[PATCH 5.4 139/215] vfio/pci: Disable auto-enable of exclusive INTx IRQ

Greg Kroah-Hartman
2024-04-11T10:20:53Z

From: Alex Williamson <alex.williamson@redhat.com>

[ Upstream commit fe9a7082684eb059b925c535682e68c34d487d43 ]

Currently for devices requiring masking at the irqchip for INTx, ie.
devices without DisINTx support, the IRQ is enabled in request_irq()
and subsequently disabled as necessary to align with the masked status
flag. This presents a window where the interrupt could fire between
these events, resulting in the IRQ incrementing the disable depth twice.
This would be unrecoverable for a user since the masked flag prevents
nested enables through vfio.

Instead, invert the logic using IRQF_NO_AUTOEN such that exclusive INTx
is never auto-enabled, then unmask as required.

Cc: <stable@vger.kernel.org>
Fixes: 89e1f7d4c66d ("vfio: Add PCI device driver")
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Link: https://lore.kernel.org/r/20240308230557.805580-2-alex.williamson@redhat.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/vfio/pci/vfio_pci_intrs.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)

--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -199,8 +199,15 @@ static int vfio_intx_set_signal(struct v

vdev->ctx[0].trigger = trigger;

+ /*
+ * Devices without DisINTx support require an exclusive interrupt,
+ * IRQ masking is performed at the IRQ chip. The masked status is
+ * protected by vdev->irqlock. Setup the IRQ without auto-enable and
+ * unmask as necessary below under lock. DisINTx is unmodified by
+ * the IRQ configuration and may therefore use auto-enable.
+ */
if (!vdev->pci_2_3)
- irqflags = 0;
+ irqflags = IRQF_NO_AUTOEN;

ret = request_irq(pdev->irq, vfio_intx_handler,
irqflags, vdev->ctx[0].name, vdev);
@@ -211,13 +218,9 @@ static int vfio_intx_set_signal(struct v
return ret;
}

- /*
- * INTx disable will stick across the new irq setup,
- * disable_irq won't.
- */
spin_lock_irqsave(&vdev->irqlock, flags);
- if (!vdev->pci_2_3 && vdev->ctx[0].masked)
- disable_irq_nosync(pdev->irq);
+ if (!vdev->pci_2_3 && !vdev->ctx[0].masked)
+ enable_irq(pdev->irq);
spin_unlock_irqrestore(&vdev->irqlock, flags);

return 0;