[PATCH v3 3/3] KVM: x86: ioapic: Preserve irr_delivered for duplicate edge interrupts

From: Hao Zhang <[email protected]>

For edge-triggered interrupts, ioapic_set_irq() clears irr_delivered
before checking whether the new edge is a duplicate.  A duplicate edge
is then coalesced without being serviced, leaving the interrupt visible
in KVM_GET_IRQCHIP state even though the original interrupt was already
delivered.

Move the state update after the duplicate-edge check so duplicate edges
do not make a delivered interrupt appear pending during VM migration.

Add a selftest to verify that a duplicate edge interrupt does not make
an already-delivered interrupt visible in the saved IRR state.

Fixes: 5bda6eed2e36 ("KVM: ioapic: Record edge-triggered interrupts delivery status")
Signed-off-by: Hao Zhang <[email protected]>
---
 arch/x86/kvm/ioapic.c                              |  2 +-
 .../testing/selftests/kvm/x86/ioapic_state_test.c  | 47 ++++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
index 24a7cc3b8b7e..676effd674f9 100644
--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -230,11 +230,11 @@ static int ioapic_set_irq(struct kvm_ioapic *ioapic, unsigned int irq,
 	old_irr = ioapic->irr;
 	ioapic->irr |= mask;
 	if (edge) {
-		ioapic->irr_delivered &= ~mask;
 		if (old_irr == ioapic->irr) {
 			ret = 0;
 			goto out;
 		}
+		ioapic->irr_delivered &= ~mask;
 	}
 
 	ret = ioapic_service(ioapic, irq, line_status);
diff --git a/tools/testing/selftests/kvm/x86/ioapic_state_test.c b/tools/testing/selftests/kvm/x86/ioapic_state_test.c
index be5237f34ad2..da0276a1542f 100644
--- a/tools/testing/selftests/kvm/x86/ioapic_state_test.c
+++ b/tools/testing/selftests/kvm/x86/ioapic_state_test.c
@@ -3,7 +3,9 @@
  * Regression tests for in-kernel I/O APIC state.
  */
 
+#include "apic.h"
 #include "kvm_util.h"
+#include "processor.h"
 #include "test_util.h"
 
 #define TEST_IOAPIC_PIN		16
@@ -62,6 +64,16 @@ static int kvm_irq_line_status(struct kvm_vm *vm, int level)
 	return irq.status;
 }
 
+static void assert_ioapic_pin_irr(struct kvm_vm *vm, bool expected)
+{
+	struct kvm_irqchip irqchip;
+
+	get_ioapic(vm, &irqchip);
+	TEST_ASSERT(!!(irqchip.chip.ioapic.irr & (1 << TEST_IOAPIC_PIN)) == expected,
+		    "Expected IOAPIC IRR for pin %u to be %u, got 0x%x",
+		    TEST_IOAPIC_PIN, expected, irqchip.chip.ioapic.irr);
+}
+
 static void test_no_remote_irr_for_undelivered_level_interrupt(void)
 {
 	struct kvm_irqchip irqchip;
@@ -84,9 +96,44 @@ static void test_no_remote_irr_for_undelivered_level_interrupt(void)
 	kvm_vm_free(vm);
 }
 
+static void test_duplicate_edge_interrupt_preserves_delivery_state(void)
+{
+	struct kvm_lapic_state lapic;
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	u64 apicbase;
+	int status;
+
+	vm = vm_create_with_one_vcpu(&vcpu, NULL);
+	apicbase = vcpu_get_msr(vcpu, MSR_IA32_APICBASE);
+	vcpu_set_msr(vcpu, MSR_IA32_APICBASE,
+		     apicbase | MSR_IA32_APICBASE_ENABLE);
+	vcpu_ioctl(vcpu, KVM_GET_LAPIC, &lapic);
+	*(u32 *)(lapic.regs + APIC_SPIV) |= APIC_SPIV_APIC_ENABLED;
+	vcpu_ioctl(vcpu, KVM_SET_LAPIC, &lapic);
+
+	set_ioapic_entry(vm, false, vcpu->id);
+
+	status = kvm_irq_line_status(vm, 1);
+	TEST_ASSERT(status > 0,
+		    "Expected edge interrupt delivery, got %d", status);
+
+	assert_ioapic_pin_irr(vm, false);
+
+	status = kvm_irq_line_status(vm, 1);
+	TEST_ASSERT(!status,
+		    "Expected duplicate edge interrupt to be coalesced, got %d",
+		    status);
+
+	assert_ioapic_pin_irr(vm, false);
+
+	kvm_vm_free(vm);
+}
+
 int main(void)
 {
 	test_no_remote_irr_for_undelivered_level_interrupt();
+	test_duplicate_edge_interrupt_preserves_delivery_state();
 
 	return 0;
 }
-- 
2.15.0