vfio-pci: Don't use device_lock around AER interrupt setup

device_lock is much too prone to lockups.  For instance if we have a
pending .remove then device_lock is already held.  If userspace
attempts to modify AER signaling after that point, a deadlock occurs.
eventfd setup/teardown is already protected in vfio with the igate
mutex.  AER is not a high performance interrupt, so we can also use
the same mutex to protect signaling versus setup races.

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

2 files changed, 4 insertions, 17 deletions

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 6ab71b9fcf8d..3ffd27f42418 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -883,9 +883,13 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
                 return PCI_ERS_RESULT_DISCONNECT;
         }
 
+        mutex_lock(&vdev->igate);
+
         if (vdev->err_trigger)
                 eventfd_signal(vdev->err_trigger, 1);
 
+        mutex_unlock(&vdev->igate);
+
         vfio_device_put(device);
 
         return PCI_ERS_RESULT_CAN_RECOVER;
diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index 641bc87bdb96..210357691dc0 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -749,54 +749,37 @@ static int vfio_pci_set_err_trigger(struct vfio_pci_device *vdev,
                                     unsigned count, uint32_t flags, void *data)
 {
         int32_t fd = *(int32_t *)data;
-        struct pci_dev *pdev = vdev->pdev;
 
         if ((index != VFIO_PCI_ERR_IRQ_INDEX) ||
             !(flags & VFIO_IRQ_SET_DATA_TYPE_MASK))
                 return -EINVAL;
 
-        /*
-         * device_lock synchronizes setting and checking of
-         * err_trigger. The vfio_pci_aer_err_detected() is also
-         * called with device_lock held.
-         */
-
         /* DATA_NONE/DATA_BOOL enables loopback testing */
-
         if (flags & VFIO_IRQ_SET_DATA_NONE) {
-                device_lock(&pdev->dev);
                 if (vdev->err_trigger)
                         eventfd_signal(vdev->err_trigger, 1);
-                device_unlock(&pdev->dev);
                 return 0;
         } else if (flags & VFIO_IRQ_SET_DATA_BOOL) {
                 uint8_t trigger = *(uint8_t *)data;
-                device_lock(&pdev->dev);
                 if (trigger && vdev->err_trigger)
                         eventfd_signal(vdev->err_trigger, 1);
-                device_unlock(&pdev->dev);
                 return 0;
         }
 
         /* Handle SET_DATA_EVENTFD */
-
         if (fd == -1) {
-                device_lock(&pdev->dev);
                 if (vdev->err_trigger)
                         eventfd_ctx_put(vdev->err_trigger);
                 vdev->err_trigger = NULL;
-                device_unlock(&pdev->dev);
                 return 0;
         } else if (fd >= 0) {
                 struct eventfd_ctx *efdctx;
                 efdctx = eventfd_ctx_fdget(fd);
                 if (IS_ERR(efdctx))
                         return PTR_ERR(efdctx);
-                device_lock(&pdev->dev);
                 if (vdev->err_trigger)
                         eventfd_ctx_put(vdev->err_trigger);
                 vdev->err_trigger = efdctx;
-                device_unlock(&pdev->dev);
                 return 0;
         } else
                 return -EINVAL;