vfio/pci: Disable auto-enable of exclusive INTx IRQ

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>

diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index 237beac8380975110231503e0d30f331ba64e2d5..136101179fcbdc97cc578e142d81374358874607 100644 (file)
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -296,8 +296,15 @@ static int vfio_intx_set_signal(struct vfio_pci_core_device *vdev, int fd)
 
        ctx->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, ctx->name, vdev);
@@ -308,13 +315,9 @@ static int vfio_intx_set_signal(struct vfio_pci_core_device *vdev, int fd)
                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 && ctx->masked)
-               disable_irq_nosync(pdev->irq);
+       if (!vdev->pci_2_3 && !ctx->masked)
+               enable_irq(pdev->irq);
        spin_unlock_irqrestore(&vdev->irqlock, flags);
 
        return 0;