linux-kernel - Re: [PATCH v5 7/8] KVM: VMX: Update PID-pointer table entry when APIC ID is changed

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Message-ID: <YeClaZWM1cM+WLjH@google.com>
Date:   Thu, 13 Jan 2022 22:19:21 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     Chao Gao <chao.gao@...el.com>, Zeng Guang <guang.zeng@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.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>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Hu, Robert" <robert.hu@...el.com>
Subject: Re: [PATCH v5 7/8] KVM: VMX: Update PID-pointer table entry when
 APIC ID is changed

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.