linux-kernel - [PATCH 1/2] KVM: SVM: Initialize AVIC VMCB fields if AVIC is enabled with in-kernel APIC

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Message-ID: <20260203190711.458413-2-seanjc@google.com>
Date: Tue,  3 Feb 2026 11:07:09 -0800
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, 
	Jim Mattson <jmattson@...gle.com>, Naveen N Rao <naveen@...nel.org>, 
	"Maciej S . Szmigiero" <maciej.szmigiero@...cle.com>
Subject: [PATCH 1/2] KVM: SVM: Initialize AVIC VMCB fields if AVIC is enabled
 with in-kernel APIC

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@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/avic.c | 2 +-
 arch/x86/kvm/svm/svm.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index f92214b1a938..44e07c27b190 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -368,7 +368,7 @@ void avic_init_vmcb(struct vcpu_svm *svm, struct vmcb *vmcb)
 	vmcb->control.avic_physical_id = __sme_set(__pa(kvm_svm->avic_physical_id_table));
 	vmcb->control.avic_vapic_bar = APIC_DEFAULT_PHYS_BASE;

-	if (kvm_apicv_activated(svm->vcpu.kvm))
+	if (kvm_vcpu_apicv_active(&svm->vcpu))
 		avic_activate_vmcb(svm);
 	else
 		avic_deactivate_vmcb(svm);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 5f0136dbdde6..e8313fdc5465 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1189,7 +1189,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu, bool init_event)
 	if (guest_cpu_cap_has(vcpu, X86_FEATURE_ERAPS))
 		svm->vmcb->control.erap_ctl |= ERAP_CONTROL_ALLOW_LARGER_RAP;

-	if (kvm_vcpu_apicv_active(vcpu))
+	if (enable_apicv && irqchip_in_kernel(vcpu->kvm))
 		avic_init_vmcb(svm, vmcb);

 	if (vnmi)
-- 
2.53.0.rc2.204.g2597b5adb4-goog