vfio-pci: Attempt bus/slot reset on release

Each time a device is released, mark whether a local reset was
successful or whether a bus/slot reset is needed.  If a reset is
needed and all of the affected devices are bound to vfio-pci and
unused, allow the reset.  This is most useful when the userspace
driver is killed and releases all the devices in an unclean state,
such as when a QEMU VM quits.

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

2 files changed, 113 insertions, 0 deletions

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index c9d756b7ee9e..1651c0769b72 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -39,6 +39,8 @@ MODULE_PARM_DESC(nointxmask,
 
 static DEFINE_MUTEX(driver_lock);
 
+static void vfio_pci_try_bus_reset(struct vfio_pci_device *vdev);
+
 static int vfio_pci_enable(struct vfio_pci_device *vdev)
 {
         struct pci_dev *pdev = vdev->pdev;
@@ -123,6 +125,8 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
                 vdev->barmap[bar] = NULL;
         }
 
+        vdev->needs_reset = true;
+
         /*
          * If we have saved state, restore it.  If we can reset the device,
          * even better.  Resetting with current state seems better than
@@ -154,11 +158,15 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
                 if (ret)
                         pr_warn("%s: Failed to reset device %s (%d)\n",
                                 __func__, dev_name(&pdev->dev), ret);
+                else
+                        vdev->needs_reset = false;
         }
 
         pci_restore_state(pdev);
 out:
         pci_disable_device(pdev);
+
+        vfio_pci_try_bus_reset(vdev);
 }
 
 static void vfio_pci_release(void *device_data)
@@ -923,6 +931,110 @@ static struct pci_driver vfio_pci_driver = {
         .err_handler    = &vfio_err_handlers,
 };
 
+/*
+ * Test whether a reset is necessary and possible.  We mark devices as
+ * needs_reset when they are released, but don't have a function-local reset
+ * available.  If any of these exist in the affected devices, we want to do
+ * a bus/slot reset.  We also need all of the affected devices to be unused,
+ * so we abort if any device has a non-zero refcnt.  driver_lock prevents a
+ * device from being opened during the scan or unbound from vfio-pci.
+ */
+static int vfio_pci_test_bus_reset(struct pci_dev *pdev, void *data)
+{
+        bool *needs_reset = data;
+        struct pci_driver *pci_drv = ACCESS_ONCE(pdev->driver);
+        int ret = -EBUSY;
+
+        if (pci_drv == &vfio_pci_driver) {
+                struct vfio_device *device;
+                struct vfio_pci_device *vdev;
+
+                device = vfio_device_get_from_dev(&pdev->dev);
+                if (!device)
+                        return ret;
+
+                vdev = vfio_device_data(device);
+                if (vdev) {
+                        if (vdev->needs_reset)
+                                *needs_reset = true;
+
+                        if (!vdev->refcnt)
+                                ret = 0;
+                }
+
+                vfio_device_put(device);
+        }
+
+        /*
+         * TODO: vfio-core considers groups to be viable even if some devices
+         * are attached to known drivers, like pci-stub or pcieport.  We can't
+         * freeze devices from being unbound to those drivers like we can
+         * here though, so it would be racy to test for them.  We also can't
+         * use device_lock() to prevent changes as that would interfere with
+         * PCI-core taking device_lock during bus reset.  For now, we require
+         * devices to be bound to vfio-pci to get a bus/slot reset on release.
+         */
+
+        return ret;
+}
+
+/* Clear needs_reset on all affected devices after successful bus/slot reset */
+static int vfio_pci_clear_needs_reset(struct pci_dev *pdev, void *data)
+{
+        struct pci_driver *pci_drv = ACCESS_ONCE(pdev->driver);
+
+        if (pci_drv == &vfio_pci_driver) {
+                struct vfio_device *device;
+                struct vfio_pci_device *vdev;
+
+                device = vfio_device_get_from_dev(&pdev->dev);
+                if (!device)
+                        return 0;
+
+                vdev = vfio_device_data(device);
+                if (vdev)
+                        vdev->needs_reset = false;
+
+                vfio_device_put(device);
+        }
+
+        return 0;
+}
+
+/*
+ * Attempt to do a bus/slot reset if there are devices affected by a reset for
+ * this device that are needs_reset and all of the affected devices are unused
+ * (!refcnt).  Callers of this function are required to hold driver_lock such
+ * that devices can not be unbound from vfio-pci or opened by a user while we
+ * test for and perform a bus/slot reset.
+ */
+static void vfio_pci_try_bus_reset(struct vfio_pci_device *vdev)
+{
+        bool needs_reset = false, slot = false;
+        int ret;
+
+        if (!pci_probe_reset_slot(vdev->pdev->slot))
+                slot = true;
+        else if (pci_probe_reset_bus(vdev->pdev->bus))
+                return;
+
+        if (vfio_pci_for_each_slot_or_bus(vdev->pdev,
+                                          vfio_pci_test_bus_reset,
+                                          &needs_reset, slot) || !needs_reset)
+                return;
+
+        if (slot)
+                ret = pci_try_reset_slot(vdev->pdev->slot);
+        else
+                ret = pci_try_reset_bus(vdev->pdev->bus);
+
+        if (ret)
+                return;
+
+        vfio_pci_for_each_slot_or_bus(vdev->pdev,
+                                      vfio_pci_clear_needs_reset, NULL, slot);
+}
+
 static void __exit vfio_pci_cleanup(void)
 {
         pci_unregister_driver(&vfio_pci_driver);
diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
index 31e7a30196ab..671c17a6e6d0 100644
--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h
@@ -54,6 +54,7 @@ struct vfio_pci_device {
         bool                    extended_caps;
         bool                    bardirty;
         bool                    has_vga;
+        bool                    needs_reset;
         struct pci_saved_state  *pci_saved_state;
         int                     refcnt;
         struct eventfd_ctx      *err_trigger;