linux-kernel - [PATCH 4/4] KVM: x86: Skip KVM_GUESTDBG_BLOCKIRQ APICv update if APICv is disabled

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Message-Id: <20220416034249.2609491-5-seanjc@google.com>
Date:   Sat, 16 Apr 2022 03:42:49 +0000
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, Gaoning Pan <pgn@....edu.cn>,
        Yongkang Jia <kangel@....edu.cn>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 4/4] KVM: x86: Skip KVM_GUESTDBG_BLOCKIRQ APICv update if
 APICv is disabled

Skip the APICv inhibit update for KVM_GUESTDBG_BLOCKIRQ if APICv is
disabled at the module level to avoid having to acquire the mutex and
potentially process all vCPUs. The DISABLE inhibit will (barring bugs)
never be lifted, so piling on more inhibits is unnecessary.

Fixes: cae72dcc3b21 ("KVM: x86: inhibit APICv when KVM_GUESTDBG_BLOCKIRQ active")
Cc: Maxim Levitsky <mlevitsk@...hat.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 09a270cc1c8f..16c5fa7d165d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11048,6 +11048,9 @@ static void kvm_arch_vcpu_guestdbg_update_apicv_inhibit(struct kvm *kvm)
 	struct kvm_vcpu *vcpu;
 	unsigned long i;
 
+	if (!enable_apicv)
+		return;
+
 	down_write(&kvm->arch.apicv_update_lock);
 
 	kvm_for_each_vcpu(i, vcpu, kvm) {
-- 
2.36.0.rc0.470.gd361397f0d-goog