KVM: SVM: Initialize AVIC VMCB fields if AVIC is enabled with in-kernel APIC

commit 3989a6d upstream.

Initialize all per-vCPU AVIC control fields in the VMCB if AVIC is enabled
in KVM and the VM has an in-kernel local APIC, i.e. if it's _possible_ the
vCPU could activate AVIC at any point in its lifecycle.  Configuring the
VMCB if and only if AVIC is active "works" purely because of optimizations
in kvm_create_lapic() to speculatively set apicv_active if AVIC is enabled
*and* to defer updates until the first KVM_RUN.  In quotes because KVM
likely won't do the right thing if kvm_apicv_activated() is false, i.e. if
a vCPU is created while APICv is inhibited at the VM level for whatever
reason.  E.g. if the inhibit is *removed* before KVM_REQ_APICV_UPDATE is
handled in KVM_RUN, then __kvm_vcpu_update_apicv() will elide calls to
vendor code due to seeing "apicv_active == activate".

Cleaning up the initialization code will also allow fixing a bug where KVM
incorrectly leaves CR8 interception enabled when AVIC is activated without
creating a mess with respect to whether AVIC is activated or not.

Cc: stable@vger.kernel.org
Fixes: 67034bb ("KVM: SVM: Add irqchip_split() checks before enabling AVIC")
Fixes: 6c3e442 ("svm: Add support for dynamic APICv")
Reviewed-by: Naveen N Rao (AMD) <naveen@kernel.org>
Reviewed-by: Jim Mattson <jmattson@google.com>
Link: https://patch.msgid.link/20260203190711.458413-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: sean-jc

arch/x86/kvm/svm/avic.c

@@ -253,7 +253,7 @@ void avic_init_vmcb(struct vcpu_svm *svm, struct vmcb *vmcb)
 	vmcb->control.avic_physical_id = ppa & AVIC_HPA_MASK;
 	vmcb->control.avic_vapic_bar = APIC_DEFAULT_PHYS_BASE & VMCB_AVIC_APIC_BAR_MASK;
 
-	if (kvm_apicv_activated(svm->vcpu.kvm))
+	if (kvm_vcpu_apicv_active(&svm->vcpu))
 		avic_activate_vmcb(svm);
 	else
 		avic_deactivate_vmcb(svm);

arch/x86/kvm/svm/svm.c

@@ -1360,7 +1360,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
 	if (boot_cpu_has(X86_FEATURE_V_SPEC_CTRL))
 		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SPEC_CTRL, 1, 1);
 
-	if (kvm_vcpu_apicv_active(vcpu))
+	if (enable_apicv && irqchip_in_kernel(vcpu->kvm))
 		avic_init_vmcb(svm, vmcb);
 
 	if (vnmi)