linux-kernel - Re: [RFC PATCH v3 23/59] KVM: x86: Allow host-initiated WRMSR to set X2APIC regardless of CPUID

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Message-ID: <87fsrkja4j.ffs@tglx>
Date:   Thu, 25 Nov 2021 20:41:48 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     isaku.yamahata@...el.com, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.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>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     isaku.yamahata@...el.com, isaku.yamahata@...il.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [RFC PATCH v3 23/59] KVM: x86: Allow host-initiated WRMSR to
 set X2APIC regardless of CPUID

On Wed, Nov 24 2021 at 16:20, isaku yamahata wrote:
> Let userspace, or in the case of TDX, KVM itself, enable X2APIC even if
> X2APIC is not reported as supported in the guest's CPU model.  KVM
> generally does not force specific ordering between ioctls(), e.g. this
> forces userspace to configure CPUID before MSRs.  And for TDX, vCPUs
> will always run with X2APIC enabled, e.g. KVM will want/need to enable
> X2APIC from time zero.

This is complete crap. Fix the broken user space and do not add
horrible hacks to the kernel.

Thanks,

        tglx