[PATCH v5 1/6] KVM: x86: ioapic: Update remote_irr only after successful delivery

[Hao Zhang <hao_zhang_kdev@163.com>]

From: Hao Zhang <zhanghao1@kylinos.cn>

The I/O APIC sets remote_irr for level-triggered interrupts that have
been accepted by a local APIC and are waiting for an EOI.

ioapic_service() currently treats any non-zero return from
kvm_irq_delivery_to_apic() as successful delivery.  But negative return
values are failures, not successful delivery.  Setting remote_irr after
such a failed delivery leaves the pin blocked forever waiting for an EOI
that will never be generated.

The bug dates back to commit 4925663a079c ("KVM: Report IRQ injection
status to userspace."), which made ioapic_service() preserve and return
the delivery result, initialized the result to -1, but kept using
"ret != 0" as the condition for setting remote_irr.  As a result, any
negative delivery failure that reaches this path is incorrectly treated
as a delivered level-triggered interrupt.

Update remote_irr only when the delivery result is positive, i.e. when
at least one local APIC accepted the interrupt.

Fixes: 4925663a079c ("KVM: Report IRQ injection status to userspace.")
Reviewed-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Hao Zhang <zhanghao1@kylinos.cn>
---
 arch/x86/kvm/ioapic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
index 757667fb2bfa..24a7cc3b8b7e 100644
--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -491,7 +491,7 @@ static int ioapic_service(struct kvm_ioapic *ioapic, int irq, bool line_status)
 	} else
 		ret = kvm_irq_delivery_to_apic(ioapic->kvm, NULL, &irqe);
 
-	if (ret && irqe.trig_mode == IOAPIC_LEVEL_TRIG)
+	if (ret > 0 && irqe.trig_mode == IOAPIC_LEVEL_TRIG)
 		entry->fields.remote_irr = 1;
 
 	return ret;
-- 
2.15.0