linux-kernel - [PATCH 4/4] KVM: VMX: Register posted interrupt wakeup handler iff APICv is enabled

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Date:   Fri,  8 Oct 2021 17:11:07 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        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>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: [PATCH 4/4] KVM: VMX: Register posted interrupt wakeup handler iff
 APICv is enabled

Don't bother registering a posted interrupt wakeup handler if APICv is
disabled, KVM utilizes the wakeup vector if and only if APICv is enabled.
Practically speaking, there's no meaningful functional change as KVM's
wakeup handler is a glorified nop if there are no vCPUs using posted
interrupts, not to mention that nothing in the system should be sending
wakeup interrupts when APICv is disabled.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9164f1870d49..df9ad4675215 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7553,7 +7553,8 @@ static void vmx_migrate_timers(struct kvm_vcpu *vcpu)
 
 static void hardware_unsetup(void)
 {
-	kvm_unregister_posted_intr_wakeup_handler(pi_wakeup_handler);
+	if (enable_apicv)
+		kvm_unregister_posted_intr_wakeup_handler(pi_wakeup_handler);
 
 	if (nested)
 		nested_vmx_hardware_unsetup();
@@ -7907,7 +7908,8 @@ static __init int hardware_setup(void)
 	if (r)
 		nested_vmx_hardware_unsetup();
 
-	kvm_register_posted_intr_wakeup_handler(pi_wakeup_handler);
+	if (enable_apicv)
+		kvm_register_posted_intr_wakeup_handler(pi_wakeup_handler);
 
 	return r;
 }
-- 
2.33.0.882.g93a45727a2-goog