Re: [PATCH 12/43] KVM: x86: Remove defunct BSP "update" in local APIC reset

[Reiji Watanabe]

On Fri, Apr 23, 2021 at 5:49 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Remove a BSP APIC update in kvm_lapic_reset() that is a glorified and
> confusing nop.  When the code was originally added, kvm_vcpu_is_bsp()
> queried kvm->arch.bsp_vcpu, i.e. the intent was to set the BSP bit in the
> BSP vCPU's APIC.  But, stuffing the BSP bit at INIT was wrong since the
> guest can change its BSP(s); this was fixed by commit 58d269d8cccc ("KVM:
> x86: BSP in MSR_IA32_APICBASE is writable").
>
> In other words, kvm_vcpu_is_bsp() is now purely a reflection of
> vcpu->arch.apic_base.MSR_IA32_APICBASE_BSP, thus the update will always
> set the current value and kvm_lapic_set_base() is effectively a nop if
> the new and old values match.  The RESET case, which does need to stuff
> the BSP for the reset vCPU, is handled by vendor code (though this will
> soon be moved to common code).
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Reiji Watanabe <reijiw@xxxxxxxxxx>