linux-kernel - [PATCH v2] KVM: x86: ioapic: Fix level-triggered EOI and userspace I/OAPIC reconfigure race

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Message-ID: <20221208094415.12723-1-attofari@amazon.de>
Date:   Thu, 8 Dec 2022 09:44:14 +0000
From:   Adamos Ttofari <attofari@...zon.de>
To:     unlisted-recipients:; (no To-header on input)
CC:     <attofari@...zon.de>, <dwmw@...zon.co.uk>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Nikita Leshenko <nikita.leshchenko@...cle.com>,
        Liran Alon <liran.alon@...cle.com>,
        "Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] KVM: x86: ioapic: Fix level-triggered EOI and userspace I/OAPIC reconfigure race

When scanning userspace I/OAPIC entries, intercept EOI for level-triggered
IRQs if the current vCPU has a pending and/or in-service IRQ for the
vector in its local API, even if the vCPU doesn't match the new entry's
destination.  This fixes a race between userspace I/OAPIC reconfiguration
and IRQ delivery that results in the vector's bit being left set in the
remote IRR due to the eventual EOI not being forwarded to the userspace
I/OAPIC.

Commit 0fc5a36dd6b3 ("KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC
reconfigure race") fixed the in-kernel IOAPIC, but not the userspace
IOAPIC configuration, which has a similar race.

Fixes: 0fc5a36dd6b3 ("KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC reconfigure race")

Signed-off-by: Adamos Ttofari <attofari@...zon.de>
---
 arch/x86/kvm/irq_comm.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index 0687162c4f22..3742d9adacfc 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -426,8 +426,9 @@ void kvm_scan_ioapic_routes(struct kvm_vcpu *vcpu,
 			kvm_set_msi_irq(vcpu->kvm, entry, &irq);

 			if (irq.trig_mode &&
-			    kvm_apic_match_dest(vcpu, NULL, APIC_DEST_NOSHORT,
-						irq.dest_id, irq.dest_mode))
+			    (kvm_apic_match_dest(vcpu, NULL, APIC_DEST_NOSHORT,
+						 irq.dest_id, irq.dest_mode) ||
+			     kvm_apic_pending_eoi(vcpu, irq.vector)))
 				__set_bit(irq.vector, ioapic_handled_vectors);
 		}
 	}
-- 
2.38.1

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