linux-kernel - [PATCH v3 3/4] KVM: x86: Check for pending interrupts when APICv is getting disabled

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Message-Id: <20210609150911.1471882-4-vkuznets@redhat.com>
Date:   Wed,  9 Jun 2021 17:09:10 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 3/4] KVM: x86: Check for pending interrupts when APICv is getting disabled

When APICv is active, interrupt injection doesn't raise KVM_REQ_EVENT
request (see __apic_accept_irq()) as the required work is done by hardware.
In case KVM_REQ_APICV_UPDATE collides with such injection, the interrupt
may never get delivered.

Currently, the described situation is hardly possible: all
kvm_request_apicv_update() calls normally happen upon VM creation when
no interrupts are pending. We are, however, going to move unconditional
kvm_request_apicv_update() call from kvm_hv_activate_synic() to
synic_update_vector() and without this fix 'hyperv_connections' test from
kvm-unit-tests gets stuck on IPI delivery attempt right after configuring
a SynIC route which triggers APICv disablement.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/x86.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0f461f111a0b..605dda19642b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8979,6 +8979,15 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
 	vcpu->arch.apicv_active = kvm_apicv_activated(vcpu->kvm);
 	kvm_apic_update_apicv(vcpu);
 	static_call(kvm_x86_refresh_apicv_exec_ctrl)(vcpu);
+
+	/*
+	 * When APICv gets disabled, we may still have injected interrupts
+	 * pending. At the same time, KVM_REQ_EVENT may not be set as APICv was
+	 * still active when the interrupt got accepted. Make sure
+	 * inject_pending_event() is called to check for that.
+	 */
+	if (!vcpu->arch.apicv_active)
+		kvm_make_request(KVM_REQ_EVENT, vcpu);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_update_apicv);

-- 
2.31.1