[PATCH] vfio: Fix PCI 2.3 shared interrupt

[Alex Williamson <alex.williamson@redhat.com>]

Trying to be too clever with setting the irq_disabled flag.  PCI 2.3
disabled devices can still share IRQs, which can lead to clearing
the irq_disabled flag, preventing the EOI from registering, and leaving
the device without interrupts.  Interrupt handler should only ever
set irq_disabled and we can exit earlier to avoid the config space
access if we know we're disabled.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

 drivers/vfio/vfio_intrs.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/drivers/vfio/vfio_intrs.c b/drivers/vfio/vfio_intrs.c
index 604082c..73e3deb 100644
--- a/drivers/vfio/vfio_intrs.c
+++ b/drivers/vfio/vfio_intrs.c
@@ -57,6 +57,12 @@ irqreturn_t vfio_interrupt(int irq, void *dev_id)
 
 	spin_lock_irq(&vdev->irqlock);
 
+	/* INTX disabled interrupts can still be shared */
+	if (vdev->irq_disabled) {
+		spin_unlock_irq(&vdev->irqlock);
+		return ret;
+	}
+
 	if (vdev->pci_2_3) {
 		pci_block_user_cfg_access(pdev);
 
@@ -87,7 +93,8 @@ done:
 		ret = IRQ_HANDLED;
 	}
 
-	vdev->irq_disabled = (ret == IRQ_HANDLED);
+	if (ret == IRQ_HANDLED)
+		vdev->irq_disabled = true;
 
 	spin_unlock_irq(&vdev->irqlock);