linux-kernel - [PATCH v2 12/46] KVM: x86: Remove defunct BSP "update" in local APIC reset

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Date:   Tue, 13 Jul 2021 09:32:50 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.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, Reiji Watanabe <reijiw@...gle.com>
Subject: [PATCH v2 12/46] KVM: x86: Remove defunct BSP "update" in local APIC reset

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.

Reviewed-by: Reiji Watanabe <reijiw@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/lapic.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index add4dd1e3528..a24ce8fe93e5 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2367,9 +2367,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
 	apic->highest_isr_cache = -1;
 	update_divide_count(apic);
 	atomic_set(&apic->lapic_timer.pending, 0);
-	if (kvm_vcpu_is_bsp(vcpu))
-		kvm_lapic_set_base(vcpu,
-				vcpu->arch.apic_base | MSR_IA32_APICBASE_BSP);
+
 	vcpu->arch.pv_eoi.msr_val = 0;
 	apic_update_ppr(apic);
 	if (vcpu->arch.apicv_active) {
-- 
2.32.0.93.g670b81a890-goog