linux-kernel - [PATCH 2/2] KVM: x86: WARN if APIC HW/SW disable static keys are non-zero on unload

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Date:   Tue, 12 Oct 2021 17:35:54 -0700
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,
        syzbot+9fc046ab2b0cf295a063@...kaller.appspotmail.com,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: [PATCH 2/2] KVM: x86: WARN if APIC HW/SW disable static keys are
 non-zero on unload

WARN if the static keys used to track if any vCPU has disabled its APIC
are left elevated at module exit.  Unlike the underflow case, nothing in
the static key infrastructure will complain if a key is left elevated,
and because an elevated key only affects performance, nothing in KVM will
fail if either ey is improperly incremented.

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

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 7af25304bda9..d6ac32f3f650 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2946,5 +2946,7 @@ int kvm_apic_accept_events(struct kvm_vcpu *vcpu)
 void kvm_lapic_exit(void)
 {
 	static_key_deferred_flush(&apic_hw_disabled);
+	WARN_ON(static_branch_unlikely(&apic_hw_disabled.key));
 	static_key_deferred_flush(&apic_sw_disabled);
+	WARN_ON(static_branch_unlikely(&apic_sw_disabled.key));
 }
-- 
2.33.0.1079.g6e70778dc9-goog