linux-kernel - [PATCH v2 2/9] KVM: x86: Drop superfluous kvm_lapic_set

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Message-ID: <20241101183555.1794700-3-seanjc@google.com>
Date: Fri,  1 Nov 2024 11:35:48 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Kai Huang <kai.huang@...el.com>
Subject: [PATCH v2 2/9] KVM: x86: Drop superfluous kvm_lapic_set_base() call
 when setting APIC state

Now that kvm_lapic_set_base() does nothing if the "new" APIC base MSR is
the same as the current value, drop the kvm_lapic_set_base() call in the
KVM_SET_LAPIC flow that passes in the current value, as it too does
nothing.

Note, the purpose of invoking kvm_lapic_set_base() was purely to set
apic->base_address (see commit 5dbc8f3fed0b ("KVM: use kvm_lapic_set_base()
to change apic_base")).  And there is no evidence that explicitly setting
apic->base_address in KVM_SET_LAPIC ever had any functional impact; even
in the original commit 96ad2cc61324 ("KVM: in-kernel LAPIC save and restore
support"), all flows that set apic_base also set apic->base_address to the
same address.  E.g. svm_create_vcpu() did open code a write to apic_base,

	svm->vcpu.apic_base = 0xfee00000 | MSR_IA32_APICBASE_ENABLE;

but it also called kvm_create_lapic() when irqchip_in_kernel() is true.

Reviewed-by: Kai Huang <kai.huang@...el.com>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
Link: https://lore.kernel.org/r/20241009181742.1128779-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/lapic.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 8fe63f719254..9f88a49654b0 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -3060,7 +3060,6 @@ int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)

 	kvm_x86_call(apicv_pre_state_restore)(vcpu);

-	kvm_lapic_set_base(vcpu, vcpu->arch.apic_base);
 	/* set SPIV separately to get count of SW disabled APICs right */
 	apic_set_spiv(apic, *((u32 *)(s->regs + APIC_SPIV)));

-- 
2.47.0.163.g1226f6d8fa-goog