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Message-ID: <20140930001533.17278.33091.stgit@gimli.home>
Date: Mon, 29 Sep 2014 18:15:51 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: alex.williamson@...hat.com, kvm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] vfio-pci: Fix remove path locking
Locking both the remove() and release() path results in a deadlock
that should have been obvious. To fix this we can get and hold the
vfio_device reference as we evaluate whether to do a bus/slot reset.
This will automatically block any remove() calls, allowing us to
remove the explict lock. Fixes 61d792562b53.
Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
Cc: stable@...r.kernel.org [3.17]
---
drivers/vfio/pci/vfio_pci.c | 136 ++++++++++++++++++-------------------------
1 file changed, 57 insertions(+), 79 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index f782533..9558da3 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -876,15 +876,11 @@ static void vfio_pci_remove(struct pci_dev *pdev)
{
struct vfio_pci_device *vdev;
- mutex_lock(&driver_lock);
-
vdev = vfio_del_group_dev(&pdev->dev);
if (vdev) {
iommu_group_put(pdev->dev.iommu_group);
kfree(vdev);
}
-
- mutex_unlock(&driver_lock);
}
static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
@@ -927,108 +923,90 @@ 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;
-}
+struct vfio_devices {
+ struct vfio_device **devices;
+ int cur_index;
+ int max_index;
+};
-/* 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)
+static int vfio_pci_get_devs(struct pci_dev *pdev, void *data)
{
+ struct vfio_devices *devs = 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;
+ if (pci_drv != &vfio_pci_driver)
+ return -EBUSY;
- device = vfio_device_get_from_dev(&pdev->dev);
- if (!device)
- return 0;
+ if (devs->cur_index == devs->max_index)
+ return -ENOSPC;
- vdev = vfio_device_data(device);
- if (vdev)
- vdev->needs_reset = false;
-
- vfio_device_put(device);
- }
+ devs->devices[devs->cur_index] = vfio_device_get_from_dev(&pdev->dev);
+ if (!devs->devices[devs->cur_index])
+ return -EINVAL;
+ devs->cur_index++;
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.
+ * (!refcnt). Callers are required to hold driver_lock when calling this to
+ * prevent device opens and concurrent bus reset attempts. We prevent device
+ * unbinds by acquiring and holding a reference to the vfio_device.
+ *
+ * NB: vfio-core considers a group to be viable even if some devices are
+ * bound to drivers like pci-stub or pcieport. Here we require all devices
+ * to be bound to vfio_pci since that's the only way we can be sure they
+ * stay put.
*/
static void vfio_pci_try_bus_reset(struct vfio_pci_device *vdev)
{
+ struct vfio_devices devs = { .cur_index = 0 };
+ int i = 0, ret = -EINVAL;
bool needs_reset = false, slot = false;
- int ret;
+ struct vfio_pci_device *tmp;
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)
+ if (vfio_pci_for_each_slot_or_bus(vdev->pdev, vfio_pci_count_devs,
+ &i, slot) || !i)
return;
- if (slot)
- ret = pci_try_reset_slot(vdev->pdev->slot);
- else
- ret = pci_try_reset_bus(vdev->pdev->bus);
-
- if (ret)
+ devs.max_index = i;
+ devs.devices = kcalloc(i, sizeof(struct vfio_device *), GFP_KERNEL);
+ if (!devs.devices)
return;
- vfio_pci_for_each_slot_or_bus(vdev->pdev,
- vfio_pci_clear_needs_reset, NULL, slot);
+ if (vfio_pci_for_each_slot_or_bus(vdev->pdev,
+ vfio_pci_get_devs, &devs, slot))
+ goto put_devs;
+
+ for (i = 0; i < devs.cur_index; i++) {
+ tmp = vfio_device_data(devs.devices[i]);
+ if (tmp->needs_reset)
+ needs_reset = true;
+ if (tmp->refcnt)
+ goto put_devs;
+ }
+
+ if (needs_reset)
+ ret = slot ? pci_try_reset_slot(vdev->pdev->slot) :
+ pci_try_reset_bus(vdev->pdev->bus);
+
+put_devs:
+ for (i = 0; i < devs.cur_index; i++) {
+ if (!ret) {
+ tmp = vfio_device_data(devs.devices[i]);
+ tmp->needs_reset = false;
+ }
+ vfio_device_put(devs.devices[i]);
+ }
+
+ kfree(devs.devices);
}
static void __exit vfio_pci_cleanup(void)
--
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