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        Robert Hu <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>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <0d6f7852-95b3-d628-955b-f44d88a86478@redhat.com>
Date:   Sun, 18 Jul 2021 22:32:38 +0200
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On 17/07/21 05:55, Zeng Guang wrote:
>>>      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 ?

Yes, possibly.  I'll look into using this idea for other parameters.

>>> +    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.

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.

Paolo