linux-kernel - Re: [PATCH 16/43] KVM: VMX: Stuff vcpu->arch.apic

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Date:   Tue, 25 May 2021 23:55:36 -0700
From:   Reiji Watanabe <reijiw@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     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,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/43] KVM: VMX: Stuff vcpu->arch.apic_base directly at
 vCPU RESET

On Fri, Apr 23, 2021 at 5:50 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Write vcpu->arch.apic_base directly instead of bouncing through
> kvm_set_apic_base().  This is a glorified nop, and is a step towards
> cleaning up the mess that is local APIC creation.
>
> When using an in-kernel APIC, kvm_create_lapic() explicitly sets
> vcpu->arch.apic_base to MSR_IA32_APICBASE_ENABLE to avoid its own
> kvm_lapic_set_base() call in kvm_lapic_reset() from triggering state
> changes.  That call during RESET exists purely to set apic->base_address
> to the default base value.  As a result, by the time VMX gets control,
> the only missing piece is the BSP bit being set for the reset BSP.
>
> For a userspace APIC, there are no side effects to process (for the APIC).
>
> In both cases, the call to kvm_update_cpuid_runtime() is a nop because
> the vCPU hasn't yet been exposed to userspace, i.e. there can't be any
> CPUID entries.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Reiji Watanabe <reijiw@...gle.com>