Date:   Fri, 14 Jan 2022 10:58:27 +0800
From:   Chao Gao <chao.gao@intel.com>
To:     Sean Christopherson <seanjc@google.com>
Cc:     Maxim Levitsky <mlevitsk@redhat.com>,
        Zeng Guang <guang.zeng@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Paolo Bonzini <pbonzini@redhat.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>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Hu, Robert" <robert.hu@intel.com>
Subject: Re: [PATCH v5 7/8] KVM: VMX: Update PID-pointer table entry when
 APIC ID is changed
Message-ID: <20220114025825.GA3010@gao-cwp>
References: <20211231142849.611-1-guang.zeng@intel.com>
 <20211231142849.611-8-guang.zeng@intel.com>
 <640e82f3-489d-60af-1d31-25096bef1a46@amd.com>
 <4eee5de5-ab76-7094-17aa-adc552032ba0@intel.com>
 <aa86022c-2816-4155-8d77-f4faf6018255@amd.com>
 <aa7db6d2-8463-2517-95ce-c0bba22e80d4@intel.com>
 <d058f7464084cadc183bd9dbf02c7f525bb9f902.camel@redhat.com>
 <20220110074523.GA18434@gao-cwp>
 <1ff69ed503faa4c5df3ad1b5abe8979d570ef2b8.camel@redhat.com>
 <YeClaZWM1cM+WLjH@google.com>
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On Thu, Jan 13, 2022 at 10:19:21PM +0000, Sean Christopherson wrote:
>On Tue, Jan 11, 2022, Maxim Levitsky wrote:
>> Both Intel and AMD's PRM also state that changing APIC ID is implementation
>> dependent.
>>  
>> I vote to forbid changing apic id, at least in the case any APIC acceleration
>> is used, be that APICv or AVIC.
>
>That has my vote as well.  For IPIv in particular there's not much concern with
>backwards compability, i.e. we can tie the behavior to enable_ipiv.

Hi Sean and Levitsky,

Let's align on the implementation.

To disable changes for xAPIC ID when IPIv/AVIC is enabled:

1. introduce a variable (forbid_apicid_change) for this behavior in kvm.ko
and export it so that kvm-intel, kvm-amd can set it when IPIv/AVIC is
enabled. To reduce complexity, this variable is a module level setting.

2. when guest attempts to change xAPIC ID but it is forbidden, KVM prints
a warning on host and injects a #GP to guest.

3. remove AVIC code that deals with changes to xAPIC ID.