linux-kernel - [PATCH MANUALSEL 5.14 2/5] KVM: x86: WARN if APIC HW/SW disable static keys are non-zero on unload

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Message-Id: <20211025203828.1404503-2-sashal@kernel.org>
Date:   Mon, 25 Oct 2021 16:38:24 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, kvm@...r.kernel.org
Subject: [PATCH MANUALSEL 5.14 2/5] KVM: x86: WARN if APIC HW/SW disable static keys are non-zero on unload

From: Sean Christopherson <seanjc@...gle.com>

[ Upstream commit 9139a7a64581c80d157027ae20e86f2f24d4292c ]

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 key is improperly incremented.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Message-Id: <20211013003554.47705-3-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 ba5a27879f1d..18cb699b0a14 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2942,5 +2942,7 @@ 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